Plant Virus Silencing Suppressors and RNA Silencing in Plants

Abstract Plants use ribonucleic acid (RNA) of virus origins to produce small interfering RNAs (siRNAs) that guide sequence‐specific destruction of viral RNAs through a process termed RNA silencing. In addition to siRNAs, antiviral RNA silencing requires the participation of at least four families of plant proteins, namely the dicer‐like (DCL) nucleases that process virus‐specific double‐stranded (ds) RNA to siRNAs, Argonaute proteins (AGO) that use siRNAs as the sequence‐specific guide to cleave (slice) complementary single‐stranded viral RNA, as well as dsRNA‐binding proteins (DRBs) that assist DCL processing and/or DCL‐AGO communication, and RNA‐dependent RNA polymerases (RDRs) that produce a subset of dsRNA substrates of DCLs by converting viral ssRNAs into dsRNAs. To survive the RNA silencing‐based plant defence, plant viruses have evolved to encode strong suppressors of RNA silencing (VSR). Known targets of VSRs include all major steps/components of the RNA silencing pathway(s). Key Concepts: RNA silencing is an RNA‐mediated, sequence‐specific surveillance system in plants and other eukaryotes. The sequence specificity of RNA silencing is conferred by siRNAs generated through the processing of dsRNAs originated from viruses and other molecular parasites. RNA silencing is analogous to RNA interference (RNAi) in animals. It is a highly conserved mechanism of genome defence in almost all eukaryotic organisms. Evolutionary successful viruses encode VSRs to engage diverse components of the RNA silencing pathway and subvert this robust defence mechanism.