Drought Tolerance of Crops: Progress and Challenges

Dr. Viswanathan Chinnusamy

Principal Scientist

Division of Plant Physiology

IARI, New Delhi 110012

Email: viswanathan@iari.res.in

OUTLINE

• Introduction to drought stress

• Target Environment

• Mechanisms of drought tolerance

• Physiological and molecular genetic

basis of drought tolerance

• Yield stability under drought

• Challenges:

o MIADE

o Realistic, accurate and high

throughput Phenotyping

o Molecular genetics of crop plants

•Water - deficit, hypoxia, anoxia

•Temperature- Low, High

•Nutrients – deficiency, toxicity

•Light - low, high

•pH – acidity, alkalinity

ABIOTIC STRESSES

Scarcity or excess of essential

environmental factors

•Ionic toxicity - salinity,

alkalinity, heavy metals

•Air pollution

•UV-B radiation

Excess of non-essential

environmental factors

Quantity of factor G

row

th

Quantity of factor

Gro

wth

Drought

Soil moisture

PWP FC Water

logging

Cro

p Y

ield

Meteorological drought: Deficit in precipitation over a long term average

Agricultural drought: Soil moisture deficit that leads to reduction in growth,

development and yield of crops

Drought = moisture deficit stress

water stress

Target environment

Water Availability

Yie

ld

50 100 25

Water scarcity

Wate

r avail

ab

ilit

y

Crop growth stage

FC

PWP

Terminal Intermittent

Drought Stress Tolerance is No More a Myth

• It is very common to state that drought tolerance is a “very complex

trait” and it is not tractable for genetic improvement.

• It is often believed that “drought tolerance is a nebulous term that

becomes more nebulous the more closely we look at it, much as

a newspaper photograph does when viewed through a

magnifying glass” (Passioura 1996).

• This opinion emerged rather due to a global view of yield response of

plants under illdefined experimental conditions or agricultural

situations. Hence the results are confusing and non-reproducible.

• Omics of plant stress response revealed massive change in

epigenome, transcriptome, proteome and metabolome in response to

drought that further strengthened the opinion that drought tolerance is

a very complex trait.

• "Clearly, recently we have seen some very promising advances in terms of

drought tolerances in crop plants," says Nguyen. "Now it's a question of how

to optimize the system."

• Tester is also optimistic: Ultimately, "I think there will be a palette of genes from

which breeders and crop scientists will select for putting together the

drought tolerance for a particular region.” (Pennisi E. 2008)

Complex traits are amenable for easy modification

• GA regulated genes are more than 1100 in Arabidopsis seedlings.

• Yield improvement in green revolution is brought about by single gene mutation that

resulted in gibberellin (GA) deficiency in rice (semi-dwarf1/sd1) and GA insensitivity

in wheat (Reduced height/Rht).

The mechanisms causing minimum loss of yield in a water

deficit environment relative to the maximum yield in a water

constraint free management of the crop.

Drought Tolerance Drought Resistance

Drought Tolerance

Dehydration

Avoidance

Dehydration

tolerance

Drought Tolerance

Constitutive

mechanisms

Acquired

mechanisms

where: WU= water transpired by the crop

WUE = water use efficiency (=biomass/unit water transpired)

HI = harvest index (economic yield/total biomass)

Passioura (1977)

GY = WU x WUE x HI

Yield Stability

Phenotypic &

developmental

plasticity

Water Mining (WU) Minimizing

water loss

WUE &

EUW

Cellular tolerance

Drought Tolerance

Root traits-

Morphological &

anatomical changes

Aquaporins

OA

Transpiration -Stomata

LAI (Leaf area, no.

Leaf rolling & drying)

leaf reflectance

characters (wax load

and pubescence, leaf

angle, leaf rolling)

Metabolic homeostasis

Xanthopyll cycle

Photorespiration

Maintenance respiration

Osmoprotection

Cell membrane stability

Oxidative Stress Mgmt.

Stress proteins

Activity &

Efficiency of

rubisco at low Ci

Phenology

Flowering

Development

Dehydration Avoidance Dehydration tolerance

Recovery, growth, yield + ABA

-CK, Ethylene

+ ABA

+CK, Auxin, GA,

Traits & Genes:

Water Mining

Root-ABA1, a major constitutive

QTL, affects maize root architecture

and leaf ABA concentration

Giuliani et al. 2005. J Exp Bot. 56: 3061–3070

Root-yield-1.06, a major constitutive QTL

for root and agronomic traits in maize

across water regimes

Landi et al. 2010. J Exp Bot. 61: 3553–3562

QTLs for Root System Architecture

PW

RK

Y6::

CK

Xo

x

Root-specific manipulation of single gene expression can increase root traits

CL, Culm length

PL, panicle length

NP, number of panicles per hill

NSP, number of spikelets per panicle

TNS, total number of spikelets

FR, filling rate

NFG, number of filled grains

TGW, total grain weight

1,000GW, 1,000 grain weight.

NT RCc:OSNAC10

Plant Physiology, May 2010, Vol. 153, pp. 185–197,

cDNA microarray of drought stress response in rice SNAC1 with 5.6 fold

enhanced expression was isolated from the upland rice cultivar IRAT109.

WT 35S::SNAC1

Hu et al. PNAS USA 103: 12987–12992

Application of omics technologies has contributed to the development

of stress-tolerant crops in the field

The hrd-D mutant showed more

secondary roots in Arabidopsis

Genes for root traits

+ ABA + Auxin - CK - Ethylene

QTLs for osmotic adjustment in rice

Traits & Genes: Osmotic Adjustment

High OA Low OA

Garg et al. 2002. 99:15898-15903

Traits & Genes: WUE

Crop No. of QTLs References

Wheat 10 QTLs affecting per plant WUE (Total dry

matter/ amount of water used by per plant)

Zhang et al., 2002

Rice 7 QTLs located in 5 chomosomal regions. Xu et al., 2009

ERECTA, a putative leucine -rich repeat receptor-like kinase (LRR-RLK), known for its

effects on inflorescence development, is a major contributor to a 13C QTL on chr2.

ABA pathway engineering:

Minimization of water loss &

Enhancement of cellular tolerance

ab

a2

W

T

/aba3

90% ~30% RH,

10 min WT aao3

Isomerase/A

BA4

ABA2

BG1

NCED3-ox WT

vp14

WT

Traits & Genes: Transpiration control & Cellular tolerance

• ABA: Water mining – Regulate primary root growth; Minimization of transpiration –

Stomatal Control; Osmotic adjustment – regulates gene expression; Cellular tolerance

Negative regulators and effectors are shown in red for clarity. Colors in boxes

represent relative expression level of a gene before and after ABA treatment

(+ABA).

Plant Cell 16:596-615 (2004)

ABA Signal Transduction

The DH12075 (a) and YPT2-RD29A-

antiAtFTP (b) plants were subjected to a

4-day drought treatment starting on day 8

after flowering. The pictures were taken

on day 8 of re-watering after the drought

stress

Drought tolerance of rd29A:anti-AtFTB canola during flowering

In (a) the solid bars represent

seed yields for the two-

irrigation condition, and the

dotted bars represent seed

yields for the one irrigation

condition. Irrigation was

conducted during the

flowering period.

Seed yields of WT and transgenic canola in 2003 (a) and 2004 (b) confined field trials

Wang et al. 2005. Plant J. 43: 413–424

Oh et at. 2005. Arabidopsis CBF3/DREB1A and ABF3 in transgenic rice

increased tolerance to abiotic stress without stunting growth. Plant

Physiology 138:341-351

ABA confers dessication tolerance – from moss to higher plants

Red Arrow indicates re-watering

2009 Science’s TOP 10

Identification of the ABA receptors and its mechanism of action

Science Breakthrough 2009

“These results are a boon for plant biology—and possibly beyond. The PP2C and the

ABA receptors both belong to highly conserved families of proteins whose roles in other

organisms may become clearer now that their function in plants has been nailed down”

ABF3

P

Hubbard K E et al. (2010) Genes Dev. 24:1695-1708

Traits & Genes: Transpiration control & Cellular tolerance

Overexpression of ABA Receptor enhances drought tolerance

Wheat seedlings grown in vermiculite

and severely desiccated under drought.

The seedling on the right received 0.1

µmol of ABA in the irrigation water

before the onset of stress. Control

seedlings received normal irrigation

water before on the left.

Vaccination ?

• Identification of new agonist chemicals

• Engineered receptors that can be

activated by the “off-the-shelf”

agrochemicals

Yield stability under field drought stress conditions

Molecular basis of spikelet fertility under drought stress needs to be studied

Spikelet Fertility

Reproductive stage stress tolerance

Regulated Expression of an Isopentenyltransferase Gene (PSARK::IPT) in

Peanut Significantly Improves Yield Under Field Drought Conditions

Qin et al. 2011. Plant Cell Physiol 52: 1904-1914

NT PSARK::IPT

Expression of IPT in

senescence associated

promoter in leaves increases

drought tolerance

Plant nuclear factor Y (NF-Y) B subunits improved corn yields under drought

Nelson et al. 2007. PNAS USA 104: 16450-16455

Castiglioni et al. 2008. Plant Physiology 147: 446–455

Bacterial RNA Chaperones Confer Improved Grain Yield in Maize under Water-

Limited Conditions

Vandana x Way Rarem qtl12.1

This QTL accounted for an increase in grain yield, harvest index, and biomass yield under

stress, and it was detected over seasons under field conditions. The QTL accounted for

51% of the genetic variance in yield under drought

Bernier J, Kumar A, Ramaiah V, Spaner D, Atlin G (2007). A large-effect QTL for grain

yield under reproductive-stage drought stress in upland rice. Crop Sci. 47:505-516

A QTL on chromosome 1 that accounts for 32% of the variation in yield under drought

stress in rainfed lowland rice.

Kumar R, Venuprasad R, Atlin GN (2007). Genetic analysis of rainfed lowland rice

drought tolerance under naturally-occurring stress in eastern India: heritability and

QTL effects. Field Crops Res.103:42-52.

QTL for Yield under drought

QTL qtl12.1 increases water uptake in upland rice:

Bernier et al. 2009. Field Crops Research 110: 139-146

qtl12.1 has a large and consistent effect on grain yield under upland drought stress

conditions, in a wide range of environments (21 field trials)

Bernier et al. 2009. Euphytica 166:207–217

Trends in Plant Science,

June 2011, Vol. 16, No. 6

Yang et al. 2010. Mol Plant 3: 469–490

Yang et al. 2010. Mol Plant 3: 469–490

Controlled environment phenotyping: Phenomics

Large scale phenotyping under natural field – A OPEN CHALLENGE

CHALLENGE - 1

Minimum Information about a Drought Experiment (MIADE)

1. Agronomic conditions of crop culture: Soil type, pH and Ec; nutrition;

spacing between plants

2. Soil water status: soil matric potential, amount and interval of irrigation

3. The crop growth stage at which the stress was imposed

4. Duration of stress

5. Plant water status: RWC or water potential and osmotic potential

6. Phenology, Yield and yield components

7. Weather data on rainfall, temperature and VPD

CHALLENGE - 2

1. Genotypes:

• Germplasm Cores Mini-cores

• Mutants – T-DNA/Transposon tagged lines

2. Genomics:

• OMICS and Bioinformatics

3. Efficient and Easy Transformation Protocols

– Rate limiting step in gene function validation

Crop Functional Genomics

CHALLENGE - 3

Rate limiting traits/processes/genes

Mutants

Phenotyping

Gene

cloning

Germplasm

Phenotyping

Contrasting

genotypes

QTL Mapping

Association

mapping (LD)

• WGA

GENES

MAS Breeding Transgenics

Genotype with improved stress tolerance

Rate limiting traits/processes/genes

Yield

Component

Pathways

Component Traits

Genes

Yield

CHALLENGE - 4

Potential combinations of environmental

stresses that can affect crops in the field

Yet to learn of the alphabets of the stress matrix

CHALLENGE - 5

Systems biology

CHALLENGE - 6

Collaboration & Translation of research findings in to products

YIELD

OmicsCellular

networksGrowth models

Drought tolerance can be improved – Drop by drop

– Gene by Gene

– Trait by Trait

X ?

Be SPECIFIC – Target Environment, Pyramid Traits

One who solves the problem of WATER is worth two NOBEL Prizes

one for SCIENCE and one for PEACE - John F. Kennedy

viswanathan@iari.res.in

Thanks