Upon oviposition, parasitoid wasps inject their eggs along with venom, teratocytes and polydnavirus (PDV) on the host. Among these parasitic factors, PDVs are known to suppress the host immune system and utilize the host translational mechanisms allowing the juvenile parasitoid to develop. Polydnavirusencoded genes can selectively inhibit host translation and still use the translation machinery of the host to synthesize their own proteins. In this study, we utilize a proteomic approach involving two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) that couples isoelectric focusing (IEF) and SDS-PAGE to resolve complex protein mixtures that results from the parastization of Cotesia plutellae on the lepidopteran host, Plutella xylostella. We specifically analyze the changes in protein synthesis using this technique after treatment of HTIFs that has been previously identified on C. plutellae. The difference in protein profile due to parasitization was confirmed by in vitro translation assay using rabbit reticulosyte lysate.

A cysteine- rich protein encoded by Cotesia plutellae bacovirus (CpBV) was identified in the parasitized Plutella xylostella. The gene, called CpBV-CRP, encodes 189 amino acids with a signal peptide of 20 residues at N-terminus determined by bioinformatic analysis, suggesting a secretory protein. High CpBV-CRP expression in the parasitized P. xylostella was observed at early days after parasitization and decreased with the course of parasitization. Expression of CpBV-CRP was tissue-specific in the fat body/epidermis, but not in hemocyte and gut. Its physiological function was analyzed by transient expression of a CpBV segment containing CpBV-CRP. The treated larvae underwent an immunosuppression in terms of hemocyte-spreading behavior. When the treated larvae were also co-injected with dsRNA against CpBV-CRP, the suppressed hemocyte behavior was significantly recovered. This study reports a cysteine-rich protein encoded in CpBV genome and its physiological function to be an immunosuppressant.