Abstract
Sequences derived from a novel toursvirus were identified from pooled genomic short read data from U.S. populations of southern corn rootworm (SCR, Diabrotica undecimpunctata howardi Barber) and northern corn rootworm (NCR, Diabrotica barberi Smith & Lawrence). Most viral sequences were identified from the SCR genomic dataset. As proteins encoded by toursvirus sequences from SCR and NCR were almost identical, the contig sets from SCR and NCR were combined to generate 26 contigs. A total of 108,176 bp were assembled from these contigs, with 120 putative toursviral ORFs identified indicating that most of the viral genome had been recovered. These ORFs included all 40 genes that are common to members of the Ascoviridae. Two genes typically present in Ascoviridae (ATP binding cassette transport system permeases and Baculovirus repeated open reading frame), were not detected. There was evidence for transposon insertion in viral sequences at different sites in the two host species. Phylogenetic analyses based on a concatenated set of 45 translated protein sequences clustered toursviruses into a distinct clade. Based on the combined evidence, we propose taxonomic separation of toursviruses from Ascoviridae.
Highlights
A complex of four corn rootworm species and subspecies are native to North America; western corn rootworm (WCR), Diabrotica virgifera virgifera (LeConte), southern corn rootworm (SCR), Diabrotica undecimpunctata howardi (Barber), Mexican corn rootworm, Diabrotica virgifera zeae (Krysan & Smith), and northern corn rootworm (NCR), Diabrotica barberi (Smith & Lawrence) [1]
Novel Toursvirus-like Sequences Identified from SCR and NCR
Fragments, ranging from 469–19,547 bp from the SCR assembly showed significant identity with toursviruses. These putative novel toursvirus-like DNA fragments predicted a cumulative total of 115 protein coding sequences (CDS ≥ 50 aa)
Summary
A complex of four corn rootworm species and subspecies are native to North America; western corn rootworm (WCR), Diabrotica virgifera virgifera (LeConte), southern corn rootworm (SCR), Diabrotica undecimpunctata howardi (Barber), Mexican corn rootworm, Diabrotica virgifera zeae (Krysan & Smith), and northern corn rootworm (NCR), Diabrotica barberi (Smith & Lawrence) [1]. Ascoviruses in the genus Ascovirus primarily infect lepidopteran larvae in the family Noctuidae and are vectored during oviposition by parasitoid wasps For their potential use as biocontrol agents, ascoviruses cause chronic and fatal disease in their larval lepidopteran hosts [28]. To assess the potential for virus-based suppression of Diabrotica spp., we examined the associated virome drawing on both genomic and transcriptomic sequence data [30] From this we found evidence for a diverse set of corn rootworm viruses. We report a novel toursvirus, with the genome sequence assembled from short sequence reads derived from both SCR and NCR DNA extracts This is the first putative member of Ascoviridae isolated from Coleoptera
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