Free-living core dinoflagellates are commonly infected by members of two parasitic clades that are themselves closely related to dinoflagellates, the marine alveolates and perkinsids. These parasites are abundant and ecologically important, but most species have been difficult to observe directly or cultivate, so our knowledge of them is usually restricted to environmental 18S rRNA gene sequences, and genome-scale molecular data are not available for most species. Here, we report numerous syndinian parasites and one parasite that is sister to all known perkinsids from isolated single cells of diverse, free-living dinoflagellates. Of the 14 infected host cells collected, only five were noticeably infected via light microscopy at the time of collection. Single-cell transcriptome sequencing yielded relatively high transcriptomic coverage for parasites as well as their hosts. Host and parasite homologs were distinguished phylogenetically allowing us to infer a robust phylogenomic tree based on 198 genes. The tree showed one parasite belongs to an undescribed lineage that is sister to perkinsids, whereas the remainder are members of the syndinian clade. Close relatives of all these parasites have been observed in 18S rRNA gene surveys, but until now none had been linked to a specific host. These findings illustrate the efficacy of single-cell isolation and transcriptome sequencing as a strategy for gaining deeper insights into the evolutionary history and host relationships of hidden single-celled parasites.

中文翻译：

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单细胞转录组学揭示的甲藻宿主中隐藏的 syndinian 和 perkinsid 感染


自由生活的核心甲藻通常由两个寄生分支的成员感染，这两个寄生分支本身与甲藻密切相关，即海洋肺泡和帕金斯科。这些寄生虫数量丰富且具有重要的生态意义，但大多数物种很难直接观察或培养，因此我们对它们的了解通常仅限于环境 18S rRNA 基因序列，并且无法获得大多数物种的基因组规模分子数据。在这里，我们报道了许多 syndinian 寄生虫和一种寄生虫，它是来自各种自由生活的甲藻的分离单细胞中所有已知 perkinsids 的姐妹。在收集的 14 个感染宿主细胞中，只有 5 个在收集时通过光学显微镜明显感染。单细胞转录组测序对寄生虫及其宿主的转录组覆盖率相对较高。宿主和寄生虫同源物在系统发育上进行了区分，使我们能够根据 198 个基因推断出一个强大的系统发育树。这棵树显示一种寄生虫属于一个未描述的谱系，该谱系是 perkinsids 的姐妹，而其余的则是 syndinian 分支的成员。在 18S rRNA 基因调查中观察到所有这些寄生虫的近亲，但到目前为止还没有一个与特定宿主有关。这些发现说明了单细胞分离和转录组测序作为深入了解隐藏单细胞寄生虫的进化历史和宿主关系的策略的有效性。