Submitted to: Genome Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/30/2008
Publication Date: 12/30/2008
Citation: Desjardins, C. A., Gundersen-Rindal, D.E., Hostetler, J.B., Tallon, L.J., Fadrosh, D.W., Fuester, R.W., Pedroni, M.J., Haas, B.J., Schatz, M.C., Jones, K.M., Crabtree, J., Forberger, H., Nene, V. 2008. Comparative genomics of mutualistic viruses of Glyptapanteles parasitic wasps. Genome Biology. 9:R193. Interpretive Summary: Tiny wasps known as parasitoids have potential to control moth pests, such as caterpillars, of agricultural crops and forests. The survival of many of these wasps is enhanced by a virus, called a polydnavirus, that is injected along with the wasp egg into a host caterpillar pest. In this study we use modern molecular techniques to sequence and characterize the two different forms of the virus: (1) the free form of the virus that is injected into the caterpillar by the wasp and (2) the provirus form that is a part of the wasp DNA before it is removed to become the free virus. This study represents the most comprehensive study ever made of the provirus form, and many new discoveries were made. The information obtained will help explain how the polydnavirus may be formed and replicate, how the virus may help the wasp to survive, and may lead to new biocontrol strategies. This information will be of interest to university and industry scientists who are interested in virus evolution and/or in developing new virus-based strategies to control pests.
Technical Abstract: Polydnaviruses, a family of double-stranded DNA viruses with segmented genomes, have evolved as obligate endosymbionts of endoparasitoid wasps, and are some of the few viruses known to share mutualistic relationships with eukaryotic hosts. Virus particles are replication deficient and are produced only by female wasps from proviral sequences integrated in the wasp genome. Virus particles are subsequently co-injected with eggs into lepidopteran hosts, where viral gene expression facilitates parasitoid survival and therefore survival of proviral DNA. Here, we report the full genome sequence of the braconid Glyptapanteles indiensis and Glyptapanteles flavicoxis wasp encapsidated viral genomes (GiBV and GfBV, respectively) in their entirety, as well as their nearly complete proviral genomes. GiBV and GfBV genomes each comprise 29 double-stranded DNA segments of varying sizes. Sequences for 25/29 and 28/29 viral genome segments for GiBV and GfBV, respectively, were obtained through whole genome shotgun sequencing, while the remaining 4 and 1 genome segments, respectively, required reciprocal illumination from the proviral genomes. GiBV and GfBV were each discovered to encode a gene family of sugar transporters which has not been found in other sequenced polydnaviruses. Examination of Gi and Gf nearly complete proviral genome sequences confirmed the hypothesis that Bracovirus proviral segments are not all tandemly arrayed. Synteny between GiBV and GfBV proviral genome sequences suggested ~70% of viral genome segments (21/29) are clustered in an array of 21 segments within a stretch of ~600 kbp. These arrays are separated by non-segment DNA encoding 2 genes which resemble wasp proteins. The remaining 5 GiBV and GfBV proviral loci contain either 1 or 2 proviral segments and all flanked by large stretches of non-segment DNA which also code for wasp proteins. Our data support the concept of a macrolocus within a parasitoid chromosome as a single origin for the proviral form, raise several interesting evolutionary hypotheses, and redefine the extant of the polydnavirus genome.