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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?
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