A multifunctional LysM effector ofBotrytis cinereacontributes to plant infection

Summary LysM effectors are suppressors of chitin-triggered plant immunity in biotrophic and hemibiotrophic fungi. Their role in necrotrophic fungi is unclear as these last are known to activate plant defenses and induce cell death. To characterize the role of the BcLysM1 gene encoding a putative LysM effector in the necrotrophic fungus Botrytis cinerea , its expression was followed by transcriptional fusion and by RT-qPCR in planta . Two tagged-recombinant proteins were produced, and two independent deletion strains were constructed and characterized. BcLysM1 is induced in the early phase of infection, and more specifically in multicellular appressoria called infection cushions. The BcLysM1 protein binds the chitin in the fungus cell wall and protects hyphae against degradation by external chitinases. It is also able to sequester chitooligosaccharides and to prevent them from inducing ROS production in A. thaliana. Using mycelium as inoculum, deletion strains show a delay in infection initiation and a default in adhesion to bean leaf surfaces. This study demonstrates for the first time a dual role for a LysM effector in mycelium adhesion on the plant and in host defenses suppression, both of them occurring during the asymptomatic phase of infection by a necrotrophic fungus.