Systematic evaluation of horizontal gene transfer between eukaryotes and viruses

Gene exchange between viruses and their hosts acts as a key facilitator of horizontal gene transfer and is hypothesized to be a major driver of evolutionary change. Our understanding of this process comes primarily from bacteria and phage co-evolution, but the mode and functional importance of gene transfers between eukaryotes and their viruses remains anecdotal. Here we systematically characterized viral-eukaryotic gene exchange across eukaryotic and viral diversity, identifying thousands of transfers, and revealing their frequency, taxonomic distribution, and projected functions. Eukaryote-derived viral genes, abundant in the Nucleocytoviricota, highlighted common strategies for viral host-manipulation, including metabolic reprogramming, proteolytic degradation, and extracellular modification. Furthermore, viral-derived eukaryotic genes implicate genetic exchange in the early evolution and diversification of eukaryotes, particularly through viral-derived glycosyltransferases, which have impacted structures as diverse as algal cell walls, trypanosome mitochondria, and animal tissues. These findings illuminate the nature of viral-eukaryotic gene exchange and its impact on the evolution of viruses and their eukaryotic hosts.