Origins and Evolution of the Global RNA Virome

Yuri I. Wolf; Darius Kazlauskas; Jaime Iranzo; Adriana LucÍa-Sanz; Jens H. Kuhn; Mart Krupovic; Valerian V. Dolja; Eugene V. Koonin

The reconstruction of protein gain-loss, together with the comparison of genome 376 architectures in this branch, reveal extensive rearrangements as well as gene and module 377 displacement ( Figure 3B and S2B). Branch 2 includes viruses with relatively long genomes and 378 complex gene repertoires (nidoviruses, potyviruses and many members of Picornavirales) along 379 with viruses with much shorter genomes and minimal sets of genes (astroviruses and 380 solemoviruses). Clearly, evolution of Branch 2 viruses involved multiple gene gains. Of special 381 note is the gain of 3 distinct helicases in 3 clades within this branch: superfamily 3 helicases 382 (S3H) in members of Picornavirales, superfamily 2 helicases (S2H) in potyviruses, and 383 superfamily 1 helicases (S1H) in nidoviruses ( Figure 3B and S2B). This independent, convergent 384 gain of distinct helicases reflects the trend noticed early in the study of RNA virus evolution, 385 namely, that most viruses with genomes longer than ~6 kb encode helicases, whereas smaller 386 ones do not. This difference conceivably exists because helicase activity is required for the 387 replication of longer RNA genomes (73). Another notable feature is the change of virion 388 All rights reserved. No reuse allowed without permission.