Transgenic Approach for Abiotic Stress Tolerance

Characteristics features of plant stress protein

No. Stress Protein Induction agent Characteristics features

1 HSP (heat shock protein)

Mostly by high temperature stress, also by water stress, salt stress, low temperature stress, in some cases also by abscisic acid

Classified aslow molecular weight HSPs and high molecular weight HSPs, highly conserved amino acid sequence, nucleotide sequence of the corresponding genes is also conserved, stress-inducible of hs genes governed by HSEs (heat shock elements), selected HSPs are shown to act as chaperons

2 Osmotic stress proteins such as WSPs (water stress proteins) and SSPs (salt stress proteins)

Mostly by low water availability and salt stress, also induced by ABA

Varied molecular weights and cellular locations, these proteins are mostly the enzymes involved in diverse functions such as production of different osmolytes, protein degradation, signal transduction events, gene regulation and transport. Roles of some WSPs is not well defined (i.e. such as for dehydrins, late embryogenesis, abundant proteins)

Characteristics features of plant stress protein

No. Stress Protein Induction agent Characteristics features

3 ANPs (anaerobic proteins)

Mostly by anaerobic stress (caused by flooding or submergence stress)

Discovered initially in maize and later shown tin o be universally present, most of the ANPs have been shown to be the enzymes of the fermentative or the glycolytic pathway, most genes encoding ANPs contain . AREs (anaerobic response elements) in their promoters

4 Cold stress proteins such as COR (cold-regulated proteins)

Mostly by low temperature stress, also by osmotic, oxidative stress and ABA

Conserved proteins of varied sizes and functions, most COR genes contain specific nucleotide sequence that stimulate transcription in response to low temperature

Stress Induced gene expression

1.Genes encoding proteins with known enzymatic or structural functions

2.Protein with as yet unknown functions3.Regulatory protein

Single action gene

Osmoprotectant genes: Proline, Gly/Bet, Sugar polyolsDetoxifying genes: SOD, PXLate embryogenesis abundant genes: LEATransporter genes: Aquapurin, Ion transporterMultifunctional genes for lipid biosynthesis:GPAT

(glycerol-3-phosphate acyltransferase), FAD7 (Fatty acid desaturase)

Heat shock genes: HS

Regulatory Genes

Transcription factors genes CBF/DREB, ABF, HSF, bZIP, MYC/MYB

Signal transduction genesa. Osmocensors (AtHK-1)b. Phospholipid cleaving enzymes (PLD)c. Second messengers (Ptd-OH, ROS)d. MAP kinases, Ca+ censor (SOS-3)e. Calcium –dependent protein kinases (CDPKs)

Abiotic stress tolerance1.Increase cellular level of osmotically-active

solute (proline, glycinebetaine, mannitol, trehalose, fructans)

2.Increase levels of osmolytes3.It is mediated by a number of biochemical

reactions /physiological processes (a multi genic trait)

4.It can be augmented by pyramiding different stress-responsive genes

Osmolyte and Compatible Solutes

Gene Protein Source Cellular role(s)

gpat Glycerol 3-phosphate acyltransferase

Cucurbita maxima, Arabidopsis thaliana

Fatty acid unsaturation

mtlD Mannitol 1-phosphate dehydrogenase

Eschericia coli Manitol biosynthesis

sod Superoxide dismutase

Nicotiana plumbaginifolia

Superoxide dismutase

Bet-B Betaine aldehyde dehydrogenase

Eschericia coli Glycinebetaine dismutase

Gene Protein Source Cellular role(s)

Bet-A Choline dehydrogenase

Eschericia coli Glycinebetaine dismutase

p5cs Pyroline 5-carboxylase synthase

V. aconitifolia Proline biosynthesis

Sac-B Levan sucrase Baccilus subtilis Fructan biosynthesis

Hva-1 LEA protein Hordeum vulgare

-

Tps-1 Trehalose 6-phosphate synthase

Arabidopsis thaliana

Trehalose biosynthesis

Osmolyte and Compatible Solutes

Gene Protein Source Cellular role(s)

Cod-A/Cod-1/Cox Choline oxidase Arthrobacter globiformis

Glycinebetaine biosynthesis

afp Antifreeze protein (AFP)

Synthetic Inhibit ice growth and recrystallization

Imt-1 Myo-inositol-o-methyl transferase

Messembryanthemum crystallinum

D-ononitol biosynthesis

BADH Betaine dehydrogenase

Spinach Glycinebetaine byosynthesis

Osmolyte and Compatible Solutes

Gene Protein Source Cellular role(s)

Ect-A, Ect-B, Ect-C

L-2,4-diaminobutyric acetyltransferaseL-2,4-diaminobutyric acid trans-aminaseL-ectoine synthase

Halomonas elongata

Ectoyne

Ots-A, Ots-B Trehalose-6-P synthaseTrehalose-6-P phosphatase

Eschericia coli Trehalose

Osmolyte and Compatible Solutes

Gene Protein Source Cellular role(s)

Pro-DH Proline dehydrogenase

Arabidopsis thaliana

Proline

HAL-3 FMN-binding protein

Saccharomyces cerevisae

Na+/K+ homeostasis

Osmolyte and Compatible Solutes

Gene Protein Source Cellular role(s)

AtNHX-1 Vacuolar Na+/H+ antiporter

Arabidopsis thaliana

Na+ vacuolar sequestration

AtSOS-1 Plasma membrane Na+/H+ antiporter

Arabidopsis thaliana

Na+ extrusion

AVP-1 Vacuolar H+-pyrophosphatase

Arabidopsis thaliana

Vacuolar acidification

HAL-1 K+/Na+ transport regulation

Saccharomyces cerevisiae

K+/Na+ homeostasis

Ion Transporters and Ion Homeostasis

Gene Protein Source Cellular role(s)

MnSOD Superoxide dismutase

Saccharomyces cerevisiae

Reduction of O2 content

Gly-1 Glyoxylase Brassica juncea S-D-lactoylglutathione

TPX-2 Peroxidase Nicotiana tabacum

Change cell properties

GST

GPX

Glutathione S-transferaseGlutathione peroxidase

Nicotiana tabacumNicotiana tabacum

ROS scavenging

Redox Proteins

Gene Protein Source Cellular role(s)

DREB-1A Transcription factor

Arabidopsis thaliana

Improved gene expression

Cnb-1 Calcineurin Saccharomyces cerevisiae

Improved Ca++ signaling

OsCDPK-7 Protein kinase Oryza sativa Improved gene expression

Transcription and signal transduction factors

Gene Protein Source Cellular role(s)

DnaK Heat shock protein

A. halophytica

Protein stabilization

Apo-Inv Apoplastic yeast-derived invertase

Saccharomyces cerevisiae

Sucrose synthesis

Mischelineous

Perspective in Abiotic Stress Tolerance

1. Abiotic stress elicit multigenic responses within the plant cells. The tolerance to different abiotic stress is contributed by a range of different biochemical/physiological mechanism

2. Only a limited number of plant genes with a definite function have been identified, cloned and characterized

3. Changing levels of transcription factors can alter the levels of several genes at the same time

4. The transgenics raised far for enhancing tolerance to abiotic stress have been achieved through employing strong constitutive promoters, for driving expression of the transgenes. Promoters which are induced by different abiotic stress including high temperature stress, anaerobic stress, salt stress and water stress have poor strength of expression when compared to constitutively expression promoter