LAUSR

Whereas DNA viruses are known to be abundant, diverse, and commonly key ecosystem players, RNA viruses are insufficiently studied outside disease settings. In this study, we analyzed ≈28 terabases of Global Ocean RNA sequences to expand Earth’s RNA virus catalogs and their taxonomy, investigate their evolutionary origins, and assess their marine biogeography from pole to pole. Using new approaches to optimize discovery and classification, we identified RNA viruses that necessitate substantive revisions of taxonomy (doubling phyla and adding >50% new classes) and evolutionary understanding. “Species”-rank abundance determination revealed that viruses of the new phyla “Taraviricota,” a missing link in early RNA virus evolution, and “Arctiviricota” are widespread and dominant in the oceans. These efforts provide foundational knowledge critical to integrating RNA viruses into ecological and epidemiological models. Description Expanding the RNA catalog Apart from their roles in human infectious diseases, we understand relatively little about RNA viruses in the wider world. Recently, the discovery curve has been spectacular and has revealed unexpected diversity. Zayed et al. optimized discovery and classification methods on Tara Oceans RNA sequence data to double the roster of known RNA virus phyla (see the Perspective by Labonté and Campbell). This is not just a numbers game; the authors also found a missing link in RNA virus evolution and discovered new phyla that dominate in the oceans and might infect mitochondria. These viruses require an ancient enzyme, RNA-directed RNA polymerase (RdRp) for replication, which is thus used as a marker of deep evolutionary relationships. In addition to the primary sequence data, information on the three-dimensional structures of the RdRp, network-based clusters, other genomic domains, and whole-genome characteristics help reshape the outlines of the evolutionary history of RNA viruses. —CA Viruses of two candidate phyla are abundant in the ocean and revise our understanding of early RNA virus evolution.