A fungal RNA-dependent RNA polymerase is a novel player in plant infection and cross-kingdom RNA interference

Abstract

AbstractSmall RNAs act as fungal pathogen effectors that silence host target genes to promote infection, a virulence mechanism termed cross-kingdom RNA interference (RNAi). The essential pathogen factors of cross-kingdom small RNA production are largely unknown. We here characterized the RNA-dependent RNA polymerase (RDR)1 in the fungal plant pathogenBotrytis cinereathat is required for pathogenicity and cross-kingdom RNAi.B. cinerea bcrdr1knockout (ko) mutants exhibited reduced pathogenicity and loss of cross-kingdom small RNAs. We developed a novel “switch-on” GFP reporter to study cross-kingdom RNAi in real-time within the living plant tissue which highlighted thatbcrdr1ko mutants were compromised in cross-kingdom RNAi. Moreover, blocking seven pathogen cross-kingdom small RNAs by expressing a short-tandem target mimic RNA in transgenicArabidopsis thalianaled to reduced infection levels of the fungal pathogenB. cinereaand the oomycete pathogenHyaloperonospora arabidopsidis. These results demonstrate that cross-kingdom RNAi is significant to promote host infection and making pathogen small RNAs an effective target for crop protection.