38th Annual Meeting of the Society for Invertebrate Pathology

At the time of parasitization, the ichneumonid Tranosema rostrale injects a polydnavirus that assists the wasp egg and larva in subjugating the development and immunity of its host, the spruce budworm (Choristoneura fumiferana). In vitro tests aimed at characterizing this T. rostrale ichnovirus (TrIV) demonstrated that it can infect cells of the Cf-124T cell line, and can express several viral genes. Remarkably, the gene TrFRep1, found on TrIV genome segment F, shows stable expression for at least 100 days after inoculation, compared to a few days for the other viral transcripts examined. We wanted to test the hypothesis that the integration of segment F in the genomic DNA of Cf-124T cells is responsible for the sustained expression. A Southern analysis of DNA isolated from TrIV-inoculated Cf-124T cells showed that episomal copies of segment F disappear four days after TrIV inoculation, while a high-molecular form persists for more than 100 days. This suggested an intimate association between Cf-124T genomic DNA and segment F. The cloning and sequencing of segment F/Cf-124T genomic DNA junction sites, from a lambda genomic library, confirmed that the segment does integrate. Further experiments are under way to determine whether the phenomenon also occurs in vivo.