Comparative genomics of mutualistic viruses of Glyptapantelesparasitic wasps

Abstract

Background: Polydnaviruses, double-stranded DNA viruses with segmented genomes, have evolved as obligate endosymbionts of parasitoid wasps. Virus particles are replication deficient and produced by female wasps from proviral sequences integrated into the wasp genome. These particles are co-injected with eggs into caterpillar hosts, where viral gene expression facilitates parasitoid survival and, thereby, survival of proviral DNA. Here we characterize and compare the encapsidated viral genome sequences of bracoviruses in the family Polydnaviridae associated with Glyptapanteles gypsy moth parasitoids, along with near complete proviral sequences from which both viral genomes are derived.

Functional endogenous viral elements in the genome of the parasitoid wasp Cotesia congregata : insights into the evolutionary dynamics of bracoviruses

“…A large majority of proviral segments (75% corresponding to 21 segments) were indeed located in a single region within the wasp genome constituting the so-called macrolocus. However, contrary to the prediction, seven segments were dispersed in five localizations (designated as dispersed loci) [16]. Moreover, although proviral segments and nudiviral genes are believed to originate from the ancestral nudivirus genome, no physical link could be identified between them at the time.…”

When parasitic wasps hijacked viruses: genomic and functional evolution of polydnaviruses

“…This divergence could be explained by the time (100 Myr) elapsed since integration in BV genomes but could also reflect high selection pressures imposed by the interaction with the lepidopteran host [60,63,64] (see §4). However, phylogenetic analyses of the sugar transporter gene family recently acquired by Glyptapanteles BVs showed the BV genes were more closely related to hymenopteran than lepidopteran genes [37]. To date, this represents the only robust example of gene transfer from wasps to PDVs.…”

“…In C. congregata, the proviral segment organization consists of a macrolocus comprising two-third of proviral sequences and seven dispersed loci each with one to three segments (see [15]). Comparisons between Cotesia and Glyptapanteles species [37], which diverged approximately 17 Ma [7], highlighted the homology and the remarkable genomic stability of the proviral integration sites, as orthologous hymenopteran genes were found in the flanking regions (see [15] …”

“…However, comparative genomics on the Glyptapanteles and Cotesia genera revealed a surprising conservation in the localization of most proviral segments, which have remained stably integrated in braconid wasp genomes [15] since the separation of the wasps 17 Ma [7]. Proviral sequences were also subjected to specific gene transfers [37] and duplications [15] leading to unique PDV genome organizations in each wasp species.…”

“…Like any eukaryotic genome, during over 100 Myr of evolution, proviral BVs have been largely exposed to mobile elements, many of which are now rearranged and no longer active. The recently described Maverick TEs were identified in parasitoid wasp genomes, and both in flanking wasp sequences next to GfBV proviral locus and within encapsidated CcBV sequences [37,42]. Functional Mavericks encode a retroviral-like integrase, and a number of proteins with homology to replication and packaging proteins of dsDNA viruses [67].…”