Segment W of Campoletis sonorensis virus: Expression, gene products, and organization

Campoletis sonorensis virus (CsV, Polydnaviridae) is a segmented double-stranded DNA virus which has an apparently symbiotic relationship with the parasitic wasp, Campoletis sonorensis. CsV replicates in the oviducts of the parasitic wasp and is injected into the wasp's host, Heliothis virescens (Lepidoptera; Noctuiidae), during oviposition. In the parasitized lepidopteran host, the virus has a dramatic effect on host physiology and viral gene products are believed to play an essential role in the survival of the parasitic wasp's egg and larva. In the current study, we used Northern blot analyses to examine expression from segment W in the parasitized host and in the parasitic wasp. Segment W hybridized primarily to two relatively abundant mRNAs (1.6 and 1.0 kb) from the parasitized host. These 1.6- and 1.0-kb mRNAs, which were previously shown to be transcribed from two closely related genes (WHv1 and WHv2) on segment W ( G. W. Blissard, O. P Smith, and M. D. Summers, 1987, Virology 160,120–134 ) increased in relative abundance between 2 and 24 hr postparasitization (pp) and were detected throughout parasitization (8 days). To study the proteins encoded by these closely related genes, the open reading frame from each of the related genes was cloned into a baculovirus expression vector. By pulse labeling in the presence and absence of tunicamycin, we examined secretion and glycosylation of these CsV proteins in infected lepidopteran cells ( Spodoptera frugiperda). Expression of segment W in the oviducts of the female wasp was also examined. Segment W hybridized to at least five CsV mRNAs on Northern blots of poly(A) mRNA from C. sonorensis oviducts. To identify specific CsV mRNAs and map putative viral genes expressed in wasp oviduct tissues, segment W was used to screen a cDNA library of C. sonorensis oviduct mRNAs. Three cDNAs were used to identify CsV mRNAs by Northern blot analyses and to map the locations of three putative CsV genes on segment W. Cross-hybridization within the CsV genome was examined with cloned segment W and with the three cloned cDNAs.