Viruses as vectors of horizontal transfer of genetic material in eukaryotes

Horizontal transfer (HT) of genetic material, mainly transposable elements, is increasingly recognized as an important factor shaping eukaryote genomes. Yet our understanding of the mechanisms and vectors underpinning these transfers is still limited. It has been proposed that such transfers may be facilitated by viruses, because they typically inject their genomes into host cells to replicate and they can be horizontally transmitted between their hosts. Recent evidence from high throughput sequencing of viral populations and paleovirology shows that both virus-to-host and host-to-virus gene flow can be common in a variety of eukaryote lineages. We argue that such studies reinforce the hypothesis of viruses as major vectors of HT in eukaryotes.