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

Abstract

Small 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 pathogen Botrytis cinerea that is required for pathogenicity and cross-kingdom RNAi. B. cinerea bcrdr1 knockout (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 that bcrdr1 ko mutants were compromised in cross-kingdom RNAi. Moreover, blocking seven pathogen cross-kingdom small RNAs by expressing a short-tandem target mimic RNA in transgenic Arabidopsis thaliana led to reduced infection levels of the fungal pathogen B. cinerea and the oomycete pathogen Hyaloperonospora 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.

A journey into the world of small RNAs in the arbuscular mycorrhizal symbiosis

“…The process where mobile sRNAs are transported between distantly related organisms leading to silencing the expression of target genes in the interacting partner through RNAi is known as crosskingdom RNAi (ckRNAi, Cai et al, 2018a) and has been described in plant and animal systems (Buck et al, 2014;Cai et al, 2019;Zhao et al, 2021) ckRNAi as a widespread defense strategy to suppress virulence targets in the invading organism (Zhang et al, 2016;Cai et al, 2018b;Hou et al, 2019;Zhu et al, 2022). Equally, evidences of sRNA movement from pathogens to plants, leading to the RNAi-mediated suppression of plant defense, pointed to ckRNAi as an evolutionarily conserved virulence mechanism (Weiberg et al, 2013;Wang et al, 2016;Xu et al, 2022;Cheng et al, 2023).…”

“…In plants, numerous studies have confirmed ckRNAi as a widespread defense strategy to suppress virulence targets in the invading organism (Zhang et al ., 2016; Cai et al ., 2018b; Hou et al ., 2019; Zhu et al ., 2022). Equally, evidences of sRNA movement from pathogens to plants, leading to the RNAi‐mediated suppression of plant defense, pointed to ckRNAi as an evolutionarily conserved virulence mechanism (Weiberg et al ., 2013; Wang et al ., 2016; Xu et al ., 2022; Cheng et al ., 2023).…”

“…On the fungal side, it will be crucial, though challenging due to their nature of obligate biotrophs, to functionally dissect the rich repertoire of AGO and RdRp to verify whether specific components are required for symbiosis in analogy to what is emerging from fungal pathogens (Cheng et al ., 2023). We also need to decipher the role of the sRNA populations in AM fungi to understand how they influence fungal gene expression and, as a consequence, fungal biology and symbiotic functions.…”