Institute of Evolution & Marine Biodiversity and College of Fisheries, Ocean University of China, Qingdao 266003, China.
Key Laboratory of Mariculture (OUC), Ministry of Education, Qingdao 266003, China.
Int J Mol Sci. 2021 Mar 3;22(5):2546. doi: 10.3390/ijms22052546.
Determination and comparisons of complete mitochondrial genomes (mitogenomes) are important to understand the origin and evolution of mitochondria. Mitogenomes of unicellular protists are particularly informative in this regard because they are gene-rich and display high structural diversity. Ciliates are a highly diverse assemblage of protists and their mitogenomes (linear structure with high A+T content in general) were amongst the first from protists to be characterized and have provided important insights into mitogenome evolution. Here, we report novel mitogenome sequences from three representatives ( sp., cf. , and ) in two dominant ciliate lineages. Comparative and phylogenetic analyses of newly sequenced and previously published ciliate mitogenomes were performed and revealed a number of important insights. We found that the mitogenomes of these three species are linear molecules capped with telomeric repeats that differ greatly among known species. The genomes studied here are highly syntenic, but larger in size and more gene-rich than those of other groups. They also all share an AT-rich tandem repeat region which may serve as the replication origin and modulate initiation of bidirectional transcription. More generally we identified a split version of , a cytochrome c maturation-related gene that might be a derived character uniting taxa in the subclasses Hypotrichia and Euplotia. Finally, our mitogenome comparisons and phylogenetic analyses support to reclassify from the subclass Oligotrichia to the subclass Hypotrichia. These results add to the growing literature on the unique features of ciliate mitogenomes, shedding light on the diversity and evolution of their linear molecular architecture.
确定和比较完整的线粒体基因组（mitogenomes）对于理解线粒体的起源和进化非常重要。单细胞原生动物的线粒体基因组在这方面特别有意义，因为它们基因丰富，结构多样性高。纤毛原生动物是一个高度多样化的原生动物组合，它们的线粒体基因组（通常具有线性结构和高 A+T 含量）是最早被描述的原生动物线粒体基因组之一，为线粒体基因组的进化提供了重要的见解。在这里，我们报告了两个优势纤毛动物谱系中三个代表种（sp.，cf. ，和 ）的新线粒体基因组序列。对新测序和以前发表的纤毛动物线粒体基因组进行了比较和系统发育分析，揭示了一些重要的见解。我们发现，这三个物种的线粒体基因组是线性分子，末端带有端粒重复序列，这些序列在已知物种中差异很大。本研究中的基因组高度同线性，但比其他组的基因组更大，基因更丰富。它们还都共享一个富含 AT 的串联重复区，该重复区可能作为复制起点，并调节双向转录的起始。更普遍的是，我们鉴定出了一个分裂版本的 ，这是一个与细胞色素 c 成熟相关的基因，可能是将 Hypotrichia 和 Euplotia 亚纲的分类群联合起来的衍生特征。最后，我们的线粒体基因组比较和系统发育分析支持将 从 Oligotrichia 亚纲重新分类到 Hypotrichia 亚纲。这些结果增加了关于纤毛动物线粒体基因组独特特征的文献，揭示了它们线性分子结构的多样性和进化。
