Résumé
Polydnaviruses (PDVs) are symbiotic double-stranded DNA viruses produced in the reproductive organs of hymenopteran endoparasitoids and transmitted to their lepidopteran hosts during oviposition. Expression of viral genes in host infected cells and tissues leads to immunosuppression, a condition required for the survival of parasitoids. Recent genomic studies revealed that viral genes are clustered in multigene families in the packaged genome of PDVs. The viral ankyrin family is present in all sequenced PDV genomes. We identified nine vankyrin genes in the genome of the Hyposoter didymator ichnovirus (HdIV), the PDV associated with the endoparasitic wasp H. didymator (Hymenoptera: Ichneumonidae). H. didymator parasitizes several noctuid species, in particular Spodoptera spp. Time course gene expression experiments indicate that all HdIV vankyrins are detected at moderate and relatively constant level throughout parasitism of S. frugiperda larvae. To find out more on tissue and/or species specificity transcriptions, the expression profiles of HdIV vankyrin genes were compared between S. frugiperda and S. littoralis larvae and in different insect cell lines. Our results showed that, among all vankyrin members, Hd27-vank1 exhibits a highest expression level specifically in all tissues of larvae and cell lines of Spodoptera species. In contrast, a differential expression pattern and level of HdIV vankyrins were observed in two insect cell lines not related to Spodoptera species. These results suggest that Hd27-vank1 have pleiotropic functions during parasitism of Spodoptera spp, and more generally, that divergence in vankyrin gene expression may be related to variation in host specificity.