Remarkably little is known about the diversity and evolution of RNA viruses in unicellular eukaryotes. We screened a total of 570 transcriptomes from the Marine Microbial Eukaryote Transcriptome Sequencing Project that encompasses a wide diversity of microbial eukaryotes, including most major photosynthetic lineages (i.e. the microalgae). From this, we identified thirty new and divergent RNA virus species, occupying a range of phylogenetic positions within the overall diversity of RNA viruses. Approximately one-third of the newly described viruses comprised single-stranded positive-sense RNA viruses from the order Lenarviricota associated with fungi, plants, and protists, while another third were related to the order Ghabrivirales, including members of the protist and fungi-associated Totiviridae. Other viral species showed sequence similarity to positive-sense RNA viruses from the algae-associated Marnaviridae, the double-stranded RNA (ds-RNA) Partitiviridae, as well as tentative evidence for one negative-sense RNA virus related to the Qinviridae. Importantly, we were able to identify divergent RNA viruses from distant host taxa, revealing the ancestry of these viral families and greatly extending our knowledge of the RNA viromes of microalgal cultures. Both the limited number of viruses detected per sample and the low sequence identity to known RNA viruses imply that additional microalgal viruses exist that could not be detected at the current sequencing depth or were too divergent to be identified using sequence similarity. Together, these results highlight the need for further investigation of algal-associated RNA viruses as well as the development of new tools to identify RNA viruses that exhibit very high levels of sequence divergence.

中文翻译：

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揭示单细胞藻类转录组中 RNA 病毒的多样性和进化

值得注意的是，人们对单细胞真核生物中 RNA 病毒的多样性和进化知之甚少。我们从海洋微生物真核生物转录组测序项目中筛选了总共 570 个转录组，该项目涵盖了多种多样的微生物真核生物，包括大多数主要的光合谱系（即微藻）。由此，我们确定了三十种新的和不同的 RNA 病毒种，在 RNA 病毒的整体多样性中占据了一系列系统发育位置。大约三分之一的新描述病毒包含来自与真菌、植物和原生生物相关的 Lenarviricota 目的单链正链 RNA 病毒，而另外三分之一与 Ghabrivirales 目相关，包括原生生物和真菌相关的成员病毒科。其他病毒物种显示出与藻类相关的 Marnaviridae、双链 RNA (ds-RNA) Partitiviridae 的正义 RNA 病毒的序列相似性，以及与 Qinviridae 相关的一种负义 RNA 病毒的初步证据。重要的是，我们能够从遥远的宿主类群中识别出不同的 RNA 病毒，揭示了这些病毒家族的祖先，并极大地扩展了我们对微藻培养物 RNA 病毒组的了解。每个样本检测到的病毒数量有限以及与已知 RNA 病毒的低序列同一性都意味着存在其他微藻病毒，这些病毒无法在当前测序深度下检测到，或者差异太大而无法使用序列相似性进行识别。一起，