Diplonemids are highly abundant heterotrophic marine protists. Previous studies showed that their strikingly bloated mitochondrial genome is unique because of systematic gene fragmentation and manifold RNA editing. Here we report a comparative study of mitochondrial genome architecture, gene structure and RNA editing of six recently isolated, phylogenetically diverse diplonemid species. Mitochondrial gene fragmentation and modes of RNA editing, which include cytidine-to-uridine (C-to-U) and adenosine-to-inosine (A-to-I) substitutions and 3' uridine additions (U-appendage), are conserved across diplonemids. Yet as we show here, all these features have been pushed to their extremes in the Hemistasiidae lineage. For example, Namystynia karyoxenos has its genes fragmented into more than twice as many modules than other diplonemids, with modules as short as four nucleotides. Furthermore, we detected in this group multiple A-appendage and guanosine-to-adenosine (G-to-A) substitution editing events not observed before in diplonemids and found very rarely elsewhere. With >1,000 sites, C-to-U and A-to-I editing in Namystynia is nearly 10 times more frequent than in other diplonemids. The editing density of 12% in coding regions makes Namystynia's the most extensively edited transcriptome described so far. Diplonemid mitochondrial genome architecture, gene structure and post-transcriptional processes display such high complexity that they challenge all other currently known systems.

中文翻译：

---

无国界基因片段化和 RNA 编辑：双克隆动物的偏心线粒体基因组。


双克隆虫是高度丰富的异养海洋原生生物。之前的研究表明，由于系统性的基因碎片和多种RNA编辑，它们的线粒体基因组惊人地膨胀，是独一无二的。在此，我们报告了对六种最近分离的、系统发育多样化的双克隆物种的线粒体基因组结构、基因结构和 RNA 编辑的比较研究。线粒体基因片段和 RNA 编辑模式，包括胞苷至尿苷 (C-to-U) 和腺苷-肌苷 (A-to-I) 替换以及 3' 尿苷添加（U-附件），均得到保留跨越双克隆亚目。然而，正如我们在这里所展示的，所有这些特征在 Hemistasiidae 谱系中都被推向了极端。例如，Namystynia karyoxenos 的基因片段化成的模块数量是其他双克隆动物的两倍多，模块短至四个核苷酸。此外，我们在该组中检测到多个 A 附属物和鸟苷到腺苷 (G-to-A) 取代编辑事件，这些事件以前在双倍菌素中未观察到，在其他地方也很少发现。 Namystynia 拥有 >1,000 个位点，C-to-U 和 A-to-I 编辑频率比其他双克隆动物中的近 10 倍。编码区 12% 的编辑密度使 Namystynia 成为迄今为止描述的编辑最广泛的转录组。双克隆线粒体基因组结构、基因结构和转录后过程显示出如此高的复杂性，以至于它们挑战了所有其他当前已知的系统。