A multifunctional LysM effector ofBotrytis cinereacontributes to plant infection

Abstract

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.

Non-proteinaceous effectors of Botrytis cinerea : Contributions and modes of action during the interaction with hosts

“…This study also showed up-regulation of the BcLysM1 gene exclusively in infection cushions in the early phase of infection, and demonstrated an additional role for the BcLysM1 effector in adhesion to the host besides the chitin-binding feature that is commonly shared among fungal LysM effectors (Crumière et al, 2022). Additionally, the agar plugs containing fungal hyphae are likely to contain CDIPs and phytotoxic SMs that have been produced and accumulated in the pre-culture (where the agar plugs are excised from), which could boost the fungal infection from the very early phase of the interaction.…”

“…Choquer et al (2021) reported that genes related to the production of SMs, cell death inducing proteins and cell wall-degrading enzymes, were up-regulated in infection cushions in vitro and in planta. A recent study reported that a ∆BcLysM1 mutant displayed a lower disease incidence and retarded expansion of the secondary lesions only when the bean leaves were inoculated with mycelial plugs, while the same mutant was similarly virulent as the WT fungus when inoculated with conidia (Crumière et al, 2022).…”

The Botrytis cinerea transglycosylase BcCrh4 is a cell death‐inducing protein with cell death‐promoting and ‐suppressing domains

“…Further analyses showed that inhibition of cell death and PTI by the BcCrh4 75–126 fragment was dose‐dependent, suggesting that both epitopes compete on the same target. This mode of action resembles the sequestration of chitin oligomers and prevention of PTI by the Cladosporium fulvum LysM‐domain Ecp6 effector (De Jonge et al, 2010) and B. cinerea BcLysM1 putative LysM effector (Crumiere et al, 2022). The two domains probably compete for the same plant target since co‐infiltration of BcCrh4 75–126 with BcCrh4 22–41 and suppresses the induction of cell death and plant immune responses.…”