Involvement of small RNAs in Microplitis demolitor Bracovirus replication

Polydnaviruses are beneficial symbionts of parasitic wasps that are essential for the successful parasitism of insect hosts due to their role in delivery and expression of host immune suppression genes. These viruses share an ancestor with potent insect pathogens, but after 100 million years of association with parasitoid wasps, they have been domesticated and only initiate replication in female wasp ovaries at a precise point in development. Our transcriptome sequencing of wasp ovaries identified several viral genes homologous to those from related nudiviruses and baculoviruses. Using RNAi, we have performed functional experiments examining the roles of viral and host genes in the maintenance of symbiosis, and adaptations that have occurred to generate this unique gene delivery system. Our recent results suggest that miRNAs play a key role in tightly regulating virus replication. Dual analysis of small RNAs and transcript levels on a genome-wide scale has identified several genes with potential roles in activation of virus genes. This work highlights polydnaviruses as a fascinating example of the adaptations that can occur during beneficial symbiosis of a virus with an insect host.