LysM effectors of fungal plant pathogens contribute to virulence in various manners

PR4.82 LysM effectors of fungal plant pathogens contribute to virulence in various manners Anja Kombrink, Jason J. Rudd, Bart P.H.J. Thomma Laboratory of Phytopathology, Wageningen University, 6708 PB Wageningen, Netherlands LysM effector genes are found in the genomes of a wide range of fungal species. LysM effectors are secreted proteins that contain a varying number of LysM domains and no other recognizable protein domains. LysM domains are carbohydrate-binding modules that occur in various proteins that are produced by a variety of organisms. Ecp6 is the first characterized LysM effector that was isolated from the tomato leaf mould fungus Cladosporium fulvum and that is instrumental for fungal virulence. Carbohydrate binding assays demonstrated that Ecp6 specifically binds chitin, the major constituent of fungal cell walls that acts as microbial-associated molecular pattern (MAMP) that triggers immune responses upon recognition by the host. We demonstrated that the chitinbinding effector Ecp6 can compete with plant receptors for chitin binding, and thus prevents the activation of immune responses. Two orthologues of Ecp6 were identified in the fungal wheat pathogen Mycosphaerella graminicola, of which one suppresses chitin-induced immune responses in a similar fashion as Ecp6. Interestingly, unlike Ecp6, both M. graminicola LysM effectors were able to inhibit degradation of fungal hyphae by plant chitinases. Many fungal genomes carry multiple LysM effector genes that share only low sequence conservation and encode varying LysM domain numbers per molecule. Therefore, we hypothesize that different fungal LysM effectors are likely to bind different carbohydrate substrates, exert other functions, or are active in other stages of the fungal life cycle than plant infection. We will report on our most recent findings on LysM effector substrates and functions.