Webb 9603504 Polydnavirus genomes and life cycles are complex. Campoletis somnorensis (PDV) has at least 28 DNA segments with genome size estimates in excess of 250 kb, of which the most abundantly expressed are nested. There is little understanding of the evolutionary pressures that have driven or allowed segmentation of the viral genome. PDVs are obligate symbionts of some parasitic hymenoptera and replicate asymptotically from integrated proviral DNA only in specialized calyx cells of the female reproductive tract. When the wasp paristizes the lepidopteran host, the virus genome invades the host, ceases replicating and viral genes are rapidly expressed at a constant level producing infection. Such viral gene expression is required for successful development of the endoparasitic wasp. The hypothesis that PDV genome segmentation has resulted from selective pressure for high level gene expression in parasitized insects will be tested by cloning and mapping genes on nested viral DNA segments, by evaluating a number of viral structural proteins and by manipulating the level of viral gene expression in host insects. The results of these studies will produce the first comprehensive characterization of a polydnavirus genome allowing critical evaluation of the linkage between segment nesting and levels of gene expression and may produce fundamental insights into the evolutionary forces that have shaped the genomes of polydnaviruses, the only group of segmented DNA viruses.
