Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA.
Nature. 2020 Dec;588(7836):141-145. doi: 10.1038/s41586-020-2924-2. Epub 2020 Nov 18.
Endogenous viral elements (EVEs)-viruses that have integrated their genomes into those of their hosts-are prevalent in eukaryotes and have an important role in genome evolution. The vast majority of EVEs that have been identified to date are small genomic regions comprising a few genes, but recent evidence suggests that some large double-stranded DNA viruses may also endogenize into the genome of the host. Nucleocytoplasmic large DNA viruses (NCLDVs) have recently become of great interest owing to their large genomes and complex evolutionary origins, but it is not yet known whether they are a prominent component of eukaryotic EVEs. Here we report the widespread endogenization of NCLDVs in diverse green algae; these giant EVEs reached sizes greater than 1 million base pairs and contained as many as around 10% of the total open reading frames in some genomes, substantially increasing the scale of known viral genes in eukaryotic genomes. These endogenized elements often shared genes with host genomic loci and contained numerous spliceosomal introns and large duplications, suggesting tight assimilation into host genomes. NCLDVs contain large and mosaic genomes with genes derived from multiple sources, and their endogenization represents an underappreciated conduit of new genetic material into eukaryotic lineages that can substantially impact genome composition.
内源性病毒元件（EVEs）——将其基因组整合到宿主基因组中的病毒——在真核生物中很普遍，在基因组进化中具有重要作用。迄今为止，已鉴定出的绝大多数 EVEs 都是由少数几个基因组成的小基因组区域，但最近的证据表明，一些大型双链 DNA 病毒也可能内源性整合到宿主基因组中。核质大 DNA 病毒（NCLDVs）因其庞大的基因组和复杂的进化起源而最近备受关注，但目前尚不清楚它们是否是真核 EVEs 的主要组成部分。在这里，我们报告了 NCLDVs 在各种绿藻中的广泛内源性化；这些巨型 EVEs 的大小超过 100 万个碱基对，在一些基因组中包含多达约 10%的总开放阅读框，大大增加了真核生物基因组中已知病毒基因的规模。这些内源性元件通常与宿主基因组位点共享基因，并包含大量剪接体内含子和大片段重复，表明它们与宿主基因组紧密同化。NCLDVs 具有庞大且镶嵌的基因组，其中包含来自多个来源的基因，它们的内源性化代表了新遗传物质进入真核谱系的一个被低估的途径，这可能会对基因组组成产生重大影响。
