Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada.
Hakai Institute, Heriot Bay, British Columbia, Canada.
Nat Commun. 2023 Nov 3;14(1):7049. doi: 10.1038/s41467-023-42807-0.
Microbial eukaryotes are important components of marine ecosystems, and the Marine Alveolates (MALVs) are consistently both abundant and diverse in global environmental sequencing surveys. MALVs are dinoflagellates that are thought to be parasites of other protists and animals, but the lack of data beyond ribosomal RNA gene sequences from all but a few described species means much of their biology and evolution remain unknown. Using single-cell transcriptomes from several MALVs and their free-living relatives, we show that MALVs evolved independently from two distinct, free-living ancestors and that their parasitism evolved in parallel. Phylogenomics shows one subgroup (MALV-II and -IV, or Syndiniales) is related to a novel lineage of free-living, eukaryovorous predators, the eleftherids, while the other (MALV-I, or Ichthyodinida) is related to the free-living predator Oxyrrhis and retains proteins targeted to a non-photosynthetic plastid. Reconstructing the evolution of photosynthesis, plastids, and parasitism in early-diverging dinoflagellates shows a number of parallels with the evolution of their apicomplexan sisters. In both groups, similar forms of parasitism evolved multiple times and photosynthesis was lost many times. By contrast, complete loss of the plastid organelle is infrequent and, when this does happen, leaves no residual genes.
微生物真核生物是海洋生态系统的重要组成部分，而海洋涡鞭毛类（MALVs）在全球环境测序调查中一直既丰富又多样。MALVs 是疑为其他原生生物和动物寄生虫的腰鞭毛目生物，但除了少数几个已描述物种的核糖体 RNA 基因序列之外，几乎没有其他数据，这意味着它们的大部分生物学和进化仍然未知。我们使用来自几个 MALVs 及其自由生活的近亲的单细胞转录组，表明 MALVs 是从两个不同的自由生活祖先独立进化而来的，它们的寄生进化是并行的。系统基因组学表明，一个亚组（MALV-II 和 -IV，或 Syndiniales）与一种新的自由生活、真核动物捕食者——eleftherids 有关，而另一个亚组（MALV-I，或 Ichthyodinida）与自由生活的捕食者 Oxyrrhis 有关，并保留了针对非光合质体的蛋白质。早期腰鞭毛藻类中光合作用、质体和寄生进化的重建表明，与它们的顶复门姐妹进化有许多相似之处。在这两个群体中，类似形式的寄生进化多次发生，光合作用多次丧失。相比之下，完整的质体细胞器的丧失很少发生，而当这种情况发生时，不会留下残留的基因。
