Identification of bracovirus particle proteins and analysis of their transcript levels at the stage of virion formation

Abstract

Polydnaviruses (PDVs) are unique symbiotic viruses associated with parasitic wasps; they replicate only in the calyx cells of a wasp's ovaries and are transferred at oviposition along with the parasitoid egg into the lepidopteran host. The DNA packaged in the viral particles encodes factors that manipulate the host's immune defences and development to benefit the parasitoid. PDVs are found in two subfamilies of ichneumonids (ichnoviruses) and in braconids of the microgastroid complex (bracoviruses). We recently showed that the latter derive from an ancestral nudivirus, as 24 nudivirus-related genes were identified in ovaries of two distantly related braconids at the stage of virion formation. Here, we present a comprehensive analysis of the viral particle proteins of the Chelonus inanitus bracovirus (CiBV). Proteins of purified CiBV particles were analysed by mass spectrometry and amino acid sequences matched to the existing ovarian-cDNA database. In addition, transcript quantities of identified genes were measured by quantitative real-time PCR in female pupae at the onset and peak of virion formation and at corresponding stages in male pupae. This combined approach allowed the identification of 44 CiBV particle proteins: 16 were nudivirus-related, three had similarity to ovarian proteins of another braconid, 11 had similarity to cellular proteins and 14 had no similarity to known proteins. The transcripts of all of them increased in female, but not male, pupae. These data confirm the important contribution of nudivirus genes but also indicate the presence of many lineage-or species-specific proteins possibly involved in the parasitoid-host interaction.

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

“…Analyses of these regions in Glyptapanteles and Cotesia spp. revealed that the odv-e66-like1 nudiviral gene encoding a bracovirus particle component [8] was localized between PL1 and PL2 within the macrolocus (figures 1 and 2). For C. congregata, this region was obtained by sequencing overlapping fragments isolated by PCR with primers designed based on conserved Glyptapanteles and C. sesamiae genes (figure 2 and table 1; electronic supplementary material, S5).…”

“…This EVE corresponds to the major remnant of the nudivirus genome captured by the wasp ancestor [4,6,7], whereas other nudiviral genes have been dispersed in the wasp genome. Nudiviral genes encode the viral RNA polymerase, BV particle structural components and envelope proteins [6,8,9]. However, they are not packaged in BV particles, which instead contain multiple dsDNA circular molecules, called 'circles'.…”

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

“…The region is characterized by high gene density and contains intronless genes. This cluster encodes VP39 and 38K, the most abundant proteins in CiBV particles [28] and is amplified during CcBV virus particle production [36]. Other nudiviral genes are now dispersed in the C. congregata genome [10].…”

“…A series of 29 nudivirus genes (nudiviruses are large dsDNA insect viruses related to baculoviruses) were expressed in the ovaries (table 1). Furthermore, one-third of these genes encoded BV particle components [10,27,28]. Last, 18 of these nudiviral genes, corresponding to baculovirus core genes [29], should perform essential functions of the virus cycle, based on functional characterization in baculoviruses [30] (table 1).…”

Paleozoic origin of insect large dsDNA viruses

“…Parasitoid wasps have domesticated these viruses for transferring virulence genes (21)(22)(23), interfering with the immune response and development of their lepidopteran hosts (24,25). The longdebated genuine viral nature of bracoviruses has recently been demonstrated with the discovery in wasp genomes of genes involved in bracovirus particle production (26)(27)(28). These genes, related to nudivirus and baculovirus core genes (27), establish a bridge between the phylogeny of free dsDNA viruses and geologic animal fossil data, thus allowing the exploration of deep evolutionary timescales.…”