Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 24, 2002
Publication Date: N/A
Interpretive Summary: Polydnaviruses are symbiotic viruses of parasitic wasps and are injected along with eggs by parasitic wasps into host larvae during oviposition. Inside the host larva, polydnavirus genes are expressed and the gene products function to impair the host defense response to ensure the successful development of the wasp. In the present study, one polydnavirus sgene was identified, by molecular methods, to be expressed in gypsy moth larvae which were hosts of the parasitic wasp. The expression of this viral gene could be detected in the host as early as two hours and continued for eight days after it was parasitized. Further, the viral gene expression was detected in the tissues of the host blood, brain, and fat body. The highest level of expression was seen in the blood. Moderate expression was observed in the brain and the weakest expression was observed in the fat body of the host. The early occurrence of the viral gene expression and highest viral gene expression seen in the blood sugges that this viral gene may be involved in the disruption of host defense response and protection of parasitic eggs from the host. These findings are expected to help researcher better understand the process by which certain insect parasites, many of which are important biological agents, successfully parasitize their hosts.
Technical Abstract: Glyptapanteles indiensis is a polydnavirus-carrying wasp that parasitizes the larval stage of the gypsy moth, Lymantria dispar, where it injects its eggs along with the polydnavirus (GiPDV). Within host tissues, GiPDVs do not replicate, but viral genes are expressed that function to suppress the host's immune response and to ensure successful parasitism. Recently, one of the GiPDV circular genome segments associated with integration, p157, was sequenced and an associated functional protein tyrosine phosphatase (PTP) gene (PDVPTP) was identified and expressed (Gundersen-Rindal & Chen, submitted). In the present study, we monitored the in vivo expression of PDVPTP in the parasitized L. dispar host using one step RT-PCR and evaluated the expression levels of PDVPTP transcript in various host tissues using RT quantitative competitive PCR ( RT-qcPCR). Transcription of PDVPTP could be detected in the host as early as 2 hours post parasitization (pp) and continued for 8 days pp. Viral PDVPTP was expressed in the tissues of the larval host hemolymph, brain, and fat body; although the expression levels in each tested tissue varied. The highest level of PDVPTP expression was seen in hemolymph. Moderate expression was observed in the brain and weakest expression was observed in fat body of the host. The highest expression level in the host hemolymph together with the fact that abundant expression of PDVPTP gene occurred at early stage of parasitizaiton (2 h pp) suggests that the viral PTP may be involved in the disruption of the host immune system and protection of endoparasitoid egg from encapsulation. This is the first report of quantitative profiles of polydnavirus gene expression in its natural host tissues.