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 evolution1,2. The vast majority of EVEs that have been identified to date are small genomic regions comprising a few genes2, but recent evidence suggests that some large double-stranded DNA viruses may also endogenize into the genome of the host1. Nucleocytoplasmic large DNA viruses (NCLDVs) have recently become of great interest owing to their large genomes and complex evolutionary origins3-6, 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.

中文翻译：

---

巨型病毒的广泛内源化塑造了绿藻的基因组

内源性病毒元件 (EVE) - 将其基因组整合到宿主基因组中的病毒 - 在真核生物中普遍存在，并且在基因组进化中具有重要作用 1,2。迄今为止已鉴定出的绝大多数 EVE 是包含少数基因的小基因组区域 2，但最近的证据表明，一些大型双链 DNA 病毒也可能内源化到宿主的基因组中1。核质大 DNA 病毒 (NCLDVs) 最近因其大基因组和复杂的进化起源而引起了极大的兴趣 3-6，但尚不清楚它们是否是真核 EVE 的重要组成部分。在这里，我们报告了 NCLDV 在多种绿藻中的广泛内源化；这些巨型 EVE 的大小超过 100 万个碱基对，并且在某些基因组中包含多达 10% 的开放阅读框，大大增加了真核基因组中已知病毒基因的规模。这些内源化元件通常与宿主基因组基因座共享基因，并包含许多剪接体内含子和大量重复，表明与宿主基因组紧密同化。NCLDVs 包含具有来自多个来源的基因的大型嵌合基因组，它们的内源化代表了一种未被充分认识的新遗传物质进入真核细胞谱系的管道，可以显着影响基因组组成。这些内源化元件通常与宿主基因组基因座共享基因，并包含许多剪接体内含子和大量重复，表明与宿主基因组紧密同化。NCLDVs 包含具有来自多个来源的基因的大型嵌合基因组，它们的内源化代表了一种未被充分认识的新遗传物质进入真核细胞谱系的管道，可以显着影响基因组组成。这些内源化元件通常与宿主基因组基因座共享基因，并包含许多剪接体内含子和大量重复，表明与宿主基因组紧密同化。NCLDVs 包含具有来自多个来源的基因的大型嵌合基因组，它们的内源化代表了一种未被充分认识的新遗传物质进入真核细胞谱系的管道，可以显着影响基因组组成。