Review Article WRKY Proteins: Signaling and Regulation of ...Review Article WRKY Proteins: Signaling and Regulation of Expression during Abiotic Stress Responses AdityaBanerjeeandAryadeepRoychoudhury

Review ArticleWRKY Proteins Signaling and Regulation ofExpression during Abiotic Stress Responses

Aditya Banerjee and Aryadeep Roychoudhury

Postgraduate Department of Biotechnology St Xavierrsquos College (Autonomous) 30 Mother Teresa SaraniKolkata West Bengal 700016 India

Correspondence should be addressed to Aryadeep Roychoudhury aryadeeprcgmailcom

Received 28 December 2014 Revised 3 March 2015 Accepted 7 March 2015

Academic Editor Shyi Dong Yeh

Copyright copy 2015 A Banerjee and A Roychoudhury This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

WRKY proteins are emerging players in plant signaling and have been thoroughly reported to play important roles in plants underbiotic stress like pathogen attack However recent advances in this field do reveal the enormous significance of these proteins ineliciting responses induced by abiotic stresses WRKY proteins act as major transcription factors either as positive or negativeregulators Specific WRKY factors which help in the expression of a cluster of stress-responsive genes are being targeted andgenetically modified to induce improved abiotic stress tolerance in plants The knowledge regarding the signaling cascade leadingto the activation of the WRKY proteins their interaction with other proteins of the signaling pathway and the downstream genesactivated by them are altogether vital for justified targeting of the WRKY genes WRKY proteins have also been considered togenerate tolerance against multiple abiotic stresses with possible roles in mediating a cross talk between abiotic and biotic stressresponses In this review we have reckoned the diverse signaling pattern and biological functions of WRKY proteins throughoutthe plant kingdom along with the growing prospects in this field of research

1 Introduction

All sustaining living organisms especially the sessile ones likeplants are always exposed to a variety of conditions whichmay cause deleterious impacts on all phenological stages ofdevelopment Such adverse conditions are called stress forthat particular organism Harsh environmental conditionswhich hinder the proper physiological growth of the plantsystem are called abiotic stresses which include drought soilsalinity heavy metal low temperature radiation and otherforms of oxidative stresses Adaptation to such environmentalstress is essential not only for development of the individualplant but also for the stability of its successive generationsGenetic manipulation of crop plants has been undertaken todevelop stress-resistant crop varieties The notion of bring-ing up such genetically modified (GM) crops has becomestronger after it was estimated that the maximum worldwidecrop yield loss (70) can be attributed to abiotic stresssensitivity of the crops

Natural evolution in plants has also enhanced multiplelevel molecular mechanisms to tackle abiotic stress by theinduction of stress-responsive and stress-tolerance genes [1]Such induction is highly dependent on proper perceptionand transduction of the environmental cues via a signalingcascade [2] Transcriptional regulation of the stress-inducedgenes plays a pivotal role in developing stress tolerance inplants Such regulation is mainly dependent on the temporaland spatial functioning of the transcription factors (TFs)[3] Presence of 2100 and 2300 TFs has been reported inArabidopsis thaliana and Oryza sativa respectively Thisshows the enormous importance of TFs in regulating geneexpression otherwise such a large portion of the genomewould not have been devoted for coding the TFs alone [4]Upregulation of specific TFs corresponding to that of somestress-induced genes has unleashed a complex network ofinterconnected cross talks Researchers are trying to findwhether specific stress-responsive TFs apart from upregu-lating their target genes also essentially regulate a complete

Hindawi Publishing Corporatione Scientific World JournalVolume 2015 Article ID 807560 17 pageshttpdxdoiorg1011552015807560

2 The Scientific World Journal

package of stress-induced responses like posttranslationaland epigenetic modifications namely variable nucleosomedistribution histone modification DNA methylation andsynthesis of nonprotein-coding RNAs (npcRNAs) [5]

2 TFs in Abiotic Stress

TFs have been a major target in improving stress tolerancein plants due to their ability to control critical downstreamresponses by regulating target gene transcription Entire cas-cades of signal transduction get activated when TFs interactwith specific cis-acting response elements in the promotersof stress-inducible genes This enhances combinatorial tol-erance against multiple stresses [6] Thus these TFs them-selves can be genetically upregulated to increase the stress-induced gene responsiveness and hence the overall stresstolerance The principal TFs involved in stress managementlie in the AP2ERF (Apetala2ethylene response factor) bZIP(basic leucine zipper) NAC (No Apical Meristem ATAF12Cup-Shaped Cotyledon 2) MYB C2H2 Zn finger SBP(Squamosa-Promoter Binding Protein) and WRKY (TFscontaining highly conserved WRKY domain) superfamilies[7] The bZIP TF family consists of a large number of TFswith diverse roles and ability to bind to abscisic acid- (ABA-)responsive elements (ABREs) [8] The MYB family of TFsare regulators of several responses pertaining to secondarymetabolism cell cycle biotic defence and abiotic stress [9]The NAC TFs like stress responsive NAC (SNAC) genes whenoverexpressed improve the drought tolerance in rice [10] Inthis review we will focus on the intricate relation of one ofthe largest families that is the WRKY superfamily of TFs inenhancing stress tolerance in various plant species

3 WRKY Proteins StructuralCharacterization and Classification

TheWRKY TFs were first identified in sweet potato (SPF1) asDNA-binding proteins [11] Evolution ofMutator orMutator-like transposable elements (MULEs) gave rise to the WRKY-GCM1 superfamily of Zn finger TFs [12] The TFs containingtheDNAbinding domainGCM have been clumped togetherwith the WRKY TFs to be classified as the WRKY-GCM1superfamily [13] WRKY genes are quite common in plantsthough some nonplant species have also been identifiedwhich carry such genes in their genomes 74 WRKY genesin Arabidopsis more than 100 genes in rice 197 genes insoybean 66 genes in papaya 104 genes in poplar 68 genesin sorghum 38 genes in Physcomitrella patens 35 genes inSelaginella moellendorffii 80 genes in Pinus more than 45genes in barley 56 genes in Ricinus communis 119 genes inthe B73 inbred line of maize 55 genes in Cucumis sativus120 genes in Gossypium raimondii and 59 candidate genes inVitis vinifera have been identified [14ndash19] The large numberof genes present in the genomes of several plant species doeshint about a pivotal role played by these TFs in downstreamgene activation The WRKY domain has a conserved N-terminal sequence ofWRKYGQK along with a Zn finger-likemotif which can be either Cx

4-5Cx22-23HxH (C2H2 type) or

Cx7Cx23HxC (C2HC type) The WRKY domain can be 60

amino acids long and binds DNA [20] Slight variations ofWRKYGQK can be found in some WRKY TFs The WRKYDNA-binding domain generally binds to theW-box elementscontaining the TTGAC(CT) motif though the flankingsequence adjoining theW-box dictates the binding selectivityof the TF [20] For example in contrast to other WRKYTFs WRKY6 and WRKY11 of Arabidopsis have high affinitytowards a G base upstream of the core motif of the W-box[21]

Arabidopsis being the model plant has the most wellclassified list ofWRKYproteins (Table 1)These proteins havebeen divided into three distinct groups depending on thenumbers of WRKY domains present and the diversity inthe Zn finger motifs found in them [22] The bifurcation inthe groups occurred mainly due to the number of WRKYdomains The proteins belonging to Group I have twodistinct WRKY domains while the proteins belonging toboth Groups II and III have single domains The differencebetween the proteins of Groups II and III lies in the fact thatthe former group consists of proteins with the same Cys2-His2 Zn finger motif while those belonging to the lattergroup have different Cys2-HisCys Cys2-His2 Zn fingermotif[14] On the basis of the presence of additional conservedstructural motifs Groups II and III have been further dividedinto subgroups Group IV WRKY has been characterized bythe loss of the Zn finger motif Though these proteins werethought to be nonfunctional they were found in higher algae(Bathycoccus prasinos) and some plants like rice and Vitisvinifera Recently the VvWRKYs from V vinifera have beenreported to play crucial roles in generating cold stress toler-ance in grapevines (Table 1) Structures like nuclear localiza-tion signal (NLS) leucine zippers SerThr rich stretches Glnand Pro rich stretches kinase domains and pathogenesis-related TIR-NBS-LRR domains have also been identified inthe WRKY proteins which infers the diverse roles played bythese proteins in multifarious signaling cascades [14]

4 WRKY Proteins in Stress

Under normal cellular conditions theWRKY genes regulateimportant functions related to the developmental processesin plants The expression of the Dactylis glomerata WRKYgene DGE1 is essential for proper somatic embryogen-esis [23] Strong expression of ScWRKY1 is induced inthe fertilized ovules in potato at the late torpedo stage ofembryogenesis [24] Transparent Testa Glabra 2 (TTG2) isalso named as WRKY44 and is involved in the regulation ofdevelopment of trichomes and root hairs [25] Starch produc-tion in endosperm is governed by aWRKYprotein SUSIBA2High expression ofMiniseed3 gene encoding AtWRKY10 hasbeen reported in pollens globular embryos and developingendosperms [25]

The WRKY proteins play prominent roles in the reg-ulation of transcriptional reprogramming associated withplant stress responses (Table 2) Such WRKY-mediated tran-scriptional response can be against both biotic and abioticfactors [14]TheWRKYproteins function via protein-proteininteractions and even cross regulation and autoregulation

The Scientific World Journal 3

Table1Major

families

ofWRK

Yproteins

with

associated

characteris

tics

Genefam

ilyname

Genefam

ilysubclass

Proteinassociated

Proteintype

References

Group

Imdash

AtWRK

Y1A

tWRK

Y2A

tWRK

Y1A

tWRK

Y2A

tWRK

Y3A

tWRK

Y4A

tWRK

Y10

AtWRK

Y19AtWRK

Y20AtWRK

Y25AtWRK

Y26AtWRK

Y32AtWRK

Y33

AtWRK

Y34AtWRK

Y44AtWRK

Y45AtWRK

Y58AtWRK

Y73OsW

RKY2

4OSW

RKY7

0OsW

RKY7

8OsW

RKY3

0OsW

RKY4

OsW

RKY6

3OsW

RKY6

1OsW

RKY8

1

Thep

roteinsc

ontain

two

WRK

Ydo

mains

Group

II(Arabidopsis)

IIaAtWRK

Y18AtWRK

Y40AtWRK

Y60

Sing

leWRK

Ydo

mainwith

thes

ameC

ys2-His2

Znfin

germ

otif

IIb

AtWRK

Y6A

tWRK

Y9A

tWRK

Y31AtWRK

Y36AtWRK

Y42AtWRK

Y47

AtWRK

Y61AtWRK

Y72

IIcAtWRK

Y8A

tWRK

Y12AtWRK

Y13AtWRK

Y23AtWRK

Y24AtWRK

Y28

AtWRK

Y43AtWRK

Y48AtWRK

Y49AtWRK

Y50AtWRK

Y51AtWRK

Y56

AtWRK

Y57AtWRK

Y59AtWRK

Y68AtWRK

Y71AtWRK

Y75

IIdAtWRK

Y7A

tWRK

Y11AtWRK

Y15AtWRK

Y17AtWRK

Y21AtWRK

Y39

AtWRK

Y74

[131420ndash

22117118]

IIeAtWRK

Y14AtWRK

Y16AtWRK

Y22AtWRK

Y27AtWRK

Y29AtWRK

Y35

AtWRK

Y65AtWRK

Y69

IIIa

AtWRK

Y38AtWRK

Y62AtWRK

Y63AtWRK

Y64AtWRK

Y66AtWRK

Y67

Group

II(rice)

mdashOsW

RKY5

1OsW

RKY4

2OsW

RKY2

5OsW

RKY4

4OsW

RKY6

8OsW

RKY6

OsW

RKY3

7OsW

RKY6

6OsW

RKY2

OsW

RKY13

Group

III

(Arabidopsis)

IIIb

AtWRK

Y30AtWRK

Y41AtWRK

Y46AtWRK

Y53AtWRK

Y54AtWRK

Y55

AtWRK

Y70

Sing

leWRK

Ydo

mainwith

different

Cys2-H

isCy

sCy

s2-H

is2Zn

fingerm

otif

Group

III(ric

e)mdash

OsW

RKY2

2OsW

RKY2

0OsW

RKY6

9OsW

RKY7

4OsW

RKY15OsW

RKY19

OsW

RKY4

5OsW

RKY7

5

Group

IVIVa

OsW

RKY3

3OsW

RKY3

8Presence

ofpartialZ

nfin

germ

otif

IVb

VvWRK

Y02Vv

WRK

Y29OsW

RKY5

6OsW

RKY5

8OsW

RKY5

2Lo

ssof

Znfin

germ

otif

ldquoAtrdquorefersto

Arabidopsis

thaliana

ldquoOsrdquoto

Oryza

sativaandldquoV

vrdquoto

Vitis

vinifer

a


Table2Ro

leof

WRK

Yproteins

inbo

thabiotic

andbioticstr

esses

Stresstype

Gene

Indu

ciblefactors

Functio

nin

stress

References

Abiotic

stress

AtWRK

Y2NaC

lmannitol

Negatively

regu

latesA

BAsig

nalin

g[74]

AtWRK

Y18

ABA

ABA

signalin

gandsalttolerance

[119]

AtWRK

Y26

Heat

Heattolerance

[34]

AtWRK

Y39

Heat

Heattolerance

[96]

AtWRK

Y40

ABA

ABA

signalin

g[119]

OsW

RKY0

8Droug

htsalinityA

BAand

oxidative

stress

Tolerancetow

ards

oxidatives

tress

[120]

OsW

RKY11

Heatdrou

ght

Xerothermicstr

esstolerance

[121]

OsW

RKY8

9Salin

ityA

BAand

UV-B

UV-Bradiationtolerance

[122]

OsW

RKY4

5Salt

drou

ght

Saltanddrou

ghttolerance

[123]

OsW

RKY7

2Salt

drou

ght

Saltanddrou

ghttolerance

[124]

GmWRK

Y21

Salt

coldand

drou

ght

Coldtolerance

[72]

GmWRK

Y54

Salt

drou

ght

Saltanddrou

ghttolerance

[72]

Bioticstr

ess

AtWRK

Y38

Targetof

NPR

1duringSyste

micAc

quire

dRe

sistance(SA

R)IncreasesS

alicylicAc

id-(SA

-)mediated

respon

se[125]

AtWRK

Y53

Targetof

NPR

1duringSA

RIncreasesS

A-mediatedrespon

se[125]

AtWRK

Y66

Targetof

NPR

1duringSA

RIncreasesS

A-mediatedrespon

se[125]

AtWRK

Y70

Targetof

NPR

1duringSA

RNod

eofcon

vergence

forS

A-mediated

andjasm

onicacid-(JA-)mediated

defences

ignalin

g[126]

OsW

RKY3

1Magna

porthe

oryzae

Increasedresistance

[127]

OsW

RKY4

5Moryzae

Increasedresistance

[128]

OsW

RKY7

7Pseudomonas

syrin

gae

Positively

regu

latesp

lant

basalresistance

[129]

HvW

RKY10

EffectorT

riggeredIm

mun

ity(ETI)

ETIa

ctivator

[130]


Arabidopsis

thaliana

ldquoOsrdquoto

Oryza

sativaldquoG

mrdquotoGlycinem

axand

ldquoHvrdquo

toHordeum

vulga

re


Detailed study on themechanisms of signaling and transcrip-tional regulations has unveiled the association of the WRKYproteins with mitogen-activated protein kinases (MAPKs)MAPKKs 14-3-3 proteins calmodulin histone deacetylasesdisease-resistance proteins and other WRKY TFs [26]

Though we will focus on the roles of WRKY in abioticstress these proteins have diverse roles in biotic stress aswell Disease resistance and crop yield in the important tropiccrop Theobroma cacao have been developed by identifyingspecific WRKY loci as the genetic markers [27] In thisreview efforts have been made to improve WRKY loci asgenetic markers against both abiotic and biotic stressesUpon designing the complementary PCR primers against theWRKY domains of Group I and Group II (andashc) proteins 16WRKY fragments were isolated from a mixture of T cacaoDNA using one pair of primers [27] Four among these16 fragments contained single nucleotide polymorphismswithin the intron and could be considered as molecularmarkers after further experimentations [27]

Abiotic stresses like drought salinity radiation and coldinduce the activity of several WRKY proteins which functionin synchronization to confer resistance against the particularstress or provide a combinatorial effect on multiple stressresistance Out of the 13 OsWRKY genes 11 show variableresponses towards salt stress polyethylene glycol (PEG) coldor heat stresses [28] In wheat majority (8 out of 15) of theWRKY genes were transcribed in response to cold heatNaCl and PEG treatment [29] Induction of 18 AtWRKYgenes in the roots of Arabidopsis plants treated with 150mMNaCl was confirmed via microarray profiling [30] The rapidexpression of WRKY genes following stress has led to theargument whether such transient increase inWRKY proteinsis independent of the de novo synthesis of the regulatory fac-tors [22] Both activation of adaptive responses and transcrip-tional regulation of stress-induced genes are actually possibledue to the immediate early expression ofWRKY genesThusthe WRKY protein level in the cell increases sharply andthis rise in protein accumulation aids them to regulate targetgene transcription by associating with the cis-acting responseelements [14] Table 2 is a concise representation of the role ofWRKY genes in stress However the table does emphasise onthe fact that WRKY TFs mediate tolerance to several abioticstresses via transcriptional reprogramming and control ofsignaling cascades Expression patterns of WRKY TFs thushave been intricately studied in order to find a proper basisand clue towards overexpressing particular WRKY proteinsof choice through transgenic approach

5 WRKY-Dependent SignalingPathways in Abiotic Stress

51 Autoregulation and Cross Regulation The notion ofWRKYproteins involved in critical stress responses obviouslymakes extensive regulation of the signaling pathway manda-tory In response to both external and internal stimuliWRKYproteins bind toW-box-containing promoters and trigger theexpression of target stress-responsive genes This triggeringis often autoregulated by the WRKY protein itself or by

separate WRKY TFs (cross regulation) [26] Three GroupIIa WRKY proteins in Arabidopsis AtWRKY18 AtWRKY40and AtWRKY60 have leucine zipper motifs at their N-termini via which they interact among themselves [31] ThePcWRKY1 of parsley (Petroselinum crispum) apart frombinding to its target W-box also has affinity towards bindingthe promoters of PcWRKY3 and even that of the marker genePcPR1 [32]TheMAPK36 activatesWRKY33 expressionTheWRKY33 proteins in vivo autoregulate their expressions via apositive feedback loop by binding to their own promoter [33]Cross regulation among WRKY25 WRKY26 and WRKY33is essential in promoting tolerance against high temperaturestress [34] The AtWRKY18 AtWRKY40 and AtWRKY60are directly bound to their respective promoters in order tonegatively regulate their expression patterns [13] The aboveinstances obviously prove the importance of autoregulationand cross regulation in maintaining the homeostasis ofWRKY protein expression in the cell

52 Regulation of WRKY Expression byMAPKs TheMAPKsplay important roles in transduction of downstream sig-nals in ABA-dependent stress response Wound-inducedprotein kinase (WIPK) and salicylic acid- (SA-) inducedprotein kinase (SIPK) play important roles in biotic stresseslike pathogen invasions [35] The AtMPK3 AtMPK6 andAtMPK4 are activated during both abiotic and biotic stresses[36] The MAPK cascades phosphorylated OsWRKY30which enhanced the drought tolerance in rice Pointmutationof Ser in the Ser-Pro (SP) site resulted in a drought-sensitivecrop [37] This illustrates the crucial role played by MAPKphosphorylation in proper OsWRKY30 activity (Figure 1)Recent reports have characterized the presence of two pollen-specific WRKY TFs (WRKY34 and WRKY2) during malegametogenesis in Arabidopsis thaliana Overexpression ofWRKY34 using a strong pollen-specific promoter led tothe phosphorylation of the WRKY34 protein by MPK6and MPK3 [38] Mutations in the phosphorylation sites inWRKY34 compromised its functions in vivo [38] In vivophosphorylations of WRKY TFs by MAPKs have also beenrecently reported [39] The MPK3MPK6 cascade along withthe downstream WRKY TF has been depicted to induceethylene production through regulation of ACC synthaseactivity [40] The MAPK cascades involved in phosphorylat-ingWRKYs involved in abiotic stress are less studied in com-parison to the biotic counterparts However the knowledgeof these signaling cues can impose further improvements indesigning stress-tolerant transgenic crops

6 Interaction between WRKY TFs andAssociated Factors in Abiotic Stress

61 VQ Proteins VQ proteins are a group of cofactorscontaining a short VQ-related motif (FxxxVQxLTG) Out ofthe 34 VQ genes reported in Arabidopsis the majority donot contain any intron and encode small proteins of 100ndash200 amino acid residues having the consensus VQ motifIt has been reported that these 34VQ proteins can interactwith WRKY TFs in yeast [41] The VQ proteins are often


Abiotic stress drought

Receptor

MAPKKK

MAPKK

MPK3

OsWRKY30

OsWRKY30

SP

SPP

W-box

Plasma membrane

Cytoplasm

Nucleus

Figure 1 The mitogen-activated protein kinase (MAPK) pathwayinduces the activity of OsWRKY30 during drought stress Stresssignals are sensed via a transmembrane receptor which with thehelp of some unknown molecules and adaptor proteins activatesthe MPKMAPK pathway This leads to the phosphorylation andactivation of theMPK3MPK3 phosphorylates the target Ser residuein the SP motif of OsWRKY30 and activates the sameThe activatedWRKY protein then undergoes a conformational change whichfavourably allows it to bind to the W-box of its target gene toinduce transcription The protein product encoded by the targetgene probably helps the plant system in combating the droughtstress

activated byMAPK cascades in response to stress signal cuesDuring post-association with MAPK substrate1 (MKS1) VQprotein interacts with AtWRKY33 and AtWRKY25 to actas a substrate of MAPK4 [42] Interaction of VQ proteinswith WRKY TFs results in stimulation or inhibition ofthe latter to bind to its specific DNA This mainly occursbecause VQ protein binding manipulates the WRKY TFto change its preference for the nucleotides flanking theconservedW-box [43]The resulting alteration in target genespecificity of theWRKY TF gives rise to a changed biologicaldownstream response Diversification of WRKY TF-inducedresponses may also result from interactions with multipleVQ proteins [43] Tolerance to multiple abiotic stressesoccurred in Arabidopsis when the WRKY33 interacted withmultiple VQ proteins including Sigma Factor-InteractingProtein1 (SIB1) and SIB2 via the C-terminal of the WRKYdomain This interaction induced the DNA binding activityof AtWRKY33 [44] SIB1 and SIB2 have been assumed to playroles in regulation of transcription and retrograde signalingfrom chloroplast and mitochondria to the nucleus VQproteins have also been hypothesised to induce chromatinremodelling as an abiotic stress response [44] MVQ1 is

a VQ-motif-containing protein which was recently depictedto control WRKY-regulated defense gene expression [45]

62 Histone Modifying Chromatin Remodelling Complex Acondensed chromatin structure wrapped within the nucle-osomal complex in association with histone proteins andother packaging factors does not easily interact with thetranscriptional machinery So when the plant is not understress the gene remains transcriptionally silent The sensingof environmental cues signals the WRKY TFs to induce thetranscription of target stress-inducible genes The packedchromatin structure has to be loosened to facilitate properassociation of the transcription complex at the promotersite Thus it is often considered that such chromatin remod-elling complex along with autoregulation and cross regula-tion plays a crucial role in WRKY TF-induced responsesAtWRKY70 was reported to be stimulated by Arabidopsishomolog of trithorax (ATX1) and as a result the nucleoso-mal histone H3K4 trimethylation occurred [46] Epigeneticregulation by histone methyltransferase is endowed uponAtWRKY53 a senescence regulator Activation ofAtWRKY53in response to senescence triggered the rise inH3K4dimethy-lation and H3K4 trimethylation at the 51015840 end and codingregions of WRKY53 [47] In Musa acuminata the proteinencoded by the linker histone H1 gene (H1S1) interactedwith MaWRKY1 in response to the stress caused by thepostharvest ripening of fruits induced by ethyleneThe induc-tion of MaH1S1 is also accelerated in presence of jasmonicacid (JA) ABA and hydrogen peroxide and under chillingstress [48] Overexpression of AtWRKY38 and AtWRKY62enhanced the resistance of the plants to pathogenic attack byPseudomonas syringae It has been reported that the proteinsencoded by these genes interact with Histone Deacetylase 19(HD19) Overexpression of HD19 retarded the activities ofAtWRKY38 and AtWRKY62 as TFs [49]

63 Calmodulin and 14-3-3 Proteins The WRKY proteinshave a calmodulin (CaM) binding domain (CaBD) Sitedirected mutagenesis studies have confirmed the importanceof this domain in WRKY TFs to bind CaM [43] TheAtWRKY7 associated with CaM through its own CaBD TheAtWRKY7 CaBD consists of VAVNSFKKVISLLGRSR TenotherArabidopsisGroup IIdWRKYproteins have been foundto possess such related CaBDs (DxxVxKFKxVISLLxxxR)Thus these proteins also have a tendency to interact withCaMs [50] In case of overlapping WRKY-WRKY interac-tions the steric hindrance prefers WRKY-CaM interactionprovided that the calcium concentration in the cell is high[43]

SevenWRKYproteins inArabidopsishave been identifiedvia proteomic profiling of tandem affinity-purified 14-3-3complexes to interact with 14-3-3 proteins [51] Out ofthese AtWRKY6 is induced under phosphate starvationsAtWRKY18 and AtWRKY40 complexed with 14-3-3 pro-teins participate in ABA signaling [52] WRKY proteinsinteracting with 14-3-3 proteins are subjected to phospho-rylation by the latter in response to stress-activated signal-ing cascades [53] The 14-3-3 proteins are also capable ofdimerization and each dimer binds two substrates Thus


WRKY proteins with phosphorylated binding sites have thetendency to associate with other factors and proteins bymutual interactions with true 14-3-3 dimers This is the caseof indirect association of WRKY with other proteins in thecomplex [43 54] Further studies are required which will aidin developing the database of dynamic interactions of 14-3-3 proteins with WRKY TFs in the spatiotemporal context ofabiotic stress signaling cascades

7 Cross Talk between WRKY TFand ABA-Mediated Signaling

WRKY superfamily of TFs is the major regulator in plantdefence and SA-mediated signaling However significantinstances are there which show that these TFs also participatein ABA-mediated signaling [55] ABA is the universal stresshormone and the WRKY proteins associated with ABAsignaling can definitely influence stress-induced responsesAtWRKY40 has been characterised as a negative regulatorof ABA signaling during seed germination AtWRKY40 alsointeracts with AtWRKY18 and AtWRKY60 to inhibit theexpression of crucial stress-responsive genes [52] WRKY18and WRKY60 interact with the W-box of the downstreamABA Insensitive genes like ABI4 and ABI5 in order to represstheir expression [56] Utilising a stable transgenic reporter oreffector system it was observed that WRKY18 andWRKY60act as weak transcriptional activators while WRKY40 isa transcriptional repressor in plant cells [57] WRKY63 inArabidopsis is responsible for enhanced drought toleranceIncreased ABA sensitivity and reduced drought tolerancewere observed when the WRKY63ABA Overly Sensitive3(ABO3) was disrupted The drought tolerance reduced espe-cially due to unresponsive ABA-induced stomatal closureAtWRKY63 binds to the promoters of ABA Responsive Ele-ment Binding ProteinsFactors (AREB1ABF2) [13] Reports onthe relation betweenABA and abiotic stress-mediatedWRKYgenes have identified 16 ABA-relatedWRKY genes in rice 12of them were seen to have higher expression in response tocold drought and salinity [58] A study showed that the crosstalk between Gibberellic Acid (GA) and ABA is mediated byOsWRKY51 and OsWRKY71 in rice The expression of thegenes encoding these twoWRKYproteins is induced byABAand this results in a high ratio of OsWRKY51OsWRKY71repressors to GAMYB activator [59] GA induction of 120572-amylase promoter (Amy32b) is suppressed due to the bindingof OsWRKY51OsWRKY71 repressors with the respectiveW-boxes In such a situation GA induces the productionof GAMYB and inhibits OsWRKY51 and OsWRKY71 Dueto higher levels of GAMYB the 120572-amylase gene expressionincreases [59] Other activators of 120572-amylase gene expres-sion via GA are protein factors like OsDOF3 RAMY andOsMYBs1OsMYBS2 The repressors other than those men-tioned above are KGM and HRT [59 60]

Larrea tridentata (creosote bush) due to its xerophyticevergreen nature has very high tolerance towards droughtWRKY21 of 314 amino acid residues with localization in thenucleus has been isolated from the creosote bush LtWRKY21binds to the promoter of ABA-responsive gene HVA22 and

promotes transcription of the same This activation of tran-scription is dependent on the levels of LtWRKY21 [61] TheHVA22 protein has important roles in combating multipleabiotic stresses High gene expression occurs due to coexpres-sion of activators likeVP1 andABA Insensitive5 (ABI5) alongwith LtWRKY21 The dominant negative mutant proteinphosphatases like abi1-1 are not inhibitors of LtWRKY21VP1 and ABI5 coexpression though these mutant phos-phatases are negative regulators of ABA signalingThis provesthe fact that the complex of LtWRKY21 VP1 and ABI5obviously regulates downstream of ABI1 in ABA-mediatedresponse cascades during abiotic stress [61] AtWRKY57has shown enhanced expression in response to higher ABAlevels conferring higher drought tolerance to the plant [62]Chromatin immunoprecipitation (ChIP) assays confirmedthe binding of WRKY57 to the W-box of Responsive to Des-iccation 29A (RD29A) and 9-cis-epoxycarotenoid dioxygenase3 (NCED3) promoters Thus WRKY57 functions by directlyinducing stress-responsive genes [62] In rice OsWRKY45-1 and OsWRKY45-2 participate in ABA-mediated responsesduring abiotic stress OsWRKY45-2 had a negative effect onABA-induced downstream responses to salt stressThese twoWRKY proteins have also been proved to regulate ABA-dependent signaling during drought and low temperaturestresses [63] WRKY proteins can act both as activators andrepressors to ABA-inducible promoters OsWRKY24 andOsWRKY45 act as the repressors while OsWRKY72 andOsWRKY77 act as the activators [64] WRKY TFs havealso been reported to upregulate ABA-responsive genes likeABF4 ABI4 MYB2 Dehydration Response Element BindingProtein 1a (DREBP1a) DREBP2a and Response to ABA18 (RAB18) Several WRKY TFs have been reported tobe positive regulators of ABA-mediated stomatal closurewhile some are negative regulators of seed germination andalso indirectly control flowering [65] In ABA-treated salt-tolerant rice variety Pokkali the expression of WRKY71increased while feeble induction was reported for WRKY24[66] Recent findings showed that the expression of WRKY8was downregulated by the crucifer-infecting tobacco mosaicvirus (TMV-cg) In the systemically infected leaves of thewrky8 mutants the expression of ABI4 was reduced whilethat of 1-aminocyclopropane-1-carboxylic acid synthase 6(ACS6) and the ethylene response factor 104 (ERF104) wasenhanced The accumulation of TMV-cg was reduced onexogenous application of ABA [67] WRKY20 isolated fromGlycine soja was characterized to regulate ABA signaling andenhance drought tolerance The GsWRKY20 has also beenreported to be associated with flowering with high expressionin the shoot tips and the inflorescence meristems of wildsoybean [68]

8 Transgenic Approaches for Overexpressionof WRKY Proteins during Abiotic Stress

81 Drought and Salinity Stresses Prolonged drought in aparticular area results in a physically dry soil which isunsuitable for crop productivity On the other hand highsalt concentration gives rise to a physiologically dry soil


Oxidative Cold

Drought Light

Sugar starvation

Pi starvation

Salinity

OsWRKY11 AtWRKY34

AtWRKY25

AtWRKY6

AtWRKY28

AtWRKY26AtWRKY33

AtWRKY8

AtWRKY48

AtWRKY30

AtWRKY57

TcWRKY53

GmWRKY54

Heat

PtrWRKY2

TaWRKY10

AtWRKY75

VvWRKY55

BcWRKY46GmWRKY21

AtWRKY45

HvWRKY46

AtWRKY40

Radiation

OsWRKY89

Abiotic stress

Figure 2 WRKY proteins regulating plant responses against multiple abiotic stresses like salinity drought heat cold nutrient starvationlight radiation and oxidative stresses ldquoAtrdquo refers toArabidopsis thaliana ldquoOsrdquo refers toOryza sativa ldquoGmrdquo refers toGlycinemax ldquoVvrdquo refers toVitis vinifera ldquoHvrdquo refers toHordeum vulgare ldquoTardquo refers to Triticum aestivum ldquoBcrdquo refers to Brassica campestris and ldquoPtrrdquo refers to Poncirustrifoliata

which is also antagonistic for sustainability of the cropsThus drought and salinity stresses merge at a commonpoint of water shortage thus inhibiting crop productivityThis is the reason for which most of the WRKY protein-mediated responses for both stresses are very commonin nature Since the response is overlapping it becomesdifficult to divide the WRKY proteins into a particular groupresponsible for drought tolerance and another responsible forsalt tolerance [69] Under the control of HSP101 promoterthe overexpression of OsWRKY11 resulted in lower rates ofleaf-wilting and enhanced chlorophyll stability along withsustenance of the green partsThese factors help in generatinghigher drought tolerance in the crop [70] (Figure 2) The35S OsWRKY45 and 35S OsWRKY72 Arabidopsis plantshad higher expression of the ABA-inducible genes whichaided in developing higher salt and drought tolerance inthe plant [71] Overexpression of GmWRKY54 from Glycinemax in transgenic lines enhanced the salt and droughttolerance (Figure 2) High levels of GmWRKY54 are thoughtto manipulate the expression of the TF gene salt toleranceZn finger (STZZat10) and DREB2A The transgenic plantsoverexpressing the GmWRKY13 had decreased sensitivity toABA while these plants had less tolerance towards high saltand mannitol in comparison to the wild types Thus it canbe inferred that GmWRKY13 is a negative regulator of abioticstress response when overexpressed alone [72] Exposure tosalt and drought stress induced the expression of TcWRKY53in Thlaspi caerulescens Two ethylene response factor (ERF)

family genes in tobacco NtERF5 and NtEREBP-1 had lowtranscription levels in transgenic tobacco plants overexpress-ing TcWRKY53 [73] The expression of the Late Embryo-genesis Abundant (LEA) family gene NtLEA5 remainedunaffected indicating the fact that TcWRKY53 increasesosmotic stress tolerance through interaction with an ERF-type TF It is probable that TcWRKY53 does not directlymanipulate the stress-responsive genes [73] Overexpressionof either AtWRKY25 or AtWRKY33 conferred salt tolerancein Arabidopsis These two WRKY proteins are closely relatedand their transcript levels subsequently increased when theplants were treated with high concentrations of salt Theimportance of these proteins was proved from a mutationexperiment considering Atwrky33 null mutants and doublemutants of Atwrky25 and Atwrky33 Both types of mutantsexhibited increased sensitivity to saline stress [34] Arrest ofseed germination under the influence of ABA is levied byAtWRKY2 which has been proposed to act as a negativefeedback regulator of ABA-induced seed dormancy [74]AtWRKY57 AtWRKY8 and AtWRKY28 regulate signalingcascades in salinity drought osmotic and oxidative stresses[75] (Figure 2)

Results furnished by suitable experiments showed thateight out of 15 WRKY genes in wheat are induced by highsalt concentrations PEG cold or heat [29] Overexpressionof OsWRKY30 activated by a MAPK cascade enhanced thetolerance of transgenic rice to drought [40] The salt anddrought tolerance dramatically increased when TaWRKY10


from wheat was introduced and overexpressed in tobaccoTaWRKY10 has been depicted as a major TF activating mul-tiple stress-related genes and also has a role in maintainingthe osmotic balance in the cell The transgenic tobacco linesexhibited remarkably high levels of proline and soluble sugarbut low levels of malondialdehyde (MDA) when exposedto drought or salt stress [76] TaWRKY2 and TaWRKY19overexpression in Arabidopsis led to more efficient saltdrought and low temperature tolerance The overexpressionof BcWRKY46 and HvWRKY38 in Arabidopsis resulted inenhanced tolerance towards drought and salt stresses [76]The protein products of these genes are nuclear proteinsand act as TFs targeting many downstream genes whichneed to be activated to combat abiotic stress [77] Exposureof Arabidopsis to salinity stress resulted in twofold increasein the levels of 18 WRKY transcripts and repression ofeight WRKY genes [58] We have already discussed theinduction of ABA-responsive genes due to the AtWRKY40-ABAR (ABA-binding protein) interaction AtWRKY18 andAtWRKY60 act in synchronization to increase the sensi-tivity of the plant towards salt and osmotic stresses [14]The expression of PtrWRKY2 gene in Poncirus trifoliatawas suppressed by 27ndash50 upon exposure to prolongeddrought stress However in drought-stressed Citrus maxima(pummelo) plants the expression pattern of PtrWRKY2remained unaltered [78] Salt and ABA treatment increasedthe transcript levels of OsWRKY08 Osmotic stress tolerancevia positive regulation of two ABA-dependent genes likeAtCOR47 andAtRD21was reported in transgenicArabidopsisoverexpressing OsWRKY08 [24] Recent reports highlightedthe upregulation of AtWRKY46 during osmotic stresses likesalinity and drought The roles of WRKY46 in mediatingcellular osmoprotection and redox homeostasis under stresshave also been depicted via microarray analysis Regula-tion of light-dependent starch metabolism is performed byWRKY46 through the control of the QUA-QUINE STARCH(QQS) gene expression [79] The group II family of WRKYTFs (JcWRKY) found in the biofuel crop Jatropha curcasdeveloped tolerance against ionic osmotic and chemicalstresses when expressed in E coli Transcript analysis showedthat transcription of JcWRKY was increased in responseto salinity dehydration salicylic acid methyl jasmonateand the collar rot fungus Macrophomina [80] In cotton(Gossypium hirsutum) a Group IIdWRKY gene GhWRKY17was found to be associated with salt and drought stressIncreased drought and salt sensitivity resulted in trans-genic tobacco plants (Nicotiana benthamiana) overexpressingGhWRKY17 GhWRKY17 lowered ABA sensitivity leadingto low transcription of ABA-inducible genes like AREBDREB NCED ERD and LEA [81] These instances obviouslyindicate the enormous influence of the WRKY proteins inactivating a proper response against salt and dehydrationThe plants which appear to be tolerant under these harm-ful environmental circumstances show persistence of greenpartsThis has been obviously due to shielding of chlorophylland other necessary pigments required for photosynthesisThus the WRKY TFs must be playing crucial roles inguarding these pigments against the low water status of thecell and preventing influx of salt beyond the threshold limits

The content of Reactive Oxygen Species (ROS) in the tissuesof the tolerant varieties is also low [82 83] 61 WRKY geneswere identified inPopuluswhichwere induced by both abioticand biotic treatments like infectionwithMarssonina brunneaSA methyl jasmonate wounding cold and salinity 46 genesfrom this cluster were shown to be expressed in roots stemsand leaves [84]These results probably hint towards the role ofWRKY TFs as activators of genes encoding LEA proteins likedehydrins or even some genes in the biosynthetic pathwaysof compatible solutes like proline polyamines and so forth

82 Oxidative Stress WRKY has often been depicted asan aggravator of ROS production in cells The ROSlike superoxide hydroxyl radicals and hydrogen perox-ide have tremendous negative impact on the concernedcell wall leading to lipid peroxidation cell damage andoxidative stress The uptake of oxygen is responsible forsuch oxidative burst of ROS [82 85] Hydrogen per-oxide treatment in Arabidopsis triggered higher expres-sion of AtWRKY30 AtWRKY75 AtWRKY48 AtWRKY39AtWRKY6 AtWRKY53 AtWRKY22 and AtWRKY08 [86](Figure 2) The WRKY proteins also help in quenchingthe ROS produced in mitochondria The changes in envi-ronmental conditions and retrograde signaling affect theexpression of several nuclear genes encoding mitochon-drial proteins About 72 WRKY proteins in Arabidopsisgenome have been proved to regulate production of nucleartranscripts encoding mitochondrial proteins These WRKYproteins do have WRKY domains complementary to theW-box at the promoters on the nuclear transcripts [87]WRKY binds to the promoters of marker genes like Alter-native oxidase1a (AOX1a) NADH dehydrogenase B2 andthe AAA ATPase Ubiquinol-cytochrome c reductase syn-thesis1 The effects of antimycin A-induced mitochondrialretrograde expression and high light-induced stress werereduced by the overexpression of AtWRKY40 [88] On thecontrary AtWRKY63 acts as an activator in inducing highlight stress tolerance It can be assumed that high light-induced stress leads to the formation of ROS which can besomehow quenched by downstream responses triggered byAtWRKY63 Coordination in the coding of stress-responsivegenes in mitochondria and chloroplast has been studiedthrough the functions of AtWRKY40 and AtWRKY63Theseproteins regulate the expression of stress-responsive genescommon to both mitochondria and chloroplasts withoutdisturbing the constitutive expression of the house-keepinggenes in other organelles [87] Another instance of WRKYproteins involved in oxidative and light stress is the T-DNAknockout mutant of APX1 gene which led to the induc-tion of AtWRKY6 AtWRKY18 AtWRKY25 AtWRKY33AtWRKY40 AtWRKY46 AtWRKY54 AtWRKY60 andAtWRKY70 [13] AtWRKY70 exhibited constitutive expres-sion in the Atapx1 mutants [89] Thus WRKY proteinsindirectly do help in the scavenging of ROS in order toalleviate oxidative stress

The key proponents of the ROS signaling cascade areascorbate peroxidases (APX) NADPH oxidases and Zn fin-ger proteins Researchers have proposed the relation betweenZn finger proteins and WRKY factors in alleviating ROS


toxicity AtWRKY25 could not be formed in appropriateamounts inAtzat12mutant (gene for Zn finger protein) plantsexposed to high levels of hydrogen peroxide Thus it canbe obviously suggested that the expression of AtWRKY25is dependent on the protein encoded by AtZat12 [90] TheTF TaWRKY10 of wheat when overexpressed in transgenictobacco decreased the accumulation ofMDAand lowered thelevels of superoxide radical and hydrogen peroxide formationon exposure to salinity and drought stresses Low MDA wasattributed to low rates of lipid peroxidation The transgenicseedlings showed increased tolerance towards oxidative stressdue to higher accumulation of TaWRKY10 [77] The trans-genic tobacco plants overexpressing GhWRKY17 exhibitedhigher sensitivity towards oxidative stress The expression ofthe genes for ROS-scavenging enzymes like APX catalase(CAT) and Superoxide Dismutase (SOD) was suppressed inthe transgenic lines [81]TheArabidopsis lines overexpressingthe TFs Helix Loop Helix17 (HLH17) andWRKY28 showedenhanced tolerance towards osmotic stress [75] WRKY30was rapidly expressed as a primary response to hydrogenperoxide and methyl viologen (MV) MV acts as a super-oxide anion propagator in light [91] Transgenic Arabidop-sis plants overexpressing WRKY15 were more sensitive toboth salinity and oxidative stresses with the formation ofincreased leaf area and accumulation of increased plantbiomass WRKY15 induced leaf area increment throughintensified endoreplication and not by extending the cellnumbers WRKY15 expressed under oxidative stress aids inthe activation of mitochondrial genes which code for pro-teins belonging to the family of mitochondrial dysfunctionregulonWRKY15 has also been proposed as a general repres-sor of genes whose products participate in mitochondrialretrograde signaling [92] During dark-induced senescencethe leaves of Pelargonium cuttings showed high accumula-tion of WRKY6 The basis of an increment in ROS leveltogether with higher expression of senescence-associatedprotease homologs PeSAG12-1 and PeWRKY6-1 could not beexplained [93] OsWRKY42 has been portrayed as a negativeregulator in oxidative stress This is because overexpressionof OsWRKY42 in rice resulted in high accumulation ofROS It was also reported that OsWRKY42 binds to theW-box of the OsMT1d (rice Metallothionein 1d) gene andrepresses its expression thereby promoting leaf senescence[94] TaWRKY10 gene isolated from Triticum aestivum wasreported to be a positive mediator of plant tolerance againstsalinity and drought through the regulation of osmoticbalance ROS scavenging and transcription of stress-relatedgenes [95]

Osmotic and oxidative stresses are linked at a point asboth decrease viability of crops in general This cross talk inthe signaling cascades of the plant in developing toleranceagainst varied abiotic stresses has obviously opened severalnew avenues of research One of them is to geneticallymodifysome particular target components in the plant system inorder to design a transgenic crop which can be tolerantto multiple abiotic stresses Our discussion gives a clearindication of the fact that WRKY proteins are emergingplayers in generating abiotic stress tolerance in cropsThoughthis group of TFs are more related to biotic stresses like

pathogen attack and plant defence their immensely growingsignificance in response to abiotic stress cannot be neglectedat all

83 Temperature Stress Physiological processes in a plantsystem are best operated at an optimum temperature Mostof these pathways are dependent on enzymes which havemaximum activity at an optimum temperature Beyond thislimit the activity of the enzymes gradually decreases asthe protein structures are affected and ultimately the entirepathway comes to a halt This is true for temperatures whichare either higher or lower than the optimum operatingtemperature of the system Several researches have beenundertaken to study the growth patterns in crops exposedto extremes of temperature This has revealed the importantroles played by WRKY proteins in response to such stresses

Tolerance to heat stress has been depicted to be regulatedby the Group I WRKY proteins AtWRKY25 AtWRKY26and AtWRKY33 (Figure 2) When the Arabidopsis plantis exposed to high temperature stress the expression ofAtWRKY33 is repressed while that of AtWRKY25 andAtWRKY26 is stimulated Inhibited seed germination lowersurvival and electrolytic leakage were seen in the heat-stressed plants having mutations at the above three lociOn the contrary increased tolerance towards heat stresswas recorded in transgenics overexpressing AtWRKY25AtWRKY26 and AtWRKY33 [34] The fact that these genesare activated by a heat-induced ethylene-dependent responsehas raised the probability of possible convergence and crosstalk between the ethylene signaling pathways and the sig-naling cascades activated in response to heat stress [34] Apossible cross talk between biotic and abiotic stress responsecomponents has also been noted in case of AtWRKY39The Arabidopsis gene AtWRKY39 is induced in response toheat stress and the WRKY protein encoded by this genepositively regulated the interaction between the SA and JAsignaling cascades [96]Heat stress has been found to regulateabout nine of the 60 analyzed WRKY genes Out of thesenine genes AtWRKY7 has been identified as a Heat ShockFactor A1a1b (HsfA1a1b) triggering the heat stress-inducedgenes [97] We have previously discussed that overexpressionof OsWRKY11 under the control of HSP101 promoter ledto increased drought tolerance It was reported that thesetransgenic plants evolved tolerance towards high temperaturestress as well [70]

AtWRKY34 expression is stimulated in response topollen-specific cold stress AtWRKY34 has been proved tobe a crucial locus in cold stress regulation as overexpressionof AtWRKY34 makes the pollens sterile even under normalgrowth conditions [98] The mutation of this gene enhancesthe cold stress tolerance in the pollens Thus AtWRKY34negatively regulates the development of cold stress tolerancein pollens This regulation is achieved by proper manip-ulation of the transcriptional activators namely C-repeatBinding Factors (CBFs) [99] Increased tolerance to coldstress has also been reported in transgenic Arabidopsis over-expressing GmWRKY21 [65] Transgenic plants overexpress-ing TaWRKY10 also showed enhanced cold stress tolerance[77] The Poncirus trifoliata WRKY gene PtrWRKY2 is an


important player in cold stress (Figure 2) The expression ofthis gene increased initially when both cold-tolerant Poncirusand cold-sensitive pummelo were exposed to cold stressHowever the gene expression subsided in both cold-tolerantPoncirus and cold-sensitive pummelo after exposure to 1hour and 1 day of cold stress respectively [78] HvWRKY38has a role in freezing tolerance as the expression of thecorresponding gene was strongly stimulated when the plantswere constantly subjected to freezing temperatures [99]Similarly PtrWRKY2 may also have some role in developingfreezing tolerance in Poncirus or pummelo In rice 41 outof 103 WRKY genes exhibited variable expression patternsin response to chilling stress [58] 25 WRKY genes inGlycine max showed differential transcription patterns inresponse to cold [72] In Vitis vinifera (grapevine) majorityof the 59 VvWRKY genes were expressed in tissues ofyoung and mature leaves tendrils stem apex roots andyoung and ripened fruits [100] The gene-chip based datawas analysed and it was reported that 36 VvWRKY geneshad their expressions increased by twofold on exposure tocold Phylogenetic studies have confirmed the possibility ofa cross talk between stress responses to salt PEG and cold-dependent VvWRKYs The VpWRKY3 is a homologous geneof VvWRKY55 On exposure to cold the levels of VpWRKY3steadily increased in the cell while VvWRKY55 expressionwas upregulated under extremely low temperatures [100]Theexpression ofVvWRKY43 increased in Solanumdulcamara inthe coldermonths [101] In the roots of barley exposed to coldtransient increase in the expression of WRKY38 occurredCold stressed Pak-choi had their BcWRKY46 genes upregu-lated Transgenic tobacco plants which exhibited constitutiveexpression of BcWRKY46 were more tolerant to cold stressin comparison to the wild type plants [102]The expression ofWRKY71 in banana peaked when the plant was treated underextremely low temperature conditions [103] Antagonisticeffects in relation to abiotic and biotic stresses were seen inrice plants with overexpressed OsWRKY76 In such plantsa specific set of Pathogenesis related (PR) genes and othergenes involved in phytoalexin synthesis after inoculationwith blast fungus were downregulated while the cold stress-associated genes like peroxidase and lipid metabolism geneswere upregulated [104]

84 Stress due to Deficiency of Nutrients Since plants aresessile organisms they are completely dependent on thenutrients and essential elements present in their rhizosphereDeficiency in an important element is strongly antagonisticto proper plant development This also leads to impairmentof multiple physiological pathways as they are always linkedat some level or through a common intermediate or cofactorSalinity or drought is actually a condition related with thecharacteristics of soil components In salinity the NaClcontent of the soil surpasses the threshold level to sustainplant growth while in drought the moisture content of thesoil is not enough to support germination or developmentNutrient deficiency also falls in the same brackets as salinityand drought This is because nutrient deficiency is also soil-related

WRKY TFs are major regulators in overcoming theadversities related to nutrient deficiency in plants grown onnutrient deficient soil (Figure 2) The first WRKY proteininvolved in nutrient deficiency was AtWRKY75 The geneencoding AtWRKY75 exhibited stimulated expression underphosphate (Pi) deficient conditions Mutations resulting insilencing of AtWRKY75 showed higher plant sensitivitytowards Pi stress accompanied with reduced absorption ofPi The AtWRKY75 RNAi plants had reduced expressionof Pi starvation-induced genes like phosphatases Mt4TPS1like genes and transporters with high affinity for transport-ing Pi [105] A negative regulator of Phosphate 1 (PHO1)expression in Arabidopsis is the AtWRKY6 The transgenicplants overexpressing AtWRKY6 were more susceptible toPi deficiency and had a similar phenotype as the Atpho1mutants This led the researchers to assume the control ofAtWRKY6 in the expression of PHO1 and this interactionwas indeed proved via ChIP-qPCR analysisThe twoW-boxesadjoining the AtPHO1 promoter are responsible for properbinding of AtWRKY6 through itsWRKYdomain [106] It hasbeen suggested that AtWRKY75 andAtWRKY6 differentiallyand cooperatively regulate the responses to Pi deficiencyAtWRKY6 also acts as a positive mediator of plant responsesduring boron deficiency [107 108] AtWRKY45 is mainlylocalized in the nucleus The concentration of AtWRKY45peaked in the roots typically facing Pi starvationAtWRKY45RNAi plants showed decreased uptake and hence loweraccumulation of Pi during Pi starvation when compared tothe wild type plants The AtWRKY45 RNAi plants were alsovery sensitive to arsenate present in the soil The expressionof Phosphate Transporter 11 (PHT11) was stimulated in thetransgenic lines overexpressing AtWRKY45 These resultshave depicted AtWRKY45 as a positive regulator in survivalagainst Pi deficiency An epistatic genetic regulation betweenAtWRKY45 and PTH11 was also reported [109 110]

Apart from positively regulating the responses to combatPi starvation WRKY45 and WRKY65 are also expressedduring carbon starvationThus theWRKY proteins encodedby these genes act as TFs to upregulate the expression ofdownstream stress-responsive genes [107 108] Increasedsensitivity to sugar starvation was reported in a transgenicArabidopsis line overexpressingWRKY72 [71]TheArabidop-sis Nucleoside Diphosphate Kinase 3a (NDPK3a) expressionis stimulated in presence of sugar and the protein encodedby the gene gets localized in the mitochondria The mito-chondrion is the chief reservoir of ATP produced mainly bythe oxidation of sugars The NDPK3a promoter has two W-boxes which aid in the binding of SUSIBA2 (HvWRKY46) inbarley plants [109 110] There are also reports of AtWRKY4and AtWRKY34 in mediating the expression of NDPK3aSUSIBA2 also regulates the expression of ISO1 and SugarResponse Element IIb (SREIIb) in sugar signaling [109 110]Further researches and critical analyses are yet to be madeon the queer role of WRKY proteins connecting the plantresponses to tackle Pi and sugar starvation This link maybe an indication towards a beneficial symbiotic interactionbetween relative availability of Pi in the soil and sugarmetabolism [109 110]


85 Radiation Stress The least studied among all the abioticstress is the radiation stress and its associated effects on theplant system However this field is also gradually gainingenormous importance due to uneven distribution of sunlightthroughout the globe Indiscriminate uses of chlorofluoro-carbons (CFCs) and other toxic chemical compounds haveled to the formation of the ozone hole The ozone layerwhich once acted as an absolute absorber of UV radiationsis gradually losing its efficiency Thus the plants growingin areas falling under such ozone holes are more prone toUV stress This is where the significance of designing plantsresistant to radiation stress lies

Radiation stress mainly induces the bleaching of photo-synthetic pigments and generation of ROS Thus theWRKYgenes which encode proteins involved in scavenging of ROSobviously get upregulated We have already discussed thesegenes which regulate oxidative stress in plants Howevera WRKY gene OsWRKY89 was identified in rice whichhas been depicted to regulate responses during UV-B stress(Figure 2) Increased wax deposition on the surfaces of leaveswas reported in UV-B stressed transgenic plants overex-pressing OsWRKY89 [111] The increased wax depositiondrastically reduced the percentage of UV-B transmittancethrough the leaves Further researches are required to createa database on the involvement of multiple WRKY proteinsregulating the responses induced by radiation stress

9 Conclusion

In this review we emphasized the most recent advanceson WRKY proteins WRKY proteins have been thought tohave more significance in regulating biotic stress responseas compared to abiotic stress However modern researchworks and trailblazing experiments have proved their pivotalroles for developing plant tolerance towards abiotic stressWRKY proteins have several interacting partners whichtogether coordinate multiple signal cascades The relationbetween MAPKs and WRKY proteins also indicates a coop-erative signal transduction cascadeTheABA-inducible genesinvolved in abiotic stress responses are also dependent ontheir activation byMAPKs or sometimesCalciumDependentProtein Kinases (CDPKs) A potential cross talk betweenthe MAPKs activating WRKY TFs and those upregulat-ing the abiotic stress response gene is yet to be reportedImproved technologies along with molecular computationaland informational agrobiology may furnish further detailsin this respect in near future Future prospects in this fieldalso include the possibility of a cross talk between abioticand biotic stress responses mediated by WRKY factors Thestructurally related proteins AtWRKY18 AtWRKY40 andAtWRKY60 have provided some hint towards the occurrenceof such cross talk (Figure 3) This is because these proteinsare participants in the pathways regulated by the three majorphytohormones of plant system that is SA JA andABA [14]While SA and JA are involved in transducing response againstbiotic stress ABA is an essential proponent in the abioticstress pathways WRKY18 WRKY40 and WRKY60 also actas an activator of the IaaH (indole-3-acetamide hydrolase)and IaaM (tryptophan monooxygenase) genes of the T-DNA

Biotic stress Abiotic stress

AtWRKY18 AtWRKY40 AtWRKY60

Regulate biotic stress

responses

Regulate abiotic stress

responses

SA JA

ABA

SA JA

ABASA JA

ABA

Figure 3 Specific WRKY proteins like AtWRKY18 AtWRKY40and AtWRKY60 have been depicted as mediators of cross talkbetween plant responses against abiotic and biotic stresses It hasbeen reported that these proteins get accumulated in response toSA and JA during biotic stress as well as ABA during abiotic stressresponses

after its integration in the plant following Agrobacteriuminfection Thus WRKYs play a role in the expression ofthe oncogenes and inducing crown gall disease [112] InPopulus tomentosa overexpression of Group IIaWRKY genePtoWRKY60 resulted in the upregulation of the PR51 PR52PR54 PR55 and other defense-associated genes [113] Dou-ble mutants ofWRKY18 andWRKY40 enhanced Arabidopsisresistance against powdery mildew fungus Golovinomycesorontii by transcriptional reprogramming alterations in theSA or JA signalling and Enhanced Disease Susceptibility1(EDS1) expression along with accumulation of camalexin Itwas further hypothesised that this fungus required the twoWRKY proteins for successful infection [114 115] Anotherinstance of a cross talk between abiotic and biotic stressresponses is the function of AtWRKY25 and AtWRKY33These proteins show accumulation both under abiotic andbiotic stresses Abiotic stresses like NaCl and high tem-perature or pathogenic invasion by Pseudomonas syringaeinduced the expression of AtWRKY25 and AtWRKY33 [116]Future prospects also involve the possible identification ofspecific WRKY proteins which can develop plant toleranceagainst multiple abiotic stresses An example of a WRKYprotein in this context is theAtWRKY8which upregulates theplant tolerance against salinity drought and also oxidativestress (Figure 2) Genetic engineers can target such singleWRKY factors and design multistress tolerant transgenicplant lines Such tolerant lines can be designed in cereal foodcrops like rice Seeds of such crops can be distributed tofarmers acrosswide geographical areas for compatible growtheven under harsh environmental conditions

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper


Acknowledgments

Financial assistance from Science and Engineering ResearchBoard (SERB) Department of Science and Technology Gov-ernment of India through the research grant (SRFTLS-652010) and from Council of Scientific and IndustrialResearch (CSIR) Government of India through the researchgrant (38(1387)14EMR-II) to Dr Aryadeep Roychoudhuryis gratefully acknowledged

References

[1] A Matsui J Ishida T Morosawa et al ldquoArabidopsis transcrip-tome analysis under drought cold high-salinity andABA treat-ment conditions using a tiling arrayrdquo Plant and Cell Physiologyvol 49 no 8 pp 1135ndash1149 2008

[2] V Chinnusamy K Schumaker and J-K Zhu ldquoMoleculargenetic perspectives on cross-talk and specificity in abioticstress signalling in plantsrdquo Journal of Experimental Botany vol55 no 395 pp 225ndash236 2004

[3] A RoyChoudhury B Gupta andDN Sengupta ldquoTrans-actingfactor designated OSBZ8 interacts with both typical abscisicacid responsive elements as well as abscisic acid responsiveelement-like sequences in the vegetative tissues of indica ricecultivarsrdquo Plant Cell Reports vol 27 no 4 pp 779ndash794 2008

[4] D M Riano-Pachon S Ruzicic I Dreyer and B Mueller-Roeber ldquoPlnTFDB an integrative plant transcription factordatabaserdquo BMC Bioinformatics vol 8 article 42 2007

[5] A Ferro Ed Abiotic Stress Role in Sustainable AgricultureDetrimental Effects and Management Strategies EnvironmentalHealthmdashPhysical Chemical and Biological Factors Nova Sci-ence New York NY USA 2014

[6] M Akhtar A Jaiswal G Taj J P Jaiswal M I Qureshi andN K Singh ldquoDREB1CBF transcription factors their structurefunction and role in abiotic stress tolerance in plantsrdquo Journalof Genetics vol 91 no 3 pp 385ndash395 2012

[7] P A Palmeros-Suarez and J P Delano-Frier ldquoThe pivotal roleplayed by transcription factors small RNAs and epigeneticmodifications in the regulation of abiotic stress responses inplantsrdquo in Abiotic Stress A Ferro Ed pp 1ndash42 Nova SciencePublishers New York NY USA 2014

[8] A Roychoudhury and A Paul ldquoAbscisic acid-inducible genesduring salinity and drought stressrdquo inAdvances inMedicine andBiology L V Berhardt Ed vol 51 pp 1ndash78 Nova Science NewYork NY USA 2012

[9] N Chen Q Yang L Pan et al ldquoIdentification of 30 MYBtranscription factor genes and analysis of their expressionduring abiotic stress in peanut (Arachis hypogaea L)rdquoGene vol533 no 1 pp 332ndash345 2014

[10] K Nakashima H Takasaki J Mizoi K Shinozaki and KYamaguchi-Shinozaki ldquoNAC transcription factors in plantabiotic stress responsesrdquoBiochimica et BiophysicaActa vol 1819no 2 pp 97ndash103 2012

[11] S Ishiguro and K Nakamura ldquoCharacterization of a cDNAencodine a novel DNA-binding protein SPF1 that recognizesSP8 sequences in the 51015840 upstream regions of genes coding forsporamin and 120573-amylase from sweet potatordquo Molecular andGeneral Genetics vol 244 no 6 pp 563ndash571 1994

[12] C P Marquez and E J Pritham ldquoPhantom a new subclass ofMutator DNA transposons found in insect viruses and widelydistributed in animalsrdquo Genetics vol 185 no 4 pp 1507ndash15172010

[13] J Li Role of WRKY Transcription Factors in ArabidopsisDevelopment and Stress Responses Helsinki University PrintingHouse Helsinki Finland 2014

[14] L Chen Y Song S Li L Zhang C Zou and D Yu ldquoTherole of WRKY transcription factors in plant abiotic stressesrdquoBiochimica et Biophysica Acta Gene Regulatory Mechanismsvol 1819 no 2 pp 120ndash128 2012

[15] Z Zou ldquoGenome-wide identification and phylogenetic analysisof WRKY transcription factor family in castor bean (Ricinuscommunis L)rdquo Chinese Journal of Oil Crop Sciences vol 35 no1 pp 36ndash42 2013

[16] K-FWei J Chen Y-F Chen L-JWu andD-X Xie ldquoMolecu-lar phylogenetic and expression analysis of the completeWRKYtranscription factor family in maizerdquo DNA Research vol 19 no2 pp 153ndash164 2012

[17] J Ling W Jiang Y Zhang et al ldquoGenome-wide analysis ofWRKY gene family in Cucumis sativusrdquo BMCGenomics vol 12article 471 2011

[18] C Cai E Niu H Du L Zhao Y Feng andW Guo ldquoGenome-wide analysis of the WRKY transcription factor gene familyin Gossypium raimondii and the expression of orthologs incultivated tetraploid cottonrdquo The Crop Journal vol 2 no 2-3pp 87ndash101 2014

[19] MWang A Vannozzi G Wang et al ldquoGenome and transcrip-tome analysis of the grapevine (Vitis vinifera L) WRKY genefamilyrdquo Horticulture Research vol 1 article 14016 2014

[20] K Yamasaki T Kigawa M Seki K Shinozaki and SYokoyama ldquoDNA-binding domains of plant-specific transcrip-tion factors structure function and evolutionrdquo Trends in PlantScience vol 18 no 5 pp 267ndash276 2013

[21] P Agarwal M P Reddy and J Chikara ldquoWRKY its struc-ture evolutionary relationship DNA-binding selectivity role instress tolerance and development of plantsrdquo Molecular BiologyReports vol 38 no 6 pp 3883ndash3896 2011

[22] T Eulgem P J Rushton S Robatzek and I E Somssich ldquoTheWRKY superfamily of plant transcription factorsrdquo Trends inPlant Science vol 5 no 5 pp 199ndash206 2000

[23] K S Alexandrova and B V Conger ldquoIsolation of two somaticembryogenesis-related genes from orchardgrass (Dactylis glom-erata)rdquo Plant Science vol 162 no 2 pp 301ndash307 2002

[24] M Lagace and D P Matton ldquoCharacterization of a WRKYtranscription factor expressed in late torpedo-stage embryos ofSolanum chacoenserdquo Planta vol 219 no 1 pp 185ndash189 2004

[25] T Ishida S Hattori R Sano et al ldquoArabidopsis TRANSPAR-ENT TESTA GLABRA2 is directly regulated by R2R3 MYBtranscription factors and is involved in regulation of GLABRA2transcription in epidermal differentiationrdquo The Plant Cell vol19 no 8 pp 2531ndash2543 2007

[26] P J Rushton I E Somssich P Ringler and Q J Shen ldquoWRKYtranscription factorsrdquo Trends in Plant Science vol 15 no 5 pp247ndash258 2010

[27] J W Borrone D N Kuhn and R J Schnell ldquoIsolationcharacterization and development of WRKY genes as usefulgenetic markers in Theobroma cacaordquo Theoretical and AppliedGenetics vol 109 no 3 pp 495ndash507 2004

[28] Y Qiu S J Jing J Fu L Li and D Yu ldquoCloning and analysisof expression profile of 13WRKY genes in ricerdquo Chinese ScienceBulletin vol 49 no 20 pp 2159ndash2168 2004

[29] H L Wu Z F Ni Y Y Yao G G Guo and Q X SunldquoCloning and expression profiles of 15 genes encoding WRKYtranscription factor in wheat (Triticum aestivem L)rdquo Progressin Natural Science vol 18 no 6 pp 697ndash705 2008


[30] Y Q Jiang and M K Deyholos ldquoComprehensive transcrip-tional profiling of NaCl-stressedArabidopsis roots reveals novelclasses of responsive genesrdquo BMC Plant Biology vol 6 article25 2006

[31] X Xu C Chen B Fan and Z Chen ldquoPhysical and functionalinteractions between pathogen-induced Arabidopsis WRKY18WRKY40 and WRKY60 transcription factorsrdquo The Plant Cellvol 18 no 5 pp 1310ndash1326 2006

[32] F Turck A Zhou and I E Somssich ldquoStimulus-dependentpromoter-specific binding of transcription factor WRKY1 toits native promoter and the defense-related gene PcPR1-1 inparsleyrdquoThe Plant Cell vol 16 no 10 pp 2573ndash2585 2004

[33] G Mao X Meng Y Liu Z Zheng Z Chen and S ZhangldquoPhosphorylation of a WRKY transcription factor by twopathogen-responsive MAPKs drives phytoalexin biosynthesisinArabidopsisrdquoThePlant Cell vol 23 no 4 pp 1639ndash1653 2011

[34] S J Li Q T Fu L G Chen W D Huang and D QYu ldquoArabidopsis thaliana WRKY25 WRKY26 and WRKY33coordinate induction of plant thermotolerancerdquo Planta vol233 no 6 pp 1237ndash1252 2011

[35] S Zhang and D F Klessig ldquoPathogen-induced MAP kinases intobaccordquoResults and Problems in Cell Differentiation vol 27 pp65ndash84 2000

[36] A Danquah A de Zelicourt J Colcombet and H Hirt ldquoTherole of ABA and MAPK signaling pathways in plant abioticstress responsesrdquo Biotechnology Advances vol 32 no 1 pp 40ndash52 2014

[37] H Shen C Liu Y Zhang et al ldquoOsWRKY30 is activatedby MAP kinases to confer drought tolerance in ricerdquo PlantMolecular Biology vol 80 no 3 pp 241ndash253 2012

[38] Y Guan X Meng R Khanna E LaMontagne Y Liu and SZhang ldquoPhosphorylation of a WRKY transcription factor byMAPKs is required for pollen development and function inArabidopsisrdquo PLoS Genetics vol 10 no 5 Article ID e10043842014

[39] N Ishihama H AdachiM Yoshioka andH Yoshioka ldquoIn vivophosphorylation of WRKY transcription factor by MAPKrdquo inPlant MAP Kinases G Komis and J Samaj Eds vol 1171 ofMethods in Molecular Biology pp 171ndash181 Springer New YorkNY USA 2014

[40] G Li X Meng R Wang et al ldquoDual-level regulation of ACCsynthase activity by MPK3MPK6 cascade and its downstreamWRKY transcription factor during ethylene induction in Ara-bidopsisrdquo PLoS Genetics vol 8 no 6 Article ID e1002767 2012

[41] Y Cheng Y Zhou Y Yang et al ldquoStructural and functionalanalysis of VQ motif-containing proteins in Arabidopsis asinteracting proteins of WRKY transcription factorsrdquo PlantPhysiology vol 159 no 2 pp 810ndash825 2012

[42] J-L Qiu B K Fiil K Petersen et al ldquoArabidopsisMAP kinase4 regulates gene expression through transcription factor releasein the nucleusrdquoTheEMBO Journal vol 27 no 16 pp 2214ndash22212008

[43] Y Chi Y Yang Y Zhou et al ldquoProtein-protein interactions inthe regulation ofWRKY transcription factorsrdquoMolecular Plantvol 6 no 2 pp 287ndash300 2013

[44] Z Lai Y Li F Wang et al ldquoArabidopsis sigma factor bindingproteins are activators of the WRKY33 transcription factor inplant defenserdquoThePlant Cell vol 23 no 10 pp 3824ndash3841 2011

[45] P Pecher L Eschen-Lippold S Herklotz et al ldquoThe arabidopsisthaliana mitogen-activated protein kinases MPK3 and MPK6target a subclass of lsquoVQ-motif rsquo-containing proteins to regulate

immune responsesrdquo New Phytologist vol 203 pp 592ndash6062014

[46] R Alvarez-Venegas A A Abdallat M Guo J R Alfano and ZAvramova ldquoEpigenetic control of a transcription factor at thecross section of two antagonistic pathwaysrdquo Epigenetics vol 2no 2 pp 106ndash113 2007

[47] N Ay K Irmler A Fischer R Uhlemann G Reuter and KHumbeck ldquoEpigenetic programming via histone methylationat WRKY53 controls leaf senescence in Arabidopsis thalianardquoPlant Journal vol 58 no 2 pp 333ndash346 2009

[48] J-N Wang J-F Kuang W Shan et al ldquoExpression profiles of abanana fruit linker histone H1 geneMaHIS1 and its interactionwith a WRKY transcription factorrdquo Plant Cell Reports vol 31no 8 pp 1485ndash1494 2012

[49] K-C Kim Z Lai B Fan and Z Chen ldquoArabidopsis WRKY38and WRKY62 transcription factors interact with histonedeacetylase 19 in basal defenserdquo The Plant Cell vol 20 no 9pp 2357ndash2371 2008

[50] C Y Park J H Lee J H Yoo et al ldquoWRKY group IIdtranscription factors interact with calmodulinrdquo FEBS Lettersvol 579 no 6 pp 1545ndash1550 2005

[51] I-F ChangA Curran RWoolsey et al ldquoProteomic profiling oftandem affinity purified 14-3-3 protein complexes in Arabidop-sis thalianardquo Proteomics vol 9 no 11 pp 2967ndash2985 2009

[52] Y Shang L Yan Z-Q Liu et al ldquoThe Mg-chelatase H subunitof Arabidopsis antagonizes a group of WRKY transcriptionrepressors to relieve ABA-responsive genes of inhibitionrdquo ThePlant Cell vol 22 no 6 pp 1909ndash1935 2010

[53] Y H Shen J Godlewski A Bronisz et al ldquoSignificance of14ndash3ndash3 self-dimerization for phosphorylation-dependent targetbindingrdquo Molecular Biology of the Cell vol 14 no 11 pp 4721ndash4733 2003

[54] A Arulpragasam A L Magno E Ingley et al ldquoThe adaptorprotein 14-3-3 binds to the calcium-sensing receptor and atten-uates receptor-mediated Rho kinase signallingrdquo BiochemicalJournal vol 441 no 3 pp 995ndash1006 2012

[55] J Dong C Chen and Z Chen ldquoExpression profiles of theArabidopsis WRKY gene superfamily during plant defenseresponserdquo Plant Molecular Biology vol 51 no 1 pp 21ndash37 2003

[56] Z-Q Liu L Yan Z Wu et al ldquoCooperation of threeWRKY-domain transcription factors WRKY18 WRKY40 andWRKY60 in repressing two ABA-responsive genes ABI4 andABI5 in Arabidopsisrdquo Journal of Experimental Botany vol 63no 18 pp 6371ndash6392 2012

[57] H Chen Z Lai J Shi Y Xiao Z Chen and X Xu ldquoRolesofArabidopsisWRKY18WRKY40 andWRKY60 transcriptionfactors in plant responses to abscisic acid and abiotic stressrdquoBMC Plant Biology vol 10 article 281 2010

[58] R Ramamoorthy S-Y Jiang N Kumar P N Venkatesh andS Ramachandran ldquoA comprehensive transcriptional profilingof the WRKY gene family in rice under various abiotic andphytohormone treatmentsrdquo Plant and Cell Physiology vol 49no 6 pp 865ndash879 2008

[59] Z Xie Z-L Zhang X Zou G Yang S Komatsu and Q JShen ldquoInteractions of two abscisic-acid induced WRKY genesin repressing gibberellin signaling in aleurone cellsrdquo The PlantJournal vol 46 no 2 pp 231ndash242 2006

[60] R Peng Q Yao A Xiong et al ldquoA new rice zinc-finger proteinbinds to theO2S box of the120572-amylase gene promoterrdquoEuropeanJournal of Biochemistry vol 271 no 14 pp 2949ndash2955 2004


[61] X Zou J R Seemann D Neuman and Q J Shen ldquoA WRKYgene from creosote bush encodes an activator of the abscisicacid signaling pathwayrdquoThe Journal of Biological Chemistry vol279 no 53 pp 55770ndash55779 2004

[62] Y Jiang G Liang and D Yu ldquoActivated expression ofWRKY57confers drought tolerance in ArabidopsisrdquoMolecular Plant vol5 no 6 pp 1375ndash1388 2012

[63] Z Tao Y Kou H Liu X Li J Xiao and S Wang ldquoOsWRKY45alleles play different roles in abscisic acid signalling and saltstress tolerance but similar roles in drought and cold tolerancein ricerdquo Journal of Experimental Botany vol 62 no 14 pp 4863ndash4874 2011

[64] Z Xie P Ruas and Q J Shen ldquoRegulatory networks of thephytohormone abscisic acidrdquo Vitamins and Hormones vol 72pp 235ndash269 2005

[65] D L Rushton P Tripathi R C Rabara et al ldquoWRKY transcrip-tion factors key components in abscisic acid signallingrdquo PlantBiotechnology Journal vol 10 no 1 pp 2ndash11 2012

[66] S Basu and A Roychoudhury ldquoExpression profiling of abioticstress-inducible genes in response to multiple stresses in rice(Oryza saltiva L) varieties with contrasting level of stresstolerancerdquo BioMed Research International vol 2014 Article ID706890 12 pages 2014

[67] L Chen L Zhang D Li F Wang and D Yu ldquoWRKY8transcription factor functions in the TMV-cg defense responseby mediating both abscisic acid and ethylene signaling inArabidopsisrdquo Proceedings of the National Academy of Sciences ofthe United States of America vol 110 no 21 pp E1963ndashE19712013

[68] X Luo X Sun B Liu et al ldquoEctopic expression of a WRKYhomolog fromGlycine soja alters flowering time inArabidopsisrdquoPLoS ONE vol 8 no 8 Article ID e73295 2013

[69] D Golldack I Luking andO Yang ldquoPlant tolerance to droughtand salinity stress regulating transcription factors and theirfunctional significance in the cellular transcriptional networkrdquoPlant Cell Reports vol 30 no 8 pp 1383ndash1391 2011

[70] X Wu Y Shiroto S Kishitani Y Ito and K ToriyamaldquoEnhanced heat and drought tolerance in transgenic riceseedlings overexpressing OsWRKY11 under the control ofHSP101 promoterrdquo Plant Cell Reports vol 28 no 1 pp 21ndash302009

[71] Y Song L G Chen L P Zhang and D Q Yu ldquoOverexpressionof OsWRKY72 gene interferes in the abscisic acid signal andauxin transport pathway of Arabidopsisrdquo Journal of Biosciencesvol 35 no 3 pp 459ndash471 2010

[72] Q-Y Zhou A-G Tian H-F Zou et al ldquoSoybean WRKY-type transcription factor genes GmWRKY13 GmWRKY21 andGmWRKY54 confer differential tolerance to abiotic stresses intransgenic Arabidopsis plantsrdquo Plant Biotechnology Journal vol6 no 5 pp 486ndash503 2008

[73] W Wei Y X Zhang L Han Z Q Guan and T Y Chai ldquoAnovel WRKY transcriptional factor from Thlaspi caerulescensnegatively regulates the osmotic stress tolerance of transgenictobaccordquo Plant Cell Reports vol 27 no 4 pp 795ndash803 2008

[74] W B Jiang and D Q Yu ldquoArabidopsis WRKY2 transcriptionfactor may be involved inosmotic stress responserdquo Acta Botan-ica Yunnanica vol 31 no 5 pp 427ndash432 2009

[75] K C Babitha S V Ramu V Pruthvi P Mahesh K NNataraja and M Udayakumar ldquoCo-expression of AtbHLH17andAtWRKY28 confers resistance to abiotic stress inArabidop-sisrdquo Transgenic Research vol 22 no 2 pp 327ndash341 2013

[76] Y Wang F Dang Z Liu et al ldquoCaWRKY58 encoding agroup IWRKY transcription factor ofCapsicum annuum nega-tively regulates resistance to Ralstonia solanacearum infectionrdquoMolecular Plant Pathology vol 14 no 2 pp 131ndash144 2013

[77] C-F Niu W Wei Q-Y Zhou et al ldquoWheat WRKY genesTaWRKY2 and TaWRKY19 regulate abiotic stress tolerance intransgenicArabidopsis plantsrdquoPlant Cell andEnvironment vol35 no 6 pp 1156ndash1170 2012

[78] M Sahin-Cevik ldquoA WRKY transcription factor gene isolatedfrom Poncirus trifoliata shows differential responses to cold anddrought stressesrdquoPlant Omics Journal vol 5 no 5 pp 438ndash4452012

[79] Z J Ding J Y Yan X Y Xu et al ldquoTranscription factorWRKY46 regulates osmotic stress responses and stomatalmovement independently inArabidopsisrdquo Plant Journal vol 79no 1 pp 13ndash27 2014

[80] P Agarwal M Dabi and P K Agarwal ldquoMolecular cloningand characterization of a group II WRKY transcription factorfrom Jatropha curcas an important biofuel croprdquoDNA and CellBiology vol 33 no 8 pp 503ndash513 2014

[81] H Yan H Jia X Chen L Hao H An and X Guo ldquoThe cottonWRKY transcription factor GhWRKY17 functions in droughtand salt stress in transgenic Nicotiana benthamiana throughABA signaling and the modulation of reactive oxygen speciesproductionrdquo Plant and Cell Physiology vol 55 no 12 pp 2060ndash2076 2014

[82] K Das and A Roychoudhury ldquoReactive oxygen species (ROS)and response of antioxidants as ROS-scavengers during envi-ronmental stress in plantsrdquo Frontiers in Environmental Sciencevol 2 article 53 13 pages 2014

[83] A Banerjee and A Roychoudhury ldquoMetabolic engineering oflipids in plantsrdquo Journal of Plant Science and Research vol 1 pp1ndash20 2014

[84] Y Jiang Y Duan J Yin et al ldquoGenome-wide identificationand characterization of the PopulusWRKY transcription factorfamily and analysis of their expression in response to biotic andabiotic stressesrdquo Journal of Experimental Botany vol 65 no 22pp 6629ndash6644 2014

[85] A Roychoudhury and K Das ldquoFunctional role of polyaminesand polyamine-metabolizing enzymes during salinity droughtand cold stressesrdquo inPlantAdaptation to Environmental ChangeN A Anjum S S Gill and R Gill Eds CAB InternationalLondon UK 2014

[86] L G Chen L P Zhang and D Q Yu ldquoWounding-inducedWRKY8 is involved in basal defense in Arabidopsisrdquo MolecularPlant-Microbe Interactions vol 23 no 5 pp 558ndash565 2010

[87] O van Aken B Zhang S Law R Narsai and J WhelanldquoAtWRKY40 and AtWRKY63 modulate the expression ofstress-responsive nuclear genes encoding mitochondrial andchloroplast proteinsrdquo Plant Physiology vol 162 no 1 pp 254ndash271 2013

[88] B Zhang C Carrie A Ivanova et al ldquoLETM proteins play arole in the accumulation of mitochondrially encoded proteinsin Arabidopsis thaliana and AtLETM2 displays parent of origineffectsrdquoThe Journal of Biological Chemistry vol 287 no 50 pp41757ndash41773 2012

[89] S Ciftci-Yilmaz M R Morsy L Song et al ldquoThe EAR-motif ofthe Cys2His2-type zinc finger protein Zat7 plays a key role inthe defense response of Arabidopsis to salinity stressrdquo Journal ofBiological Chemistry vol 282 no 12 pp 9260ndash9268 2007

[90] L Rizhsky S Davletova H Liang and R Mittler ldquoThe zinc fin-ger protein Zat12 is required for Cytosolic Ascorbate Peroxidase


1 expression during oxidative stress in ArabidopsisrdquoThe Journalof Biological Chemistry vol 279 no 12 pp 11736ndash11743 2004

[91] T E Scarpeci M I Zanor N Carrillo B Mueller-Roeber andE M Valle ldquoGeneration of superoxide anion in chloroplasts ofArabidopsis thaliana during active photosynthesis a focus onrapidly induced genesrdquo Plant Molecular Biology vol 66 no 4pp 361ndash378 2008

[92] S Vanderauwera K Vandenbroucke A Inze et al ldquoAtWRKY15perturbation abolishes the mitochondrial stress response thatsteers osmotic stress tolerance inArabidopsisrdquoProceedings of theNational Academy of Sciences of theUnited States of America vol109 no 49 pp 20113ndash20118 2012

[93] S Rosenvasser S Mayak and H Friedman ldquoIncrease inreactive oxygen species (ROS) and in senescence-associatedgene transcript (SAG) levels during dark-induced senescenceof Pelargonium cuttings and the effect of gibberellic acidrdquo PlantScience vol 170 no 4 pp 873ndash879 2006

[94] MHan C-Y Kim J Lee S-K Lee and J-S Jeon ldquoOsWRKY42represses OsMT1d and induces reactive oxygen species and leafsenescence in ricerdquo Molecules and Cells vol 37 no 7 pp 532ndash539 2014

[95] CWang P Deng L Chen et al ldquoA wheatWRKY transcriptionfactor TaWRKY10 confers tolerance to multiple abiotic stressesin transgenic tobaccordquo PLoS ONE vol 8 no 6 Article IDe65120 2013

[96] S J Li X Zhou L G Chen W D Huang and D Q YuldquoFunctional characterization of Arabidopsis thaliana WRKY39in heat stressrdquo Molecules and Cells vol 29 no 5 pp 475ndash4832010

[97] W Busch M Wunderlich and F Schoffl ldquoIdentification ofnovel heat shock factor-dependent genes and biochemicalpathways in Arabidopsis thalianardquo Plant Journal vol 41 no 1pp 1ndash14 2005

[98] C Zou W Jiang and D Yu ldquoMale gametophyte-specificWRKY34 transcription factor mediates cold sensitivity ofmature pollen in Arabidopsisrdquo Journal of Experimental Botanyvol 61 no 14 pp 3901ndash3914 2010

[99] C Mare E Mazzucotelli C Crosatti E Francia A M Stancaand L Cattivelli ldquoHv-WRKY38 a new transcription factorinvolved in cold- and drought-response in barleyrdquo Plant Molec-ular Biology vol 55 no 3 pp 399ndash416 2004

[100] L Wang W Zhu L Fang et al ldquoGenome-wide identificationof WRKY family genes and their response to cold stress in Vitisviniferardquo BMC Plant Biology vol 14 no 1 article 103 2014

[101] T Huang and J G Duman ldquoCloning and characterization of athermal hysteresis (antifreeze) proteinwithDNA-binding activ-ity from winter bittersweet nightshade Solanum dulcamarardquoPlant Molecular Biology vol 48 no 4 pp 339ndash350 2002

[102] F Wang X L Hou J Tang et al ldquoA novel cold-inducible genefrom Pak-choi (Brassica campestris ssp chinensis) BcWRKY46enhances the cold salt and dehydration stress tolerance intransgenic tobaccordquoMolecular Biology Reports vol 39 no 4 pp4553ndash4564 2012

[103] U K S Shekhawat T R Ganapathi and L Srinivas ldquoCloningand characterization of a novel stress-responsive WRKY tran-scription factor gene (MusaWRKY71) from Musa spp cvKaribale Monthan (ABB group) using transformed bananacellsrdquo Molecular Biology Reports vol 38 no 6 pp 4023ndash40352011

[104] N Yokotani Y Sato S Tanabe et al ldquoWRKY76 is a ricetranscriptional repressor playing opposite roles in blast disease

resistance and cold stress tolerancerdquo Journal of ExperimentalBotany vol 64 no 16 pp 5085ndash5097 2013

[105] B N Devaiah A S Karthikeyan and K G RaghothamaldquoWRKY75 transcription factor is a modulator of phosphateacquisition and root development in Arabidopsisrdquo Plant Phys-iology vol 143 no 4 pp 1789ndash1801 2007

[106] Y-F Chen L-Q LiQXu Y-HKongHWang andW-HWuldquoThe WRKY6 transcription factor modulates PHOSPHATE1expression in response to lowpi stress inArabidopsisrdquoPlantCellvol 21 no 11 pp 3554ndash3566 2009

[107] I Kasajima Y Ide M Yokota Hirai and T Fujiwara ldquoWRKY6is involved in the response to boron deficiency in Arabidopsisthalianardquo Physiologia Plantarum vol 139 no 1 pp 80ndash92 2010

[108] A L Contento S-J Kim and D C Bassham ldquoTranscriptomeprofiling of the response of Arabidopsis suspension culture cellsto Suc starvationrdquo Plant Physiology vol 135 no 4 pp 2330ndash2347 2004

[109] H Wang Q Xu Y H Kong et al ldquoArabidopsis WRKY45transcription factor activates PHOSPHATE TRANSPORTER11expression in response to phosphate starvationrdquo Plant Physiol-ogy vol 164 no 4 pp 2020ndash2029 2014

[110] M Bakshi and R Oelmuller ldquoWRKY transcription factors Jackof many trades in plantsrdquo Plant Signaling and Behavior vol 9Article ID e27700 2014

[111] H Wang J Hao X Chen et al ldquoOverexpression of riceWRKY89 enhances ultraviolet B tolerance and disease resis-tance in rice plantsrdquo Plant Molecular Biology vol 65 no 6 pp799ndash815 2007

[112] Y Zhang C-W Lee N Wehner et al ldquoRegulation of oncogeneexpression in T-DNA-transformed plant cellsrdquo PLoS Pathogensvol 11 no 1 Article ID e1004620 2015

[113] S Ye Y Jiang Y Duan et al ldquoConstitutive expression ofthe poplar WRKY transcription factor PtoWRKY60 enhancesresistance to Dothiorella gregaria Sacc in transgenic plantsrdquoTree Physiology vol 34 no 10 pp 1118ndash1129 2014

[114] M Schon A Toller C Diezel et al ldquoAnalyses ofwrky18 wrky40plants reveal critical roles of SAEDS1 signaling and indole-glucosinolate biosynthesis for Golovinomyces orontii resistanceand a loss-of resistance towards Pseudomonas syringae pvtomatoAvrRPS4rdquoMolecular Plant-Microbe Interactions vol 26no 7 pp 758ndash767 2013

[115] S P Pandey M Roccaro M Schon E Logemann and IE Somssich ldquoTranscriptional reprogramming regulated byWRKY18 andWRKY40 facilitates powderymildew infection ofArabidopsisrdquoThe Plant Journal vol 64 no 6 pp 912ndash923 2010

[116] Z Zheng S L Mosher B Fan D F Klessig and Z ChenldquoFunctional analysis of Arabidopsis WRKY25 transcriptionfactor in plant defense against Pseudomonas syringaerdquo BMCPlant Biology vol 7 article 2 2007

[117] Y Zhang and L Wang ldquoThe WRKY transcription factorsuperfamily its origin in eukaryotes and expansion in plantsrdquoBMC Evolutionary Biology vol 5 pp 1ndash12 2005

[118] Z Xie Z-L Zhang X Zou et al ldquoAnnotations and functionalanalyses of the riceWRKY gene superfamily reveal positive andnegative regulators of abscisic acid signaling in aleurone cellsrdquoPlant Physiology vol 137 no 1 pp 176ndash189 2005

[119] H Chen Z B Lai J W Shi Y Xiao Z X Chen and X PXu ldquoRoles of Arabidopsis WRKY18 WRKY40 and WRKY60transcription factors in plant responses to abscisic acid andabiotic stressrdquo BMC Plant Biology vol 10 article 281 2010


[120] Y Song S J Jing and D Q Yu ldquoOverexpression of thestress-induced OsWRKY08 improves osmotic stress tolerancein Arabidopsisrdquo Chinese Science Bulletin vol 54 no 24 pp4671ndash4678 2009


[122] H Wang J J Hao X J Chen et al ldquoOverexpression ofrice WRKY89 enhances ultraviolet B tolerance and diseaseresistance in rice plantsrdquo Plant Molecular Biology vol 65 no6 pp 799ndash815 2007

[123] Y P Qiu and D Q Yu ldquoOver-expression of the stress-inducedOsWRKY45 enhances disease resistance and drought tolerancein Arabidopsisrdquo Environmental and Experimental Botany vol65 no 1 pp 35ndash47 2009

[124] S Yu C Ligang Z Liping and Y Diqiu ldquoOverexpression ofOsWRKY72 gene interferes in the abscisic acid signal and auxintransport pathway ofArabidopsisrdquo Journal of Biosciences vol 35no 3 pp 459ndash471 2010

[125] N Ishihama and H Yoshioka ldquoPost-translational regulationof WRKY transcription factors in plant immunityrdquo CurrentOpinion in Plant Biology vol 15 no 4 pp 431ndash437 2012

[126] Y Hu Q Dong and D Yu ldquoArabidopsis WRKY46 coordi-nates with WRKY70 and WRKY53 in basal resistance againstpathogen Pseudomonas syringaerdquo Plant Science vol 185-186 pp288ndash297 2012

[127] T Wei B Ou J Li et al ldquoTranscriptional profiling of riceearly response to Magnaporthe oryzae identified OsWRKYs asimportant regulators in rice blast resistancerdquo PLoS ONE vol 8no 3 Article ID e59720 2013

[128] Z Tao H Liu D Qiu et al ldquoA pair of allelicWRKY genes playopposite roles in rice-bacteria interactionsrdquo Plant Physiologyvol 151 no 2 pp 936ndash948 2009

[129] A Lan J Huang W Zhao Y Peng Z Chen and D Kang ldquoAsalicylic acid-induced rice (Oryza sativa L) transcription factorOsWRKY77 is involved in disease resistance of Arabidopsisthalianardquo Plant Biology vol 15 no 3 pp 452ndash461 2013

[130] Y Meng and R P Wise ldquoHvWRKY10 HvWRKY19 andHvWRKY28 regulate Mla-triggered immunity and basaldefense to barley powdery mildewrdquo Molecular Plant-MicrobeInteractions vol 25 no 11 pp 1492ndash1505 2012

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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PeptidesInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

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Molecular Biology International

GenomicsInternational Journal of


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Evolutionary BiologyInternational Journal of



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Volume 2014

Stem CellsInternational



Enzyme Research



Microbiology


package of stress-induced responses like posttranslationaland epigenetic modifications namely variable nucleosomedistribution histone modification DNA methylation andsynthesis of nonprotein-coding RNAs (npcRNAs) [5]

2 TFs in Abiotic Stress

TFs have been a major target in improving stress tolerancein plants due to their ability to control critical downstreamresponses by regulating target gene transcription Entire cas-cades of signal transduction get activated when TFs interactwith specific cis-acting response elements in the promotersof stress-inducible genes This enhances combinatorial tol-erance against multiple stresses [6] Thus these TFs them-selves can be genetically upregulated to increase the stress-induced gene responsiveness and hence the overall stresstolerance The principal TFs involved in stress managementlie in the AP2ERF (Apetala2ethylene response factor) bZIP(basic leucine zipper) NAC (No Apical Meristem ATAF12Cup-Shaped Cotyledon 2) MYB C2H2 Zn finger SBP(Squamosa-Promoter Binding Protein) and WRKY (TFscontaining highly conserved WRKY domain) superfamilies[7] The bZIP TF family consists of a large number of TFswith diverse roles and ability to bind to abscisic acid- (ABA-)responsive elements (ABREs) [8] The MYB family of TFsare regulators of several responses pertaining to secondarymetabolism cell cycle biotic defence and abiotic stress [9]The NAC TFs like stress responsive NAC (SNAC) genes whenoverexpressed improve the drought tolerance in rice [10] Inthis review we will focus on the intricate relation of one ofthe largest families that is the WRKY superfamily of TFs inenhancing stress tolerance in various plant species

3 WRKY Proteins StructuralCharacterization and Classification

TheWRKY TFs were first identified in sweet potato (SPF1) asDNA-binding proteins [11] Evolution ofMutator orMutator-like transposable elements (MULEs) gave rise to the WRKY-GCM1 superfamily of Zn finger TFs [12] The TFs containingtheDNAbinding domainGCM have been clumped togetherwith the WRKY TFs to be classified as the WRKY-GCM1superfamily [13] WRKY genes are quite common in plantsthough some nonplant species have also been identifiedwhich carry such genes in their genomes 74 WRKY genesin Arabidopsis more than 100 genes in rice 197 genes insoybean 66 genes in papaya 104 genes in poplar 68 genesin sorghum 38 genes in Physcomitrella patens 35 genes inSelaginella moellendorffii 80 genes in Pinus more than 45genes in barley 56 genes in Ricinus communis 119 genes inthe B73 inbred line of maize 55 genes in Cucumis sativus120 genes in Gossypium raimondii and 59 candidate genes inVitis vinifera have been identified [14ndash19] The large numberof genes present in the genomes of several plant species doeshint about a pivotal role played by these TFs in downstreamgene activation The WRKY domain has a conserved N-terminal sequence ofWRKYGQK along with a Zn finger-likemotif which can be either Cx

4-5Cx22-23HxH (C2H2 type) or

Cx7Cx23HxC (C2HC type) The WRKY domain can be 60

amino acids long and binds DNA [20] Slight variations ofWRKYGQK can be found in some WRKY TFs The WRKYDNA-binding domain generally binds to theW-box elementscontaining the TTGAC(CT) motif though the flankingsequence adjoining theW-box dictates the binding selectivityof the TF [20] For example in contrast to other WRKYTFs WRKY6 and WRKY11 of Arabidopsis have high affinitytowards a G base upstream of the core motif of the W-box[21]

Arabidopsis being the model plant has the most wellclassified list ofWRKYproteins (Table 1)These proteins havebeen divided into three distinct groups depending on thenumbers of WRKY domains present and the diversity inthe Zn finger motifs found in them [22] The bifurcation inthe groups occurred mainly due to the number of WRKYdomains The proteins belonging to Group I have twodistinct WRKY domains while the proteins belonging toboth Groups II and III have single domains The differencebetween the proteins of Groups II and III lies in the fact thatthe former group consists of proteins with the same Cys2-His2 Zn finger motif while those belonging to the lattergroup have different Cys2-HisCys Cys2-His2 Zn fingermotif[14] On the basis of the presence of additional conservedstructural motifs Groups II and III have been further dividedinto subgroups Group IV WRKY has been characterized bythe loss of the Zn finger motif Though these proteins werethought to be nonfunctional they were found in higher algae(Bathycoccus prasinos) and some plants like rice and Vitisvinifera Recently the VvWRKYs from V vinifera have beenreported to play crucial roles in generating cold stress toler-ance in grapevines (Table 1) Structures like nuclear localiza-tion signal (NLS) leucine zippers SerThr rich stretches Glnand Pro rich stretches kinase domains and pathogenesis-related TIR-NBS-LRR domains have also been identified inthe WRKY proteins which infers the diverse roles played bythese proteins in multifarious signaling cascades [14]

4 WRKY Proteins in Stress

Under normal cellular conditions theWRKY genes regulateimportant functions related to the developmental processesin plants The expression of the Dactylis glomerata WRKYgene DGE1 is essential for proper somatic embryogen-esis [23] Strong expression of ScWRKY1 is induced inthe fertilized ovules in potato at the late torpedo stage ofembryogenesis [24] Transparent Testa Glabra 2 (TTG2) isalso named as WRKY44 and is involved in the regulation ofdevelopment of trichomes and root hairs [25] Starch produc-tion in endosperm is governed by aWRKYprotein SUSIBA2High expression ofMiniseed3 gene encoding AtWRKY10 hasbeen reported in pollens globular embryos and developingendosperms [25]

The WRKY proteins play prominent roles in the reg-ulation of transcriptional reprogramming associated withplant stress responses (Table 2) Such WRKY-mediated tran-scriptional response can be against both biotic and abioticfactors [14]TheWRKYproteins function via protein-proteininteractions and even cross regulation and autoregulation


Table1Major

families

ofWRK

Yproteins

with

associated

characteris

tics

Genefam

ilyname

Genefam

ilysubclass

Proteinassociated

Proteintype

References

Group

Imdash

AtWRK

Y1A

tWRK

Y2A

tWRK

Y1A

tWRK

Y2A

tWRK

Y3A

tWRK

Y4A

tWRK

Y10

AtWRK

Y19AtWRK

Y20AtWRK

Y25AtWRK

Y26AtWRK

Y32AtWRK

Y33

AtWRK

Y34AtWRK

Y44AtWRK

Y45AtWRK

Y58AtWRK

Y73OsW

RKY2

4OSW

RKY7

0OsW

RKY7

8OsW

RKY3

0OsW

RKY4

OsW

RKY6

3OsW

RKY6

1OsW

RKY8

1

Thep

roteinsc

ontain

two

WRK

Ydo

mains

Group

II(Arabidopsis)

IIaAtWRK

Y18AtWRK

Y40AtWRK

Y60

Sing

leWRK

Ydo

mainwith

thes

ameC

ys2-His2

Znfin

germ

otif

IIb

AtWRK

Y6A

tWRK

Y9A

tWRK

Y31AtWRK

Y36AtWRK

Y42AtWRK

Y47

AtWRK

Y61AtWRK

Y72

IIcAtWRK

Y8A

tWRK

Y12AtWRK

Y13AtWRK

Y23AtWRK

Y24AtWRK

Y28

AtWRK

Y43AtWRK

Y48AtWRK

Y49AtWRK

Y50AtWRK

Y51AtWRK

Y56

AtWRK

Y57AtWRK

Y59AtWRK

Y68AtWRK

Y71AtWRK

Y75

IIdAtWRK

Y7A

tWRK

Y11AtWRK

Y15AtWRK

Y17AtWRK

Y21AtWRK

Y39

AtWRK

Y74

[131420ndash

22117118]

IIeAtWRK

Y14AtWRK

Y16AtWRK

Y22AtWRK

Y27AtWRK

Y29AtWRK

Y35

AtWRK

Y65AtWRK

Y69

IIIa

AtWRK

Y38AtWRK

Y62AtWRK

Y63AtWRK

Y64AtWRK

Y66AtWRK

Y67

Group

II(rice)

mdashOsW

RKY5

1OsW

RKY4

2OsW

RKY2

5OsW

RKY4

4OsW

RKY6

8OsW

RKY6

OsW

RKY3

7OsW

RKY6

6OsW

RKY2

OsW

RKY13

Group

III

(Arabidopsis)

IIIb

AtWRK

Y30AtWRK

Y41AtWRK

Y46AtWRK

Y53AtWRK

Y54AtWRK

Y55

AtWRK

Y70

Sing

leWRK

Ydo

mainwith

different

Cys2-H

isCy

sCy

s2-H

is2Zn

fingerm

otif

Group

III(ric

e)mdash

OsW

RKY2

2OsW

RKY2

0OsW

RKY6

9OsW

RKY7

4OsW

RKY15OsW

RKY19

OsW

RKY4

5OsW

RKY7

5

Group

IVIVa

OsW

RKY3

3OsW

RKY3

8Presence

ofpartialZ

nfin

germ

otif

IVb

VvWRK

Y02Vv

WRK

Y29OsW

RKY5

6OsW

RKY5

8OsW

RKY5

2Lo

ssof

Znfin

germ

otif


Arabidopsis

thaliana

ldquoOsrdquoto

Oryza

sativaandldquoV

vrdquoto

Vitis

vinifer

a


Table2Ro

leof

WRK

Yproteins

inbo

thabiotic

andbioticstr

esses

Stresstype

Gene

Indu

ciblefactors

Functio

nin

stress

References

Abiotic

stress

AtWRK

Y2NaC

lmannitol

Negatively

regu

latesA

BAsig

nalin

g[74]

AtWRK

Y18

ABA

ABA

signalin

gandsalttolerance

[119]

AtWRK

Y26

Heat

Heattolerance

[34]

AtWRK

Y39

Heat

Heattolerance

[96]

AtWRK

Y40

ABA

ABA

signalin

g[119]

OsW

RKY0

8Droug

htsalinityA

BAand

oxidative

stress

Tolerancetow

ards

oxidatives

tress

[120]

OsW

RKY11

Heatdrou

ght

Xerothermicstr

esstolerance

[121]

OsW

RKY8

9Salin

ityA

BAand

UV-B


[122]

OsW

RKY4

5Salt

drou

ght

Saltanddrou

ghttolerance

[123]

OsW

RKY7

2Salt

drou

ght

Saltanddrou

ghttolerance

[124]

GmWRK

Y21

Salt

coldand

drou

ght

Coldtolerance

[72]

GmWRK

Y54

Salt

drou

ght

Saltanddrou

ghttolerance

[72]

Bioticstr

ess

AtWRK

Y38

Targetof

NPR

1duringSyste

micAc

quire

dRe

sistance(SA

R)IncreasesS

alicylicAc

id-(SA

-)mediated

respon

se[125]

AtWRK

Y53

Targetof

NPR

1duringSA

RIncreasesS

A-mediatedrespon

se[125]

AtWRK

Y66

Targetof

NPR

1duringSA

RIncreasesS

A-mediatedrespon

se[125]

AtWRK

Y70

Targetof

NPR

1duringSA

RNod

eofcon

vergence

forS

A-mediated

andjasm


defences

ignalin

g[126]

OsW

RKY3

1Magna

porthe

oryzae

Increasedresistance

[127]

OsW

RKY4

5Moryzae

Increasedresistance

[128]

OsW

RKY7

7Pseudomonas

syrin

gae

Positively

regu

latesp

lant

basalresistance

[129]

HvW

RKY10

EffectorT

riggeredIm

mun

ity(ETI)

ETIa

ctivator

[130]


Arabidopsis

thaliana

ldquoOsrdquoto

Oryza

sativaldquoG

mrdquotoGlycinem

axand

ldquoHvrdquo

toHordeum

vulga

re













Receptor

MAPKKK

MAPKK

MPK3

OsWRKY30

OsWRKY30

SP

SPP

W-box

Plasma membrane

Cytoplasm

Nucleus
















Oxidative Cold

Drought Light

Sugar starvation

Pi starvation

Salinity

OsWRKY11 AtWRKY34

AtWRKY25

AtWRKY6

AtWRKY28

AtWRKY26AtWRKY33

AtWRKY8

AtWRKY48

AtWRKY30

AtWRKY57

TcWRKY53

GmWRKY54

Heat

PtrWRKY2

TaWRKY10

AtWRKY75

VvWRKY55

BcWRKY46GmWRKY21

AtWRKY45

HvWRKY46

AtWRKY40

Radiation

OsWRKY89

Abiotic stress

























9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


Table1Major

families

ofWRK

Yproteins

with

associated

characteris

tics

Genefam

ilyname

Genefam

ilysubclass

Proteinassociated

Proteintype

References

Group

Imdash

AtWRK

Y1A

tWRK

Y2A

tWRK

Y1A

tWRK

Y2A

tWRK

Y3A

tWRK

Y4A

tWRK

Y10

AtWRK

Y19AtWRK

Y20AtWRK

Y25AtWRK

Y26AtWRK

Y32AtWRK

Y33

AtWRK

Y34AtWRK

Y44AtWRK

Y45AtWRK

Y58AtWRK

Y73OsW

RKY2

4OSW

RKY7

0OsW

RKY7

8OsW

RKY3

0OsW

RKY4

OsW

RKY6

3OsW

RKY6

1OsW

RKY8

1

Thep

roteinsc

ontain

two

WRK

Ydo

mains

Group

II(Arabidopsis)

IIaAtWRK

Y18AtWRK

Y40AtWRK

Y60

Sing

leWRK

Ydo

mainwith

thes

ameC

ys2-His2

Znfin

germ

otif

IIb

AtWRK

Y6A

tWRK

Y9A

tWRK

Y31AtWRK

Y36AtWRK

Y42AtWRK

Y47

AtWRK

Y61AtWRK

Y72

IIcAtWRK

Y8A

tWRK

Y12AtWRK

Y13AtWRK

Y23AtWRK

Y24AtWRK

Y28

AtWRK

Y43AtWRK

Y48AtWRK

Y49AtWRK

Y50AtWRK

Y51AtWRK

Y56

AtWRK

Y57AtWRK

Y59AtWRK

Y68AtWRK

Y71AtWRK

Y75

IIdAtWRK

Y7A

tWRK

Y11AtWRK

Y15AtWRK

Y17AtWRK

Y21AtWRK

Y39

AtWRK

Y74

[131420ndash

22117118]

IIeAtWRK

Y14AtWRK

Y16AtWRK

Y22AtWRK

Y27AtWRK

Y29AtWRK

Y35

AtWRK

Y65AtWRK

Y69

IIIa

AtWRK

Y38AtWRK

Y62AtWRK

Y63AtWRK

Y64AtWRK

Y66AtWRK

Y67

Group

II(rice)

mdashOsW

RKY5

1OsW

RKY4

2OsW

RKY2

5OsW

RKY4

4OsW

RKY6

8OsW

RKY6

OsW

RKY3

7OsW

RKY6

6OsW

RKY2

OsW

RKY13

Group

III

(Arabidopsis)

IIIb

AtWRK

Y30AtWRK

Y41AtWRK

Y46AtWRK

Y53AtWRK

Y54AtWRK

Y55

AtWRK

Y70

Sing

leWRK

Ydo

mainwith

different

Cys2-H

isCy

sCy

s2-H

is2Zn

fingerm

otif

Group

III(ric

e)mdash

OsW

RKY2

2OsW

RKY2

0OsW

RKY6

9OsW

RKY7

4OsW

RKY15OsW

RKY19

OsW

RKY4

5OsW

RKY7

5

Group

IVIVa

OsW

RKY3

3OsW

RKY3

8Presence

ofpartialZ

nfin

germ

otif

IVb

VvWRK

Y02Vv

WRK

Y29OsW

RKY5

6OsW

RKY5

8OsW

RKY5

2Lo

ssof

Znfin

germ

otif


Arabidopsis

thaliana

ldquoOsrdquoto

Oryza

sativaandldquoV

vrdquoto

Vitis

vinifer

a


Table2Ro

leof

WRK

Yproteins

inbo

thabiotic

andbioticstr

esses

Stresstype

Gene

Indu

ciblefactors

Functio

nin

stress

References

Abiotic

stress

AtWRK

Y2NaC

lmannitol

Negatively

regu

latesA

BAsig

nalin

g[74]

AtWRK

Y18

ABA

ABA

signalin

gandsalttolerance

[119]

AtWRK

Y26

Heat

Heattolerance

[34]

AtWRK

Y39

Heat

Heattolerance

[96]

AtWRK

Y40

ABA

ABA

signalin

g[119]

OsW

RKY0

8Droug

htsalinityA

BAand

oxidative

stress

Tolerancetow

ards

oxidatives

tress

[120]

OsW

RKY11

Heatdrou

ght

Xerothermicstr

esstolerance

[121]

OsW

RKY8

9Salin

ityA

BAand

UV-B


[122]

OsW

RKY4

5Salt

drou

ght

Saltanddrou

ghttolerance

[123]

OsW

RKY7

2Salt

drou

ght

Saltanddrou

ghttolerance

[124]

GmWRK

Y21

Salt

coldand

drou

ght

Coldtolerance

[72]

GmWRK

Y54

Salt

drou

ght

Saltanddrou

ghttolerance

[72]

Bioticstr

ess

AtWRK

Y38

Targetof

NPR

1duringSyste

micAc

quire

dRe

sistance(SA

R)IncreasesS

alicylicAc

id-(SA

-)mediated

respon

se[125]

AtWRK

Y53

Targetof

NPR

1duringSA

RIncreasesS

A-mediatedrespon

se[125]

AtWRK

Y66

Targetof

NPR

1duringSA

RIncreasesS

A-mediatedrespon

se[125]

AtWRK

Y70

Targetof

NPR

1duringSA

RNod

eofcon

vergence

forS

A-mediated

andjasm


defences

ignalin

g[126]

OsW

RKY3

1Magna

porthe

oryzae

Increasedresistance

[127]

OsW

RKY4

5Moryzae

Increasedresistance

[128]

OsW

RKY7

7Pseudomonas

syrin

gae

Positively

regu

latesp

lant

basalresistance

[129]

HvW

RKY10

EffectorT

riggeredIm

mun

ity(ETI)

ETIa

ctivator

[130]


Arabidopsis

thaliana

ldquoOsrdquoto

Oryza

sativaldquoG

mrdquotoGlycinem

axand

ldquoHvrdquo

toHordeum

vulga

re













Receptor

MAPKKK

MAPKK

MPK3

OsWRKY30

OsWRKY30

SP

SPP

W-box

Plasma membrane

Cytoplasm

Nucleus
















Oxidative Cold

Drought Light

Sugar starvation

Pi starvation

Salinity

OsWRKY11 AtWRKY34

AtWRKY25

AtWRKY6

AtWRKY28

AtWRKY26AtWRKY33

AtWRKY8

AtWRKY48

AtWRKY30

AtWRKY57

TcWRKY53

GmWRKY54

Heat

PtrWRKY2

TaWRKY10

AtWRKY75

VvWRKY55

BcWRKY46GmWRKY21

AtWRKY45

HvWRKY46

AtWRKY40

Radiation

OsWRKY89

Abiotic stress

























9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


Table2Ro

leof

WRK

Yproteins

inbo

thabiotic

andbioticstr

esses

Stresstype

Gene

Indu

ciblefactors

Functio

nin

stress

References

Abiotic

stress

AtWRK

Y2NaC

lmannitol

Negatively

regu

latesA

BAsig

nalin

g[74]

AtWRK

Y18

ABA

ABA

signalin

gandsalttolerance

[119]

AtWRK

Y26

Heat

Heattolerance

[34]

AtWRK

Y39

Heat

Heattolerance

[96]

AtWRK

Y40

ABA

ABA

signalin

g[119]

OsW

RKY0

8Droug

htsalinityA

BAand

oxidative

stress

Tolerancetow

ards

oxidatives

tress

[120]

OsW

RKY11

Heatdrou

ght

Xerothermicstr

esstolerance

[121]

OsW

RKY8

9Salin

ityA

BAand

UV-B


[122]

OsW

RKY4

5Salt

drou

ght

Saltanddrou

ghttolerance

[123]

OsW

RKY7

2Salt

drou

ght

Saltanddrou

ghttolerance

[124]

GmWRK

Y21

Salt

coldand

drou

ght

Coldtolerance

[72]

GmWRK

Y54

Salt

drou

ght

Saltanddrou

ghttolerance

[72]

Bioticstr

ess

AtWRK

Y38

Targetof

NPR

1duringSyste

micAc

quire

dRe

sistance(SA

R)IncreasesS

alicylicAc

id-(SA

-)mediated

respon

se[125]

AtWRK

Y53

Targetof

NPR

1duringSA

RIncreasesS

A-mediatedrespon

se[125]

AtWRK

Y66

Targetof

NPR

1duringSA

RIncreasesS

A-mediatedrespon

se[125]

AtWRK

Y70

Targetof

NPR

1duringSA

RNod

eofcon

vergence

forS

A-mediated

andjasm


defences

ignalin

g[126]

OsW

RKY3

1Magna

porthe

oryzae

Increasedresistance

[127]

OsW

RKY4

5Moryzae

Increasedresistance

[128]

OsW

RKY7

7Pseudomonas

syrin

gae

Positively

regu

latesp

lant

basalresistance

[129]

HvW

RKY10

EffectorT

riggeredIm

mun

ity(ETI)

ETIa

ctivator

[130]


Arabidopsis

thaliana

ldquoOsrdquoto

Oryza

sativaldquoG

mrdquotoGlycinem

axand

ldquoHvrdquo

toHordeum

vulga

re













Receptor

MAPKKK

MAPKK

MPK3

OsWRKY30

OsWRKY30

SP

SPP

W-box

Plasma membrane

Cytoplasm

Nucleus
















Oxidative Cold

Drought Light

Sugar starvation

Pi starvation

Salinity

OsWRKY11 AtWRKY34

AtWRKY25

AtWRKY6

AtWRKY28

AtWRKY26AtWRKY33

AtWRKY8

AtWRKY48

AtWRKY30

AtWRKY57

TcWRKY53

GmWRKY54

Heat

PtrWRKY2

TaWRKY10

AtWRKY75

VvWRKY55

BcWRKY46GmWRKY21

AtWRKY45

HvWRKY46

AtWRKY40

Radiation

OsWRKY89

Abiotic stress

























9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology













Receptor

MAPKKK

MAPKK

MPK3

OsWRKY30

OsWRKY30

SP

SPP

W-box

Plasma membrane

Cytoplasm

Nucleus
















Oxidative Cold

Drought Light

Sugar starvation

Pi starvation

Salinity

OsWRKY11 AtWRKY34

AtWRKY25

AtWRKY6

AtWRKY28

AtWRKY26AtWRKY33

AtWRKY8

AtWRKY48

AtWRKY30

AtWRKY57

TcWRKY53

GmWRKY54

Heat

PtrWRKY2

TaWRKY10

AtWRKY75

VvWRKY55

BcWRKY46GmWRKY21

AtWRKY45

HvWRKY46

AtWRKY40

Radiation

OsWRKY89

Abiotic stress

























9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology



Receptor

MAPKKK

MAPKK

MPK3

OsWRKY30

OsWRKY30

SP

SPP

W-box

Plasma membrane

Cytoplasm

Nucleus
















Oxidative Cold

Drought Light

Sugar starvation

Pi starvation

Salinity

OsWRKY11 AtWRKY34

AtWRKY25

AtWRKY6

AtWRKY28

AtWRKY26AtWRKY33

AtWRKY8

AtWRKY48

AtWRKY30

AtWRKY57

TcWRKY53

GmWRKY54

Heat

PtrWRKY2

TaWRKY10

AtWRKY75

VvWRKY55

BcWRKY46GmWRKY21

AtWRKY45

HvWRKY46

AtWRKY40

Radiation

OsWRKY89

Abiotic stress

























9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology










Oxidative Cold

Drought Light

Sugar starvation

Pi starvation

Salinity

OsWRKY11 AtWRKY34

AtWRKY25

AtWRKY6

AtWRKY28

AtWRKY26AtWRKY33

AtWRKY8

AtWRKY48

AtWRKY30

AtWRKY57

TcWRKY53

GmWRKY54

Heat

PtrWRKY2

TaWRKY10

AtWRKY75

VvWRKY55

BcWRKY46GmWRKY21

AtWRKY45

HvWRKY46

AtWRKY40

Radiation

OsWRKY89

Abiotic stress

























9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


Oxidative Cold

Drought Light

Sugar starvation

Pi starvation

Salinity

OsWRKY11 AtWRKY34

AtWRKY25

AtWRKY6

AtWRKY28

AtWRKY26AtWRKY33

AtWRKY8

AtWRKY48

AtWRKY30

AtWRKY57

TcWRKY53

GmWRKY54

Heat

PtrWRKY2

TaWRKY10

AtWRKY75

VvWRKY55

BcWRKY46GmWRKY21

AtWRKY45

HvWRKY46

AtWRKY40

Radiation

OsWRKY89

Abiotic stress

























9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology





















9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology
















9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology









9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




9 Conclusion





responses


responses

SA JA

ABA

SA JA

ABASA JA

ABA






Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


Acknowledgments


References

















































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




















































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology



















































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




















































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




















Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology








Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

Documents

Review Article WRKY Proteins: Signaling and Regulation of ...Review Article WRKY Proteins: Signaling and Regulation of Expression during Abiotic Stress Responses AdityaBanerjeeandAryadeepRoychoudhury