Interesting paper on a sort of bird’s eye view of virus evolution across the history of life, and an attempt to come up with a system of viral taxonomy encompassing all viruses.
The Ultimate Network Architecture of the Virus World
The final question that we must address here is whether evolutionary connections across the entire virus world exist that would make the megataxon “Viruses” a legitimate concept. As discussed above, some major groups of viruses, for example, the two realms of dsDNA viruses, do not share an ancestry. Yet the matter is not unambiguous. Indeed, three simple protein domains that are present in multiple (super-)VHGs, namely, (i) the RNA recognition motif (RRM) that forms the cores of all virus polymerases; (ii) the jelly roll, the core domain of SJR- and DJR-MCPs; and (iii) S3H, the replicative helicase of diverse viruses, link the majority of the viruses in all BCs and in three of the four proposed realms (Fig. 12) (80). Thus, underneath the vastly different evolutionary histories and the polyphyly of viruses, fundamental structural and evolutionary unity likely harkens back to the primordial pool of genetic elements. In particular, primordial RNA replicons, including reverse-transcribing replicons akin to extant group II introns, were the likely ancestors of the realm Riboviria (80).