PT - JOURNAL ARTICLE AU - Pedro Heringer AU - Guilherme B. Dias AU - Gustavo C. S. Kuhn TI - A horizontally transferred autonomous Helitron became a full polydnavirus segment in <em>Cotesia vestalis</em> AID - 10.1101/132399 DP - 2017 Jan 01 TA - bioRxiv PG - 132399 4099 - http://biorxiv.org/content/early/2017/10/16/132399.short 4100 - http://biorxiv.org/content/early/2017/10/16/132399.full AB - 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 by 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 Cotesia 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.