Download White paper on `Crop Productivity`

WHITE PAPER
European Plant Science Organisation
www.epsoweb.org
Crop Productivity for Food – from models to crops
Brussels, 29.8.2010 - This white paper on ‘Crop Productivity for Food – from models to crops’
is the outcome of the EPSO workshop on Plant Productivity for Food held in Ghent, 7-8.9.2009.
The aim of the workshop was to serve as a think-tank on how basic information on
mechanisms that control plant growth and tolerance to abiotic stress can be best translated to
improve crop productivity. Some 50 participants from academia as well as from private
enterprises participated in the workshop.
The following major issues were addressed during the workshop:
- Mechanisms controlling growth under normal conditions
- Mechanisms conferring tolerance to abiotic stress
- What can biodiversity teach us?
- How to translate research on model systems to crop plants?
- How can crop productivity further be improved?
The scientific presentations clearly demonstrated the enormous progress made in understanding the
molecular mechanisms that drive plant productivity under optimal as well as environmental stress
conditions. In numerous cases engineering single genes or combinations of genes (eg. to bypass
photorespiration) was shown to enhance plant growth. Understandingly much of this work has been
done in model plants, with Arabidopsis as the leading system, but there is an observable tendency to
perform more research on crops. However, the lectures also made it clear that plant growth is a highly
complex process in which many inputs such as photosynthesis, water and nutrient availability are
integrated and translated into developmental programs that orchestrate growth. Similarly responses of
plants to abiotic stress conditions such as drought; phosphor- or nitrogen deficiency are multifactorial.
For this reason the transfer of a single gene encoding a specific stress protein does not always results
in sufficient expression to produce useful tolerance, because multiple and complex pathways are
involved in controlling plant drought responses and because modification of a single enzyme in a
biochemical pathway is usually compensated by a tendency of plant cells to restore homeostasis.
Targeting multiple steps in a pathway may modify metabolite fluxes in a more predictable manner.
Another promising approach is therefore to engineer the overexpression of genes encoding stressinducible transcription factors. Transcription factors typically regulate several genes and are likely to
be used extensively in the next generation of genetically modified crops. Understanding the complexity
of the growth regulatory networks and of stress tolerance is a daunting challenge and will rely on the
continuous efforts of many scientists worldwide.
The scientific presentations were followed by discussions on how Europe should proceed in tackling
crop productivity. Following recommendations were made:
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Most research on plant growth and tolerance to abiotic stress is performed on Arabidopsis.
Nevertheless, most of the world’s food supplies are derived from cereals. During the discussion the
participants strongly supported that work on Arabidopsis is continued but also expressed the
opinion that more research has to be done on grasses and cereals.
The participants were divided whether the novel monocot model, Brachypodium distachyon would
become the ‘monocot equivalent’ of Arabidopsis. Its small genome size, ease to grown and short
generation time makes Brachypodium interesting. The scientific community working on
Brachypodium is rapidly growing and there are already a number of resources available (eg.
insertion mutant collections; tilling collections;…). However, the spectacular recent advances in
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genome sequencing also made crop plants such as corn and rice amenable for fundamental
research. The latter will be helped by available sequences and the larger collection of publicly
available germlines.
There is a great potential for Europe to further develop wheat. Wheat germplasm is publicly
available.
Continue to implement various “omics” technologies to facilitate plant breeding.
The genotype to phenotype relation is not-linear and in order to better understand how genes affect
growth related phenotypes, we need to enhance our ability to phenotype plants preferentially with
cellular resolution.
Also in the case of abiotic stress tolerance global analysis of gene expression in whole plants or
heterogeneous organs has greatly limited our understanding of how multi-cellular organisms cope
with environmental changes at the cellular level, and prevented the identification of key genes
involved in the regulation of subtle but significant cell-specific responses. Efforts to identify such
genes has to be strengthened with the support of novel techniques such as laser microdissection
followed by expression analysis. Furthermore a systematic analysis of plant regulatory regions to
identify novel stress-inducible tissue/cell-specific promoters to target proper tissue/cellular
expression could be undertaken in order to use them to control the intensity and time of expression
of the genes of interest used to transform crop plants.
Much of our understanding of growth related processes is based on transcriptome studies and
more efforts has to be invested in studying growth and tolerance to abiotic stresses at the
proteome and metabolome level.
Growth under ‘optimal’ as well as stress conditions is highly complex, involving the interaction of
many genes and their products. A full understanding of the growth regulatory circuits and defense
mechanisms of plants to stress will require a systems biology approach. More emphasis has to be
given to the development of methods to describe and utilize the often complex regulatory networks
that integrate developmental and environmental signals in growth responses and defense
reactions.
The gap between on one hand academic research (Petri disc based) and the other hand field
performance of a crop is too large. More realistic growth and stress assays need to be developed.
When possible genes need to tested directly in crops in greenhouse conditions that mimic as much
as possible field conditions. For example, crop plants are always grown in close proximity of each
other and we need to evaluate the performance of transgenic lines when multiple plants are grown
close to each other. Preferentially it should become considerably more easy to perform field
evaluation of transgenic crops. Also in the study of abiotic stress tolerance there is a gap between
experimental and field conditions. In the case of drought stress for example several methods for
imposing water stress conditions have been described for model plants such as Arabidopsis, most
of which rely on rapid drying of the soil within a few days or complete removal of plants from water
source. However such dehydration techniques are not relevant to cropping environments, where
deficits develop over a period of weeks, which allows time for acclimation at both the organ and
gene expression level. A serious effort that offers some guidelines towards a general water stress
phenotyping procedure for Arabidopsis has been initiated, but need to be implemened through the
preparation of a rigorous protocol for the imposition of mild water deficit over a prolonged period of
time, based on soil water content as driving variable. In addition it would be very interesting and
informative to study plant responses to a combination of water and heat stress, as these two
conditions often occur simultaneously in cropping environments.
The current focus on molecules should be extended to whole plant physiology. The use of
radioisotopes to study nitrogen and carbon fluxes (already used by ecologists) could provide novel
routes for crop improvement.
The development of plants with a more adapted root system is relatively unexplored. Building
imaging systems to evaluate root systems, so-called rhizotrons was considered priority. Such
systems would allow to study water use efficiency (WUE); nitrogen use efficiency (NUE) and
phosphate use efficiency (PUE).
As plants lose over 95% of their water via transpiration through stomata, the engineering of
stomatal activity is a promising approach to reduce the water requirement of crops and to enhance
productivity under stress conditions.
Modern crops have been selected for maximal yield performance in a given environment. The
progress in Next Generation Sequencing provides unprecedented opportunities to understand the
domestication process and to use this information to further improve crops.
Breeding could be advanced by the development of biomarkers that forecast events that take place
later in development.
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Plant engineering offers the ability to stack beneficial traits and research has to be initiated not only
to build the technology to combine gene but also to analyze which combination of traits can actually
be made.
There is a fairly good understanding of mechanism operating in source tissues (photosynthesis;
stress tolerance mechanisms) but little is known on the growth regulatory mechanisms in sink
tissues, such a meristems.
Given the importance of heterosis for food production, understanding its molecular basis remains
high priority.
Central data managing as was done by TAIR (www.Arabidopsis.org) is an enormous asset and
should be strongly supported.
Acknowledgements
EPSO wishes to thank Chiara Tonelli (University of Milano, Italy) and Dirk Inzé (VIB, Belgium) for leading the
development of this White Paper, as well as all workshop participants for their contributions during and following
the workshop.
Contacts
Chiara Tonelli
+39-02-5031-5008
[email protected]
Dirk Inzé
+32-933-13-806
[email protected]
EPSO Office
+32-2213-6260
[email protected]
Useful links
Crop Productivity workshop: http://www.epsoweb.org/workshop-plant-productivity-food-1
Communications webpage: http://www.epsoweb.org/epso-communications
EPSO member institutes and universities: www.epsoweb.org/about/members.htm
EPSO representatives: www.epsoweb.org/about/representatives.htm
About EPSO
EPSO, the European Plant Science Organisation, is an independent academic organisation that represents more
than 226 research institutes, departments and universities from 30 countries in Europe and beyond. EPSO’s
mission is to improve the impact and visibility of plant science in Europe. www.epsoweb.org