Expression of Cotesia kariyai polydnavirus genes in lepidopteran hemocytes and Sf9 cells

The parasitic wasp Cotesia kariyai carries polydnavirus (CkPDV) which is an indispensable factor for the successful parasitization by the wasp. One of its surface proteins has been identified as an immunoevasive mediator from the cellular defense reactions of the host armyworm Pseudaletia separata, thereby it was named immunoevasive protein (IEP). In the present study, we demonstrated that anti-IEP antibody did not suppress the CkPDV infection of Sf9 cells but decreased its infection of P.separata hemocytes, thus indicating that IEP is not essential for CkPDV to enter into the target cells but is important for evading from the attack of the hemocytes. Three genes of CkPDV expressed in Sf9 cells were isolated and characterized. Two of them (CkV0.8, CkV0.9) are novel genes but another one (CkV2.0) is the same gene with the one we previously identified in the parasitized armyworm larvae. Although these genes reside in different DNA segments of CkPDV genome, all of them are expressed in the hemocytes of the parasitized armyworm larvae. These gene transcripts are first detected at 2 h after parasitization, and the expressions of CkV0.8 and CkV0.9 were gradually decreased after reaching the maximum level at 4 h after parasitization. However, the expression of CkV2.0 continues to be increased at least for 10 h after parasitization.