RNA interference-mediated antiviral defense in insects

• Insect RNA interference (RNAi) pathways detect and restrict viruses.
• Dicer-2 detects diverse viral dsRNA signatures and initiates the RNAi pathway.
• RNAi may play a role in establishing persistent, non-pathogenic virus infections.
• Both RNA and DNA viruses encode inhibitors of RNAi.
• The RNAi-related piRNA pathway may also restrict virus replication in insects.

Small interfering RNA (siRNA)-mediated RNA interference (RNAi) pathways are critical for the detection and inhibition of RNA virus replication in insects. Recent work has also implicated RNAi pathways in the establishment of persistent virus infections and in the control of DNA virus replication. Accumulating evidence suggests that diverse double-stranded RNAs produced by RNA and DNA viruses can trigger RNAi responses yet many viruses have evolved mechanisms to inhibit RNAi defenses. Therefore, an evolutionary arms race exists between host RNAi pathways and invading viral pathogens. Here we review recent advances in our knowledge of how insect RNAi pathways are elicited upon infection, the strategies used by viruses to counter these defenses, and discuss recent evidence implicating Piwi-interacting RNAs in antiviral defense.