RESUMO
Bracoviruses associate symbiotically with thousands of parasitoid wasp species in the family Braconidae, working as virulence gene vectors, and allowing the development of wasp larvae within hosts. These viruses are composed of multiple DNA circles that are packaged into infective particles, and injected together with wasp's eggs during parasitization. One of the viral segments of Cotesia vestalis bracovirus contains a gene that has been previously described as a helicase of unknown origin. Here, we demonstrate that this gene is a Rep/Helicase from an intact Helitron transposable element that covers the viral segment almost entirely. We also provide evidence that this element underwent at least two horizontal transfers, which appear to have occurred consecutively: first from a Drosophila host ancestor to the genome of the parasitoid wasp C. vestalis and its bracovirus, and then from C. vestalis to a lepidopteran host (Bombyx mori). Our results reinforce the idea of parasitoid wasps as frequent agents of horizontal transfers in eukaryotes. Additionally, this Helitron-bracovirus segment is the first example of a transposable element that effectively became a whole viral circle.
Assuntos
Transferência Genética Horizontal/genética , Himenópteros/genética , Insetos Vetores/genética , Polydnaviridae/genética , Animais , Bombyx/genética , Bombyx/parasitologia , DNA Helicases/genética , Elementos de DNA Transponíveis/genética , Drosophila/genética , Drosophila/parasitologia , Genoma Viral/genética , Himenópteros/virologia , Insetos Vetores/virologiaRESUMO
The diversity of symbionts associated with insects and the range of effects they exert on their hosts haveprompted studies to understand the role these microorganisms may have on host biology, particularly inrelation to the interaction of their hosts with other trophic levels. There is also a possibility of using suchsymbionts as vectors of genes for insect control or learning on the mechanisms they use to interact with theirhosts for the development of new approaches to insect control. Since most of these symbionts are transmittedtransovarially from one generation to another, we used electron microscopy to assess the occurrence andmorphology of these microorganisms in the female reproductive tissues of two important insect pestparasitoids, the braconids Cotesia flavipes and Doryctobracon areolatus. Cotesia flavipes was associatedwith a polydnavirus (PDV), whereas D. areolatus harbored the rickettsia-like bacterium Wolbachia. Theultrastructural morphology and localization of these symbionts in their host ovaries are described. None ofthe populations of the species studied were associated with non-PDV particles, and their sole associationwith specific symbionts will facilitate studies on the role of these symbionts in the association with theirhosts, and on the associations of their hosts with other trophic levels.