RNAi-mediated resistance to viruses: a critical assessment of methodologies.

In plants, RNA interference (RNAi)-based antiviral defense is mediated by multigenic families of Dicer-like enzymes generating small interfering (si)RNAs from double-stranded RNA (dsRNA) produced during replication and/or transcription of RNA and DNA viruses, and Argonaute enzymes binding viral siRNAs and targeting viral RNA and DNA for siRNA-directed posttranscriptional and transcriptional silencing. Successful viruses are able to suppress or evade the production or action of viral siRNAs. In antiviral biotech approaches based on RNAi, transgenic expression or non-transgenic delivery of dsRNA cognate to a target virus pre-activates or boosts the natural plant antiviral defenses. Design of more effective antiviral RNAi strategies requires better understanding of viral siRNA biogenesis and viral anti-silencing strategies in virus-infected plants.