Polydnaviruses (PDVs) are a group of insect viruses and symbiotic to some endoparasitoid wasps classified in to Braconidae and Ichneumonidae. Though a lot of PDV genes are identified and analyzed in the host-parasitoid molecular interactions, PDV replication is still far from our understanding. PDVs are replicated in the wasp ovary during late pupal stage. A PDV, Cotesia plutellae bracovirus (CpBV), is symbiotic to Cotesia plutellae. The C. Plutellae ovary was analyzed in transcriptome by 454 pyrosequencing. The ovarian transcriptome provided several major DNA polymerases including Pol α, Pol δ, and Pol ε. All contigs matched to these polymerases were expressed in C. plutellae. Especially DP1 contig homologous to Pol α was highly expressed during late pupal and female adult stages. Its RNA interference significantly suppressed CpBV viral titre in the ovary. This study suggests a hint that CpBV replication uses a host DNA polymerase, in which Pol α may play a specific role in the viral replication in the ovary.

polydnavirus, Cotesia plutellae bracovirus (CpBV), is symbiotic to an endoparasitoid wasp, C. plutellae, which specifically parasitizes young larvae of the diamondback moth, Plutella xylostella. CpBV contains some genes originated from other insect viruses. CpBV-E94k1 and CpBV-E94k2 are homologous to corresponding baculovirus gene E94k, and may play an important role in host-parasitoid interactions. This study was conducted to confirm the origin and function of CpBV-E94k by analyzing its sequence and functional assays. Our phylogenetic analysis indicates that CpBV acquires these E94k genes from baculoviruses. These two genes were expressed during entire period parasitization period. Expression of these E94ks was also tissue-specific because they were expressed in the hemocyte and fat body, but not in the other tissues. Subsequent analysis of gene function by RNA interference showed that it clearly inhibited host immune and developmental processes

An endoparasitoid wasp, Cotesia plutellae parasitized young larval of diamondback moth, Plutella xylostella. Parasitized larva exhibit significant immunosuppression and fail to metamorphose to pupal stage. Especially, during last instar of parasitized P. xylostella, massive nutrients divert from host to wasp development. HTIF (host translation inhibitory factor) encoded in C. Plutella bracovirus (CpBV) play a crucial role in suppressing host usage of amino acids. However, its inhibitory activity is selective by discriminating mRNAs based on their 5’UTR secondary structures. Our RT-PCR and proteomic analysis indicated that arginine kinase mRNA was inhibited by HTIF, but imaginal disc growth factor was not. Arginine kinase and IDGF were persistently expressed in parasitized P. .xylotella with the gradual decrease at the late parasitisation period. Expression of arginine kinase and IDGF were also tissue specific in the gut/epidermis and haemocyte but not in fat bodies. Subsequent analysis of these gene functions by RNA interference explained the benefit of parasitoid for the mRNA discrimination by HTIF.