SummaryThe plant hormones ethylene, jasmonic acid and salicylic acid have interconnecting roles during the response of plant tissues to mutualistic and pathogenic symbionts.We used morphological studies of transgenic-or hormone-treated Populus roots as well as whole-genome oligoarrays to examine how these hormones affect root colonization by the mutualistic ectomycorrhizal fungus Laccaria bicolor S238N.We found that genes regulated by ethylene, jasmonic acid and salicylic acid were regulated in the late stages of the interaction between L. bicolor and poplar. Both ethylene and jasmonic acid treatments were found to impede fungal colonization of roots, and this effect was correlated to an increase in the expression of certain transcription factors (e.g. ETHYLENE RESPONSE FACTOR1) and a decrease in the expression of genes associated with microbial perception and cell wall modification. Further, we found that ethylene and jasmonic acid showed extensive transcriptional cross-talk, cross-talk that was opposed by salicylic acid signaling.We conclude that ethylene and jasmonic acid pathways are induced late in the colonization of root tissues in order to limit fungal growth within roots. This induction is probably an adaptive response by the plant such that its growth and vigor are not compromised by the fungus.

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Les glucosinolates des produits naturels riches en soufre qui, après hydrolyse par des thioglucosidases appelées myrosinases, produisent plusieurs produits différents (isothiocyanates, thiocyanates et nitriles), ces produits d'hydrolyse ont de nombreuses propriétés biologiques différentes, notament dans la défense des plantes contre les attaques des ennemis naturels. Nous résumons ici des études menées chez Brassica qui ont fourni des preuves moléculaires sur la biosynthèse des glucosinolates leurs régulations à différent niveaux et le contrôle génétique de la variation naturelle de leur accumulation. AbstractGlucosinolates are natural products sulfur-rich that upon hydrolysis by thioglucosidases called myrosinases produce several different products (isothiocyanates, thiocyanates, and nitriles), these hydrolysis products have many different biological properties, especially in the defense of plants against the attacks of natural enemies. Here we summarize studies in Brassica that have provided molecular evidence on the biosynthesis of glucosinolates, their regulation at different levels and the genetic control of the natural variation of their accumulation.