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The infection cushion: “a fungal weapon for plant biomass destruction” ?

Mathias Choquer: University Lyon 1

<div>The infection cushion (IC) is a structure differentiated by several phytopathogenic fungi in order to penetrate the host plant. It is described as a melanized appressorium, made of several aggregated hyphae that induce an oxidative burst. Few molecular data have been produced to further characterize the role of this fungal structure in plant pathogenicity. Here we analyzed the transcriptome and the secretome of the IC in <em>Botrytis cinerea</em>. This necrotrophic fungus causes gray mold on more than a thousand plant species, such as grapevine or vegetable crops. Our data revealed a significant enrichment in membrane transporters and secreted proteins suggesting a high potential of nutrition and secretion, respectively. Indeed, we confirmed that IC is a structure dedicated to the production of secreted lytic enzymes such as proteases, xylanases, cellulases and pectinases. Several biosynthetic pathways are strongly induced in IC, including that of melanin and other secondary metabolites, among which botrydial and botcinic acid, the two major phytotoxins produced by <em>B. cinerea</em>. At last, and surprisingly, the transcriptomic data and labelling results suggest that chitin may be deacetylated in the cell wall of IC, a modification that is described in biotrophic fungi as a mechanism to escape the host plant immunity. Altogether these results suggest that IC may not be useful for penetration of the fungus only, but that it could also contribute to necrotrophy.</div>