Global survey of marine RNA viruses sheds light on origins and abundance of Earth’s RNA virome

An extensive evaluation of ocean RNA sequences from waters worldwide has identified thousands of previously unknown RNA viruses – doubling known RNA virus phyla – including some representing a “missing link” in RNA virus evolution. Virtually unknown outside of their role in disease, RNA viruses’ ecological relevance and evolutionary origins are better illuminated through the study’s results. Viruses are ubiquitous in all domains of life and play a critical role as drivers of evolution, biological diversity and global geochemical cycling. Most efforts to understand the myriad functions of Earth’s virome have focused on DNA viruses, which are known to be abundant, diverse and key ecosystem players. Outside of their role as animal and plant pathogens, RNA viruses in the environment are vastly understudied. By analyzing nearly 28 terabases of Global Ocean RNA sequences collected during the Tara Oceans expeditions, Ahmed Zayed and colleagues addressed this knowledge gap and vastly expand the known catalog of marine RNA viruses. In their analysis, Zayed et al. doubled the number of orthornaviran phyla from 5 to 10 (orthornavirans are RNA viruses) and reconstructed a phylogenetic tree that reveals new insights into the evolution of RNA viruses. Among the new phyla, the authors discovered the globally distributed Taraviricota, which represent a missing link for the evolutionary origins of RNA viruses with regard to retroelements, suggesting that the two share a common ancestor. According to the authors, the new findings represent foundational knowledge crucial to further integrating RNA viruses into ecological, evolutionary and epidemiological models. “Studies such as that by Zayed et al. create connections between viral and cellular worlds, allowing for the possibility of a fully integrated tree of life and a more complete understanding of the origins and evolution of all life,” write Jessica Labonté and Kathryn Campbell in a related Perspective.