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In plants, fluctuating environmental conditions trigger various responses at many levels, including gene expression, protein regulation and metabolism. The quantitative outcome of these responses is the result of the activity of complex multigenic networks. Thus, the plant responses to the environment are seen as multigenic traits resulting from variation and selection during evolution. Furthermore, we need to understand how genetic variation within and between species contributes to creating robustness to environmental stress responses. Among these responses, phenotypic plasticity plays an essential role. This plasticity covers all the developmental and morphogenetic modifications that change the growth, the shape or the number of certain organs (e.g. leafs, roots, seeds) in response to environmental signals. Interestingly, plant responses to stresses of various origins, biotic (pathogens, insect pests or beneficial microbes) or abiotic (e.g. drought, salt, temperature and light), share many common features, in the perception mechanisms and signalling. Moreover, it is established that the nutritional status of a plant can have a dramatic effect on its sensitivity to pathogen attacks (for iron and nitrogen for example). When submitted to simultaneous stresses, the plant develops other emerging responses than those obtained in a simplified model where only one variable is fluctuating. The development of integrated projects on the thematic “biotic and abiotic stress, convergences and divergences” is therefore of a key interest. Availability of validated models of regulatory networks will enable rational plant engineering, via genetic selection or synthetic biology techniques, to produce crop plants able to produce more sustainable yields in a fluctuating environment.

Important scientific issues in this field are for instance

• Tolerance to abiotic stresses (e.g. drought, salt, temperature)
• Resistance to biotic stresses (e.g. bacterial, viral or fungal pathogens)
• Growth with lower nutrient inputs (decreased nitrogen fertilizers) and interactions with symbionts