Proteolytic control of the RNA silencing machinery

Studies in plants were often pioneering in the field of RNA silencing and revealed a broad range of small RNA (sRNA) categories. When associated with ARGONAUTE (AGO) proteins, sRNAs play important functions in development, genome integrity, stress responses, and antiviral immunity. Today, most of the protein factors required for the biogenesis of sRNA classes, their amplification through the production of double-stranded RNA, and their function in transcriptional and posttranscriptional regulation have been identified. Nevertheless, and despite the importance of RNA silencing, we still know very little about their posttranslational regulation. This is in stark contrast with studies in metazoans, where different modifications such as prolyl hydroxylation, phosphorylation, sumoylation, ubiquitylation, and others have been reported to alter the activity and stability of key factors, such as AGO proteins. Here, we review current knowledge of how key components of the RNA silencing machinery in plants are regulated during development and by microbial hijacking of endogenous proteases.