Moreira David, López-García Purificación
Unité d'Ecologie, Systématique et Evolution, CNRS UMR 8079, Université Paris-Sud, Orsay, France
Philos Trans R Soc Lond B Biol Sci. 2015 Sep 26;370(1678):20140327. doi: 10.1098/rstb.2014.0327.
The recent discovery of diverse very large viruses, such as the mimivirus, has fostered a profusion of hypotheses positing that these viruses define a new domain of life together with the three cellular ones (Archaea, Bacteria and Eucarya). It has also been speculated that they have played a key role in the origin of eukaryotes as donors of important genes or even as the structures at the origin of the nucleus. Thanks to the increasing availability of genome sequences for these giant viruses, those hypotheses are amenable to testing via comparative genomic and phylogenetic analyses. This task is made very difficult by the high evolutionary rate of viruses, which induces phylogenetic artefacts, such as long branch attraction, when inadequate methods are applied. It can be demonstrated that phylogenetic trees supporting viruses as a fourth domain of life are artefactual. In most cases, the presence of homologues of cellular genes in viruses is best explained by recurrent horizontal gene transfer from cellular hosts to their infecting viruses and not the opposite. Today, there is no solid evidence for the existence of a viral domain of life or for a significant implication of viruses in the origin of the cellular domains.
最近发现的多种巨型病毒，如米米病毒，催生了大量假说，认为这些病毒与三个细胞域（古菌、细菌和真核生物）共同定义了一个新的生命域。也有人推测，它们在真核生物的起源中发挥了关键作用，作为重要基因的供体，甚至作为细胞核起源时的结构。由于这些巨型病毒的基因组序列越来越容易获得，这些假说可以通过比较基因组学和系统发育分析来进行检验。由于病毒的进化速度很高，当应用不充分的方法时，会导致系统发育假象，如长枝吸引，这项任务变得非常困难。可以证明，支持病毒作为第四个生命域的系统发育树是人为的。在大多数情况下，病毒中细胞基因同源物的存在最好用从细胞宿主到感染病毒的反复水平基因转移来解释，而不是相反。如今，没有确凿的证据证明存在病毒生命域，也没有证据证明病毒在细胞域起源中具有重大影响。
