Biogenesis and function of virus-derived small interfering RNAs in plants

RNA silencing is a deeply conserved mechanism that operates in most eukaryotes. A hallmark of RNA silencing is the processing of double-stranded RNA (dsRNA) precursors into 21- ~24-nucleotide (nt) small RNAs that function as sequence-specific cellular regulators. One of the well-established roles of RNA silencing is antiviral defense in plants. The virus-derived small RNAs found in the infected host cells serve as a manifestation that viral RNAs are targeted by the host RNA silencing machinery. On the other hand, many viruses encode proteins that suppress the activities of host silencing machinery, reflecting a viral counter-defense strategy evolved during the long-standing virus-host arms race. In many cases, viral disease symptoms are attributable, at least in part, to the interference of the host endogenous small RNA pathways by the virus-encoded silencing suppressors. During the last few years, significant advances have been made in our understanding of the host RNA silencin