The Rhizoctonia solani RsLysM and RsRlpA effector proteins contribute to virulence 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 diseases of seedlings and root rot, although it can infect plants in any stage. Despite the severity of this disease, many aspects in R. solani infection biology still remain to be elucidated. Here we investigated the role of two effector candidates, predicted from the genome of a R. solani AG2-2IIIB strain that uses sugar beet as a host. Gene expression analysis showed that genes encoding for a LysM effector and a rare lipoprotein-A-like protein (RsRlpA) were induced upon early infection stages. When heterologous expressed in Cercospora beticola the two genes contributed to virulence. The RsLysM effector showed chitin- binding affinity and suppression of chitin-triggered immunity but could not protect hyphae from hydrolysis. The RsRlpA effector suppressed hypersensitive response in Nicotiana benthamiana leaves. Overall, this study provides us with valuable information on R. solani infection biology, implying that this organism relies on mechanisms similar to hemibiotrophic pathogens in order to establish a successful infection.