Pavan. RPh. D Scholar

Department of Genetics and Plant BreedingUniversity of Agricultural Sciences

Bengaluru-65Email: pavan_55agri@gmail.com

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Water availability in different continents Vs population

Continents Available water (%)

Population (%)

North America 15 8

South America 26 6

Islands 5 1

Europe 8 13

Africa 11 13

Asia 36 60

Source: Kannada Prabha daily news paper

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Abiotic stress1. Drought

2. High temperature ( above threshold temperature)

3. Cold temperature Freezing stress [<0◦C to -30 ◦C] and Chilling stress [1 to 6 ◦C ]

1. Salinity

2. Flooding

3. Heavy metals (Al, Zn, Cd)

4. Wind

5. Elevated CO2

6. Ozone and UV-B 6

Source: Australian Centre for International Agricultural Research

Drought stress

Heat stress

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Abiotic Stress Tolerant Breeding SitesCRIDA,

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"Drought stress is a condition of moisture deficit sufficient to have an adverse effect on vegetation, animals, and man over a sizeable area"

Heat stress is defined as “the rise in temperature beyond a threshold level for a period of time sufficient to cause irreversible damage to plant growth and development”

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Drought stress Vs heat stress• Its difficult to delineate between drought and

heat stress

• Drought stress often occurs together with heat

stress in the field

• The regulatory system for both stresses may

have co-evolved [Barnabas et al. 2008]

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Time and intensity of stress• Depending upon time of water stress, flowering

is advanced or postponed

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18◦C 28◦C

Days to Development of Node (DDN)

Number of nodes to first flower (NTFF)

- 8

- 6

- 4

- 2

12 -

10 -

8 -

6 -

4 -

2 -

U shaped response

Vegetative phase is increased

Schematic overview of the reproductive cycle in cereals and the effect of abiotic stress on different stages of reproductive development12

Drought-induced Abscisic Acid (ABA)-dependent plant responses 13

Effect of water deficiency on Flower initiation

• Delay in flower induction and inflorescence

development leads to a delay in flowering

(Winkel et al. 1997)

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Effect of High temperature on flower initiation

• Temperatures > 30 °C during floret formation cause complete sterility in wheat

Saini & Aspinall (1982)• In wheat, the number of kernels per unit area

decreases at a rate of 4% for each degree increase in mean temperature during anthesis

Fischer (1985)• In rice, floral abnormalities induced by heat stress (i.e.

stamen hypoplasia and pistil hyperplasia), leading to spikelet sterility

Takeoka et al. (1991)15

Water deficiency on ovary and female Water deficiency on ovary and female gametophyte developmentgametophyte development

• In maize, drought stress leads to delay in female organ development, while the male inflorescence is less affected

• in the ABA concentration of the ovary when

compared with irrigated maize plants

• High ABA levels in early reproductive structures may inhibit cell division and impair floret and then seed development

Yang et al. (2001a)16

• During water deficit, the phloem-mobile dye carboxyfluorescein is fed to the stems of maize

• They found less movement to the ovary than in controls supplied with water

• This confirmed that less sugar was delivered by the phloem to the pedicel during water shortage

Makela et al. (2005)

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• The ovaries also displayed less cell wall-bound invertase activity when the plants were subjected to a water shortage

Zinselmeier et al. (1995)

• In Arabidopsis reported that, even in harshly stressed condition plants can allocate sufficient resources into the female generative organs to produce a few seeds, ensuring that the genetic line is continued

Sun, et al. (2004)

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Effect of elevated temperature on ovary and

embryo sac development

• Saini & Aspinall (1982) observed that a level of heat

stress that caused male sterility in wheat had no

damaging influence on the functions of female sexual

generation, suggesting that the female gametophyte

had greater heat stress tolerance

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Effect of water deficiency on Effect of water deficiency on pollen developmentpollen development

• Water deficit in the meiotic stage may reduce the grain

set by 35–75% in various cultivars of self-pollinated crops

• In case of wheat, drought stress results in increased

pollen sterility due to abnormalities in microsporogenesis

and microgametogenesis

Saini et al. (1984)

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The effect of drought stress (no water for 5 days) at the young microspore stage in wheat

Source: Rudy et al 2011, Plant Science 21

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Effects of heat stress on reproductive phase...?

Alter male fitness

In Datura (Buchholz and Blakeslee, 1927) where pollen tube growth rate increased linearly by a factor of 4.5 from 11 ◦C to 33 ◦C (from 1.28 mm/h to 5.86 mm/h). Pollen tube growth rate increased

In Datura (Buchholz and Blakeslee, 1927) where pollen tube growth rate increased linearly by a factor of 4.5 from 11 ◦C to 33 ◦C (from 1.28 mm/h to 5.86 mm/h). Pollen tube growth rate increased

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25Prasad et al. (1999)

Effect of drought stress on fertilization

• In maize, abortion is highly dependent on the

timing of water stress: low water availability

before pollination resulted in abortion even if

sufficient water was available at the time of

pollination

(Westgate & Boyer 1986)

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27O’Toole (1982)

28Claassen & Shaw (1970)

Effect of heat stress on fertilization

• In wheat, High-temperature stress (>30 °C) from

early meiosis to pollen maturity has a damaging

effect on the viability of pollen grains, resulting in

a failure of fertilization, and thus in a reduction in

seed set

(Saini & Aspinall,1982)

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• Increased temperature over the mid-anthesis period decreased the grain number per ear at maturity in spring wheat

Ferris et al. (1998)

• Sterility is caused by poor anther dehiscence and low pollen production, and hence low number of germinating pollen grains on the stigma

• In maize, reduction in seed set occurs at temperatures higher than 38 °C mainly because of a reduction in pollen germination ability and pollen tube elongation

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Prasad et al. 2006

Stone, 2001

Grain Filling Under Heat And Drought

• Large yield losses in cereals because of reduction in starch accumulation

• In wheat, drought (20 days at endosperm cell division) resulted in 30–40% lower endosperm cell number, and the number of small starch granules per cells was also reduced by 45%

(Nicolas et al. 1985)

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Crops: Cowpea, groundnut and Bambara groundnut

Treatment:

1. Liberal watering until maturity

2. Seven-day dry cycle from 41 to 47 DAP

3. Two dry cycles: from 41 to 47 DAP followed by resumed liberal watering and another dry cycle from 54 to 59 DAP

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Climatic conditions at Legon during study period (January-April 2000)

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Effect of water stress on pod and seed yield

35Source: Wahid et al (2007)

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Traits related to tolerance ofhigh temperature stress in rice

Plant architecture: The panicle is surrounded by many leaves

Time of flowering and anthesis

Length of anther

Size of basal pore

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Strategies adapted by all forms of life

to mitigate stress

Tolerance

Avoidance

A boring lecture

Escape

Plant responses to water deficit

Ability to complete life cycle during wet periods

Ability to maintain tissue hydration.Eg: Leaf rolling, Epicuticular Wax, Deep roots Ability to function

while dehydration 38

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The dilemma of plants

Water spenders

Water Savers

Advances To Combat

Abiotic Stress

Tolerance

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Conventional Breeding approach

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1.Germplasm evaluation and enhancement

2.Breeding for earliness

3.Breeding for root traits

Molecular Breeding approach

• Genome sequence of many crops available now

• Next generation sequencing: cheap and quick

• Approaches: 1. Identification of QTLs

• Until recently linkage mapping

• Nested association mapping

2. Introgression of QTLs: MABC

Very few examples for drought and heat tolerance

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• In this study, the genetic bases of DT and DA at reproductive stage in rice were analyzed using a 180 RIL’s of F9/F10 generation from a cross between an indica lowland and a tropical japonica upland cultivar

• 21 traits measuring fitness, yield, and the root system were investigated

• 9 traits are collected above ground level and other 12 are root traits 43

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1. Water use efficiency (WUE): Increasing the yield or biomass per unit of water availability

Unit: (g DM/Kg water used)

WUE can be increased either

by decreasing transpiration or

by increasing photosynthetic rate

By using high wax line, we can achieved 2-3 fold increase in WUE

PHYSIOLOGICAL APPROACH

2. Osmotic adjustment net increase in intercellular

solutes in response to water stress, which allows turgor maintenance at lower water potential

Target : Gene encoding rate limiting enzymes in biosynthetic pathway of various osmolytes like Proline, mannitol etc

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• Proline : Amino acid• Targeted P5C5 gene• Codes for rate limiting enzyme in Proline biosynthesis

pathway• P5C5 gene from Vigna (cowpea) overexpressed in

tobacco

• Result: P5C5 transgenics highly tolerant to stress

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The Sugar alcohols eg., mannitol

Most important sugar alcohol : Excellent combatable solute

Synthesized by 50 families of angiosperms

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No Benefit Full Benefit

Benefits of OA are stage dependent

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Locating genomic regions associated with components of drought resistance in rice Zhang, et al., 2001

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3.Epicuticular waxes

Quality Quantity

Determines water lossVery Long Chain Fatty Acid products generated in

epidermis are used for synthesis of other wax components

EW manipulation can be viable option to increase stress tolerance

Waxes increases understress

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Wax encoding genes identified Gene Site of action

CER 5 Codes for ABC transporter involved in wax transporter from inner to

outer surface of epidermis

CUT 1 90 % identical to CER-5

WAX 2 32 % identity with CER-1 and involved in cuticle membrane

development

WIN 1 Wax inducer 1 from Arabidopsis, activated several genes involved in

decarbonyalation pathway of wax production

SHINE 1 Same as WIN-1

WXP-1 Wax production 1 from Medicago trunculata,

Activates several genes involved in acyl reduction pathway of wax

production 58

Asaph et al., 2004 Plant Cell

Increased wax synthesis improved drought tolerance

Evidences

Transcriptional factors regulating wax biosynthesis

SHINE/WIN1-AP2 ERF Transcription factorsSHINE/WIN1-AP2 ERF Transcription factors

Potential candidate genesPotential candidate genes

SHINE, CERSHINE, CER

WT WXP1 transgenics

3d after drought stress

Zhang et al., 2005, Plant journal

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1. Osmoprotectants: involves the upregulation of compatible solutes (osmolytes) that function primarily to maintain cell turgor

• Compatible solutes are low molecular weight, highly soluble compounds that are usually nontoxic at high cellular concentrations

• The three major groups of compatible solutes are

Amino acids (such as proline),

Quaternary amines (such as glycine betaine (GlyBet),

polyamines, and dimethylsulfonioproprionate),

Polyol/Sugars (such as mannitol, galactinol, and trehalose

Molecular Responses

2. Late embryogenesis abundent proteins

• LEA proteins are produced in response to dehydration stress

• Functions: Protection of cytosolic structures, Ion sequestration, Protein renaturation, Transport of nuclear targeted proteins, Prevention of membrane leakage, Protein stabilization

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3. Heat shock protein genes• Typical response to heat stress is a decrease in

the synthesis of normal proteins, accompanied by an accelerated transcription and translation of new proteins known as heat shock proteins (HSPs)

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Protein class Size (kDa) Location HSP100 100-114 cytoplasm HSP90 80-94 cytoplasm, ER HSP70 69-71 ER, cytoplasm, mitochondria HSP60 10-60 chloroplasts, mitochondria smHSP 15-30 cytoplasm, chloroplast, ER, mitochondria 64

4. Transcription factors validated under field conditions4. Transcription factors validated under field conditions

AtDREB1A – Groundnut, Rice, Potato, Pigeon pea GCP support (CGIAR/ICRISAT/JIRCAS/IRRI/University of Tsukuba)

AtDREB1A – Groundnut, Rice, Potato, Pigeon pea GCP support (CGIAR/ICRISAT/JIRCAS/IRRI/University of Tsukuba)

HsfA1 – tomato (Nover’ group)HsfA1 – tomato (Nover’ group)

OsDREB 1A – Rice (Yamaguchi Shinozaki and Shinozaki, 2004)OsDREB 1A – Rice (Yamaguchi Shinozaki and Shinozaki, 2004)

Shinozaki, 2004

DREB 1A – Soyabean, Few vegetables (AVRDC)DREB 1A – Soyabean, Few vegetables (AVRDC)

SNAC – Rice (Xiong et al., 2006)SNAC – Rice (Xiong et al., 2006)

NF-Y – Maize (Nelson et al., 2007)NF-Y – Maize (Nelson et al., 2007)

Bacterial RNA chaperon (CspA)-maizeBacterial RNA chaperon (CspA)-maize

Plant nuclear factor Y (NF-Y) Plant nuclear factor Y (NF-Y) confer drought tolerance in maizeconfer drought tolerance in maize

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Genetic Engineering approach

Can loose over 95%

water content and

survive for prolonged

periods

Survive at a RWC of

4%, while the lethal

RWC of most of the

crop plants and

mesophytes is 30-50%[32 % Pegion pea, 50% Soyabean ]

Sinclari (1980)

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Classified into 3 groups

1.Ferns [Selaginella lepidopglla]

3. Angiosperms (17geners)

[Xerophyta , Myrothamnus]

2. Bryophytes [Tortula sps]

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Taishi et al, 2006

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An integrated approach to develop crops for climate change

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Thank U

It i s ea sIt i s ea s y t o y t o wa s t e wa s t e

But d iBut d i f f i c u l t f f i c u l t t o t o p r op ro du c edu c e

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