Lenarviricota

Lenarviricota is the first branch of RNA viruses to emerge, since they are the most basal branch.^[1] Most of its members, the leviviruses (class Leviviricetes), only infect prokaryotes, and their known level of diversity has grown dramatically in recent years, which suggests that the RNA viruses may be more widespread in prokaryotes than previously believed.^[3]

It has been suggested that the origin of Lenarviricota may predate that of the last universal common ancestor (LUCA).^[3] Lenarviricota viruses appear to have arisen from a primordial RdRP of the RNA-protein world that gave rise to leviviruses (class Leviviricetes).^[4] It has also been suggested that the retroelements of cellular life (group II introns and retrotransposons) evolved from a shared ancestor with Lenarviricota.^[5]

The eukaryotic RNA viruses without capsids, Mitoviridae, Narnaviridae and Botourmiaviridae, arose from the leviviruses with the loss of the capsid during the time that eukaryogenesis occurred, when the bacterial endosymbiont became the mitochondria. The genus Ourmiavirus arose by recombination between a non-capsid botourmiavirus and a virus from the family Tombusviridae, which inherited its capsid proteins.^[1][4]

The following classes are recognized:^[6]

• Amabiliviricetes
• Howeltoviricetes
• Leviviricetes
• Miaviricetes