The origins and evolution of the RNA virome in land flora.

The colonization of land by plants was a major transition in the history of life, fundamentally reshaping the evolution of terrestrial organisms and Earth's ecosystems. Plants are hosts to an enormous diversity of viruses, but the origins and evolution of these viruses are not thoroughly understood. In this study, we mined the transcriptomes and genomes of 2402 species sampled across the plant kingdom and discovered about 35 000 plant-associated RNA viruses, including several potential families not described previously, resulting in a 2.2-fold increase in the known plant-associated RNA virus diversity, greatly expanding the virus host ranges, and revealing many groups of atypical, apparently persistent viruses. Phylogenetic analysis shows that plant viruses emerged on numerous independent occasions, mostly via horizontal virus transfer facilitated by close ecological associations of plants with other terrestrial organisms, such as invertebrates and fungi. Collectively, our work substantially expands the known diversity of plant RNA viruses, provides a major resource for studying plant RNA virome, and contributes to understanding the origins and natural history of plant RNA viruses.