TheRhizoctonia solaniRsLysM and RsRlpA effector proteins contribute to virulence by suppressing chitin-triggered immunity and hypersensitive response

Abstract

Rhizoctonia (in Greek "root-killer") species and particularly R. solani attacks a broad range of plant species and crops. It belongs to Basidiomycota and is a soil-borne pathogen causing mainly damping-off in seedlings, although it can infect plants in any stage. It does not form any kind of asexual spores while the sexual form (Thanatephorus cucumeris) is extremely rare. However, it forms microsclerotia, able to survive in soil and plant debris for a long period and under harsh environmental conditions. Despite the severity of this disease, many aspects in R. solani infection biology still remain to be elucidated. In this study, we investigated the role of two effector candidates, derived from a R. solani AG2-2IIIB strain isolated from infected sugar beet plants. Gene expression analysis showed that genes encoding for a LysM effector and a RlpA-like protein were induced upon early infection stages, while their heterologous expression in Cercospora beticola contributed to virulence. Furthermore, the RsLysM effector showed chitin binding affinity, suppressing chitintriggered immunity but could not protect hyphae from hydrolysis. The RlpA-like effector is homologous to a papain-like inhibitor and to a barwin-like endoglucanase, while our data showed that it was able to suppress hypersensitive response in Nicotiana bethamiana leaves. Overall, this study provides us with valuable information on R. solani infection biology towards understanding the molecular mechanisms in this pathosystem.