Abstract
BackgroundThe abundance and the conservation of the repeated element (rep) genes in Ichnoviruses genomes suggest that this gene family plays an important role in viral cycles. In the Ichnovirus associated with the wasp Hyposoter didymator, named HdIV, 10 rep genes were identified to date. In this work, we report a relative quantitative transcription study of these HdIV rep genes in several tissues of the lepidopteran host Spodoptera frugiperda as well as in the H. didymator wasps.ResultsThe data obtained in this work indicate that, in the early phases of infection (24 hours), HdIV rep genes each display different levels of transcripts in parasitized 2nd instar or HdIV-injected last instar S. frugiperda larvae. Only one, rep1, is significantly transcribed in female wasps. Transcript levels of the HdIV rep genes were found as not correlated to their copy number in HdIV genome. Our results also show that HdIV rep genes display different tissue specificity, and that they are primarily transcribed in S. frugiperda fat body and cuticular epithelium.ConclusionThis work is the first quantitative analysis of transcription of the ichnovirus rep gene family, and the first investigation on a correlation between transcript levels and gene copy numbers in Ichnoviruses. Our data indicate that, despite similar gene copy numbers, not all the members of this gene family are significantly transcribed 24 hours after infection in lepidopteran larvae. Additionally, our data show that, as opposed to other described HdIV genes, rep genes are little transcribed in hemocytes, thus suggesting that they are not directly associated with the disruption of the immune response but rather involved in other physiological alterations of the infected lepidopteran larva.
Highlights
The abundance and the conservation of the repeated element genes in Ichnoviruses genomes suggest that this gene family plays an important role in viral cycles
30 members of the rep gene family have been reported in the fully sequenced Campoletis sonorensis IV (CsIV) genome, whereas 36 and ten rep genes are described in Hyposoter fugitivus IV (HfIV) and Tranosema rostrale IV (TrIV), respectively [7]
The rep6 probe hybridized with two Hyposoter didymator IchnoVirus (HdIV) segments, firstly with a segment that co-localizes with the rep5 segment and secondly with another segment of lower size (Figure 1, rep6 lane)
Summary
The abundance and the conservation of the repeated element (rep) genes in Ichnoviruses genomes suggest that this gene family plays an important role in viral cycles. In the Ichnovirus associated with the wasp Hyposoter didymator, named HdIV, 10 rep genes were identified to date. Recent sequencing programs of the polydispersed polydnavirus genomes reveal that a large proportion of the genes encoded by the circular DNA molecules are organized in gene families. This characteristic is common to the two polydnavirus families, the Ichnoviruses (IV), associated with ichneumonid wasps, and the Bracoviruses (BV), associated with braconid wasps [6,7]. We are studying the Ichnovirus associated with the endoparasitoid wasp Hyposoter didymator (HdIV), where several gene families have been identified so far [7,8]. 30 members of the rep gene family have been reported in the fully sequenced CsIV genome, whereas 36 and ten rep genes are described in Hyposoter fugitivus IV (HfIV) and Tranosema rostrale IV (TrIV), respectively [7]
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