VIRAL SUPPRESSION OF RNA SILENCING IN PLANTS

RNA silencing in plants is a mechanism involved in the regulation of gene expression that also serves as antiviral defense. This process is induced by the presence of double-stranded RNA molecules that activate a cascade of enzymatic processes and results in the inhibition or suppression of nucleic acid molecules through specific interactions. To counteract this defense mechanism, viruses encode in their genome RNA silencing suppressor proteins that can interfere with any step of the RNA silencing pathway. These RNA silencing suppressor proteins are highly diverse in both sequence and structure and have often been linked to synergistic interactions in mixed infections. Although the details of the molecular mechanisms of suppression are completely known in very few cases, most viral suppressors counteract RNA silencing by acting on RNA molecules involved in the silencing pathway or by interacting with its protein components. This review discusses the different strategies of viral RNA silencing suppression currently known and their possible involvement in the pathogenesis and viral synergism processes primarily in RNA viruses, because they are the majority among plant viruses.