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/2017/04/30/132399.short 4100 - http://biorxiv.org/content/early/2017/04/30/132399.full AB - Bracoviruses (BVs) and Ichnoviruses (IVs) belong to the family Polydnaviridae (PDV), which associates symbiotically with parasitoid wasps, working as vectors of virulence genes, and allowing the development of wasp larvae within hosts. One of the viral segments (c35) of Cotesia vestalis bracovirus (CvBV) contains an ORF that has been previously described as a helicase of unknown origin. Here we demonstrate that this gene is a Rep/Helicase from an autonomous Helitron transposable element (TE), which covers the viral segment almost entirely. This description of a PDV-Helitron fusion points to a new type of relationship between TEs and viruses. Our results also suggest that this TE underwent two consecutive horizontal transfer (HT) events: first from a Drosophila host ancestor to the genome of C. vestalis and its BV (CvBV), and then from C. vestalis to a lepidopteran host (Bombyx mori); the latter probably facilitated by viral segments injected during parasitization. We discuss this Helitron–BV fusion, the apparent TE exaptation by a PDV and its function, and implications for the study of wasp–host interaction and evolution.