A phylogenomic data-driven exploration of viral origins and evolution

Nasir, Arshan; Caetano-Anollés, Gustavo

The uToL supports a polyphyletic origin for viruses. At least two kinds of virions (spherical and filamentous), both apparently unrelated, were the likely precursors of many complex virion morphotypes (Fig. 7A) . The viral mode of life therefore originated more than once in evolution but always before the divergence of modern cells from a cellular stem line of descent. In turn, the support for a monophyletic origin is weak but could be explained by reductive evolution, which is expected to confound the evolutionary patterns, especially if a long time has passed. The seven-set Venn diagram revealed a highly patchy distribution of FSFs in the viral supergroup. Although no FSF was shared by all seven viral subgroups, some ancient FSFs were shared by four to six viral subgroups including mostly RNA viruses. The data also identified a large core of abe FSFs that were shared by viruses infecting the three superkingdoms. Together, the most parsimonious explanation for structural data confirms an ancient cellular history of viruses and their origin from one or more virocell ancestors.