Crops coping with water scarcity

CHIARA TONELLI

Università degli Studi di Milano

Global Trends – Impact for Agriculture

2 Productivity needs to double until 2030

Population [billion]

Total agricultural area per head [m²]

4,300 2,200 1,800

1960 2005 2030

3.0 6.5 8.3

World oil demand [billion barrel]

GNI/capita [1,000 USD]

Caloric intake of animal proteins [kcal]

Population growth

Increasing energy demand

Rising standards of living

India

China

Germany

France

US

Brazil

35

30

41

2005

2025

2035

POPULATIONS ARE INCREASING

Is there enough land?

3.2% of land

Land29.0%

Water70.9%

Amount of land needed to provide

for global energy demand based on

current energy content of the

biomass crop Miscanthus

AMBIO 23,198

(Total Land surface 13,000 M Ha)

Cereal4.6% Pasture

& Range

23.7%

30.5%

Other crops6.9%

Nonarable34.4%

Somerville, Curr. Bio, 17: R115-119, 2007

Forest & Savannah

Total surface area

of the Earth

Land surface area

•This map showing which of three key climate factors most limits plant growth in an area

•Red = water; Green = sunlight; Blue = temperature).

•In many places, these factors are co-limiting ( = mixed colours).

Limits to plant growth (water, sunlight, temperature)

Source NASA Earth Observatory

Crop Productivity: solutions need to address

primary constraints of a given system

Seed and Germplasm Quality

Local adaptation

Traits

Nutrient uptake and use

Photosynthetic

efficiency

Water-use

efficiency

Weeds Bugs

Disease

Plant

Architecture

and maturity

Heterosis

More production with:

• less water

• less fertilizer

• less chemicals

• not much more land

• more extreme weather

• need better varieties

• need better agronomy

THE WORLD IS GETTING WARMER

The major plant abiotic stresses are:

Abiotic stress is defined as the negative impact of non-

living factors on the living organisms in a specific

environment.

• flood

• drought

• high or low temperatures

• excessive soil salinity

• inadequate mineral in the soil

• too much or too little light

Cotton Abiotic Stress Tolerance: Case Study

Cotton is sensitive to various abiotic stresses

throughout the season

Emergence First square First bloom Peak bloom Open boll

Slow development,

uneven stand

Slow development,

square and boll drop

Slow boll development,

reduced quality

Cold Cold Drought

Poor fertilization,

boll drop

Heat

M. Metzlaff, Bayer CropScience

Stress limits plant productivity

• Abiotic stresses significantly decrease crop yield affecting both plant growth and seed production

http://www.fao.org/nr/water/

Drought ranks as the single most common cause of

severe food shortages in developing countries

Freshwater is a very limited resource

Source: FAO 2002; Crops and drops: make the best use of water for agriculture

World water distribution

Areas of physical and economic water scarcity

Physical water scarcity exists when physical access to water is limited.

Economic water scarcity exists when a population does not have the necessary monetary

means to utilize an adequate source of water. Economic water scarcity is about a unequal

distribution of resources for many reasons, including political and ethnic conflict.

Source: FAO 2006

Increase in soil salinity is another big problem associated to water

scarcity

http://www.fao.org/nr/water/

Agriculture makes the biggest demands on fresh water,

followed by industry and household use

21 %

69 %

10%

Contribution of different crops to the global virtual water content

(volume of water used in the production of a good or service)

A. Y. Hoekstra · A. K. Chapagain,Water Resour. Manage. (2007) 21:35–48

VIRTUAL-WATER CONTENT: volume of freshwater used to obtain a product,

measured at the place where it was actually produced

Designed byTimm Kekeritz from the study: Chapagain, A.K. and Hoekstra, A.Y. (2004), Water footprints of nations, Value of Water

Research Report Series No. 16, UNESCO-IHE, Delft, the Netherlands.

The water footprint of a person, company or nation is defined as the total volume

of freshwater that is used to produce the commodities, goods and services

consumed by the person, company or nation.

Average national water footprint per capita (m3/capita/yr).

A. Y. Hoekstra · A. K. Chapagain,Water Resource Management (2007) 21:35–48

Possible strategies

improvement in irrigation efficiency

desalination of sea-water

cultivation of species with relatively low water requirements

improvement of plant “water use efficiency” through selection, breeding

or genetic engineering approaches

improvement of plant performance and yield under drought conditions

through selection, breeding or genetic engineering approaches

Dehydration tolerance

Drought resistance strategies

Dehydration avoidance Maintenance of plant function in a

dehydrated state (osmotic adjustment,

decreased cell size)

Resurrection plants

Maintenance of high water status under

drought (efficient root system, reduced

transpiration, reduced evaporation)

Breeding programs

Dehydration tolerance mechanisms: osmotic adjustment

osmotic adjustment: a net increase in the number of solutes particles present in the plant cell

Solutes that contribute to osmotic adjustments are:

Dehydration avoidance mechanisms:

reduction of transpiration through stomata closure

Dehydration avoidance mechanisms:

reduction of evaporation through cuticle thickening

How biotecnology can be used to obtain drought

resistant plants?

• which gene? functional or regulatory gene?

• which promoter? constitutive or inducible?

• in which way? over-expression or down-regulation?

Technology transfer

from model plants to crops

Arabidopsis thaliana as a model plant

small genome (about 130 Mbp, 5 chromosome, 27,000 genes)

the first plant genome to be sequenced (completed in 2000)

rapid life cycle (2 months from germination to mature seed)

small size convenient for cultivation in small spaces

many seeds (several thousand)

high transformation efficiency

genomics resources (insertion mutants collections, genome arrays etc.)

Transfer of Arabidopsis genes and their

regulatory sequences to crops

Identification of othologs in crops through bioinformatic search and modulation of their

expression

Preliminary study of function of crop orthologs and their regulatory sequences in

Arabidopsis

Different strategies of technology transfer

Functional proteins

Regulatory proteins

Functional proteins

Regulatory proteins

control drought

RNA extraction in this way in Arabidopsis ~1000 genes

identified!!!

Identification of genes involved in drought stress response

Hybridization

to microarray

Laser excitation

at dye specific Hz

Laser emission Computer calculates

ratio of intensity

Shinozaki and Yamaguchi-Shinozaki, 2007

2nd Signalling

Molecules

Stress stimuli

Proteins involved in

CELLULAR PROTECTION TRANSCRIPTION

FACTORS

STRESS-ACTIVATED

GENES

Proteins involved in

CELLULAR PROTECTION

AB

A, E

TH

YLE

NE

, S

A

Targets

activation

Ca++ 2nd Messangers

Phosphoproteins

Generation of

2nd messangers

Phosphorilation

cascade

The Plant Response to Abiotic Stress

RESPONSE Tolerance Growth

arrest Death

Multiple Primary Receptors

Signal

perception

Functional proteins

Regulatory proteins

Which gene? coding a functional protein

Umezawa et al., 2006

Engineering drought tolerance using functional proteins

Pr ProDH

Modification of proline biosynthesis to accumulate

more proline

1. P5CS for synthesis

2. ProDH for degradation

overexpression

antisense

1

2

Functional proteins

Regulatory proteins

Overexpression

Which strategy?

Yamada et al., Journal of Experimental Botany, Vol. 56, No. 417, pp. 1975–1981, July 2005

pCaMV35S

pCaMV35S OsP5CS

AtP5CS

Constitutive expression of AtPC5S or OsP5CS improves petunia response

to drought stress

Young (10-d old) wild-type and

transgenic petunia plants that

were not watered for 14 d.

Photographs show revived

plants 7 d after watering.

• tobacco: when P5CS was overexpressed the plants synthesized 10–18

times more Pro than the control plants and were more tolerant to water

stress (Kavi Kishor et al., 1995)

• rice plants that contained overexpressed P5CS were tolerant to salt and

water stress (Zhu et al., 1998)

• Arabidopsis: AtP5CS antisense transgenic plants were more sensitive to

low humidity stress, survived by adding L-Pro (Nanjo et al., 1999b)

Similar results in other species concerning P5CS

Functional proteins

Regulatory proteins

antisense

Which strategy?

Pr ProDH

Modification of proline biosynthesis to accumulate

more proline

2. ProDH for degradation

antisense

2

pCaMV35S AtProDH

Constitutive down-regulation of AtProDH improves Arabidopsis response to

low humidity and salt stress

Nanjo et al., 1999,

FEBS Letters 461, 205-210

before low humidity treatment

after low humidity treatment

after rehydration

Constitutive down-regulation of AtProDH improves Arabidopsis response to

freezing stress (-7°C)

Functional proteins

Regulatory proteins

Which gene? coding a regulatory protein

Umezawa et al., 2006

Engineering drought tolerance using regulatory proteins: transcription factors

http://evolution.berkeley.edu

many functional proteins only 1 regulatory protein

Functional proteins

Regulatory proteins : constitutive promoter

Which promoter? constitutive

Drought, Salt Cold

Stress response, Stress tolerance

Shinozaki & Shinozaki Molecular responses to dehydratation and low temperature: differences and cross-talk between two stress signalling pathways

Curr. Op. Plant Biol, 2000, 3:217-223

Gene expression in response to osmotic stress

rd29A

cis-elements

Activation of rd29A in response to osmotic stress

Shinozaki & Shinozaki Molecular responses to dehydratation and low temperature: differences and cross-talk between two stress signalling pathways

Curr. Op. Plant Biol, 2000, 3:217-223

Liu et al. (1998) Plant Cell 19:1391-1406

Constitutive expression of DREB1 in Arabidopsis

transgenic wild type

control

drought stress

Transgenics are more drought tolerant than wild type

BUT

dwarf phenotype

growth retardation

under the control of a promoter that confers expression in any organs in

any growth conditions

DREB1 pCaMV35S

Functional proteins

Regulatory proteins : stress inducible

promoter

Which promoter? inducible

rd29A DRE/CRT ABRE

cold drought, salt

DREB1 DRE/CRT ABRE

Native promoter for rd29A

Artificial promoter for DREB1

Kasuga et al. (1999) Nature Biotech. 17:287-291

DREB1 pRD29A

under the control of a promoter that confers high expression only in response to

abiotic stress

transgenics are more drought tolerant than wild type

AND

their growth is NOT affected

Inducible expression of DREB1 in Arabidopsis

transgenic wild type

Many genes for drought tolerance identified -rice -Brassica -corn

Estimated commercial release in 2014

Non-GMO GMO

Monsanto