J.P. Métraux, C. Chassot, T. Genoud, S. Heck, C. Nawrath
Nonglak Parinthawong. Département de Biologie, Université de Fribourg, 3 Rte A. Gockel, 1700 Fribourg, Suisse

Exposure of plants to various microorganisms, chemicals or physical stress can induce resistance to a broad spectrum of pathogens. Induced resistance is expressed locally and distally from the initial site of stress exposure. Salicylic acid (SA) is an endogenous signal involved in the regulation of this systemic acquired resistance. Besides SA other signals such as jasmonic acid or ethylene are also involved in the induction of plant defences. Various examples show that specific stimuli lead to specific responses, with interferences or crosstalks between signal transduction pathways. Besides induced defences, plants also have constitutive barriers that protect against invading organisms. A classical example is the cell wall and its cuticular layer. This notion was recently tested in our group by over expressing a fungal cutinase in Arabidopsis. The cuticular layer is strongly decreased in such plants but their resistance to the necrotrophic pathogen Botrytis cinerea is increased. This counterintuitive result indicates that the absence of cuticle is perceived by the pathogen. Thus, the cuticle might constitute a source of possible signals for the activation of pathogenicity in the invader or for the induction of host resistance. These hypotheses are currently being studied. Another challenge is to adequately represent the signalling network for induced resistance. An example will be given how this problem can be approached using a digital formalism.