FsK RNAi

The soil-borne beneficial fungal endophyte <em>Fusarium solani</em> strain K (FsK) confers resistance and/or tolerance to biotic and abiotic stress in tomato and promotes plant growth in <em>Nicotiana benthamiana</em>. Characterizing its core RNAi machinery, we determined that FsK encodes two Dicer-like (DCL) endonucleases, 2 Argonaute (AGO) proteins and 4 RNA-dependent RNA (RDR) polymerases. FsK DCLs process endogenously-transcribed or exogenously-applied double stranded RNAs (dsRNAs) into short interfering RNAs (siRNAs) which lead to the degradation of homologous mRNAs. However, no RDR-mediated transitivity on the targeted mRNA or RNA-directed DNA methylation (RdDM) on the cognate DNA takes place in the fungus. Evidence that FsK colonization of <em>N. benthamiana</em> can lead to the induction of systemic silencing and RdDM of a host reporter gene is supported small RNA sequencing data.