Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2005
Publication Date: 12/27/2005
Citation: Webb, B.A., Strand, M.R., Dickey, S.E., Hilgarth, R.S., Beck, M.H., Walter, B.E., Kadash, K., Kroemer, J.A., Lindstrom, K.G., Rattanadechakul, W., Shelby, K., Thoetkiattikul, H., Turnbull, M.W., Whitherell, R.A. 2005. Polydnavirus genomes reflect their dual roles as mutualists and pathogens. Virology. 347:160-174
Interpretive Summary: Polydnaviruses are a family of viruses associated with parasitic wasps that parasitize caterpillar pests. Polydnaviruses cause severe stunting and immune disorders in the parasitized caterpillar. We sequenced and compared the genomes of two polydnaviruses, revealing many novel genes altering pest insect growth, endocrinology and immunity. These novel genes are lead compounds useful to the development of new insect control chemistries by the agrochemical industry, seed companies, and could increase the efficacy of commercial insectary reared parasitoids used by producers for biologically-based pest control.
Technical Abstract: Symbionts often exhibit significant reductions in genome complexity while pathogens often exhibit increased complexity through acquisition and diversification of virulence determinants. A few organisms have evolved complex life cycles in which they interact as symbionts with one host and pathogens with another. How the predicted and opposing influences of symbiosis and pathogenesis affect genome evolution in such instances, however, is unclear. The Polydnaviridae is a family of double-stranded DNA viruses associated with parasitoid wasps that parasitize other insects. Polydnaviruses (PDVs) only replicate in wasps but infect and cause severe disease in parasitized hosts. This disease is essential for survival of the parasitoid's offspring. Thus, a true mutualism exists between PDVs and wasps as viral transmission depends on parasitoid survival and parasitoid survival depends on viral infection of the wasp's host. To investigate how life cycle and ancestry affect PDVs, we compared the genomes of Campoletis sonorensis ichnovirus (CsIV) and Microplitis demolitor bracovirus (MdBV). CsIV and MdBV have no direct common ancestor, yet their encapsidated genomes share several features including segmentation, diversification of virulence genes into families, and the absence of genes required for replication. In contrast, CsIV and MdBV share few genes expressed in parasitized hosts. We conclude that the similar organizational features of PDV genomes reflect their shared life cycle but that PDVs associated with ichneumonid and braconid wasps have likely evolved different strategies to cause disease in the wasp's host and promote parasitoid survival.