There is now compelling evidence supporting RNA silencing as a novel RNA-based antiviral immunity in insects since RNAi was first demonstrated more than 5 years ago. First, virus infection triggers RNA silencing in insect cells that specifically targets the invading viral RNA. Second, invertebrate viruses such as FHV and NoV encode suppressors of RNA silencing essential for infection of insect cells in which the RNA-silencing pathway is not compromised. It is also clear that the insect RSAR is mediated by the RNAi pathway, which is based mostly on the experimental induction of RNA silencing by exogenous dsRNA. This is because the nodaviral B2 protein suppresses RNA silencing in insect cells induced by either dsRNA or viral RNA replication and the insect RSAR involves Dicer recognition of replicating virus RNAs and is RISC-dependent. The demonstration that RNAi naturally protects insects from virus infection opens up the possibility of using this pathway to control insects that are either crop pests or vectors for crop and human pathogens.
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