An overview of antiviral RNA silencing in plant: Biogenesis, host-virus interaction and potential applications

Abstract

Small RNA molecules play a crucial regulatory role in maintaining genome stability as well as developmental regulations through a set of complex and partially overlapping pathways in a wide range of eukaryotic organisms. Active in both cytoplasm and nucleus, RNA interference regulates eukaryotic gene expression through transcriptional repression by epigenetic modification and interaction with transcription machinery. Small interfering RNAs (siRNAs/miRNAs) of 21-24 nucleotides constitute the innate defence arm against a variety of pathogens, especially viruses. Plant viruses with either DNA or RNA genomes are subjected to small RNA-directed RNA degradation. Additionally, DNA viruses are subjected to another line of defence through 'RNA-directed DNA methylations' (RdDM). On the other hand, viral-encoded proteins, called silencing suppressors (VSRs), are known to counter the defence machinery, and therefore the virus can evade the host surveillance system. Some plant viruses additionally adopt certain strategies like acquiring silencing resistant structures (some RNA virus) to evade the RNA silencing machinery and thereby shaping the viral as well as the host genome. Recently, it has been reported that particular viral proteins and viral siRNAs contribute directly to pathogenicity by interacting with certain host proteins or RNAs. Transcriptional regulation of host gene by small RNA of viral origin plays important role in pathogenesis and symptom development. Small regulatory RNAs of cellular rather than pathogen origin have also been found to play a broad role in improving the basal defence in the case of plant-virus interaction. This chapter provides key insights into the complex intricate machinery of diverse RNA silencing mechanisms, describes various evolutionary diverse strategies of viral silencing suppressors at various steps, offers a broader view of host recovery following virus infection and finally suggests the possible applications of RNA silencing to generate virus resistant plants.