Mitogenome diversity is staggering among early branching animals with respect to size, gene density, content and order, and number of tRNA genes, especially in cnidarians. This last point is of special interest as tRNA cleavage drives the maturation of mitochondrial mRNAs and is a primary mechanism for mt-RNA processing in animals. Mitochondrial RNA processing in non-bilaterian metazoans, some of which possess a single tRNA gene in their mitogenomes, is essentially unstudied despite its importance in understanding the evolution of mitochondrial transcription in animals. We characterized the mature mitochondrial mRNA transcripts in a species of the octocoral genus Sinularia (Alcyoniidae: Octocorallia), and defined precise boundaries of transcription units using different molecular methods. Most mt-mRNAs were polycistronic units containing two or three genes and 5′ and/or 3′ untranslated regions of varied length. The octocoral specific, mtDNA-encoded mismatch repair gene, the mtMutS, was found to undergo alternative polyadenylation, and exhibited differential expression of alternate transcripts suggesting a unique regulatory mechanism for this gene. In addition, a long noncoding RNA complementary to the ATP6 gene (lncATP6) potentially involved in antisense regulation was detected. Mt-mRNA processing in octocorals possessing a single mt-tRNA is complex. Considering the variety of mitogenome arrangements known in cnidarians, and in general among non-bilaterian metazoans, our findings provide a first glimpse into the complex mtDNA transcription, mt-mRNA processing, and regulation among early branching animals and represent a first step towards understanding its functional and evolutionary implications.

中文翻译：

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八叶形中不存在tRNA标点的线粒体RNA加工。

在早期分支动物中，关于tRNA基因的大小，基因密度，含量和顺序以及数量，有丝分裂基因组的多样性令人震惊，尤其是在刺胞动物中。最后一点是特别有意义的，因为tRNA的切割驱动线粒体mRNA的成熟，并且是动物中mt-RNA加工的主要机制。尽管在了解动物线粒体转录过程中的重要性，但非百日咳后生动物中的线粒体RNA加工（其中一些在其线粒体基因组中只有一个tRNA基因）仍未被研究。我们表征了八倍体Sinularia（Alcyoniidae：Octocorallia）物种中成熟的线粒体mRNA转录本，并使用不同的分子方法定义了转录单位的精确边界。大多数mt-mRNA是多顺反子单元，包含两个或三个基因以及5'和/或3'长度可变的非翻译区。发现八齿特异性，mtDNA编码的错配修复基因mtMutS经历了交替的多聚腺苷酸化，并表现出交替转录本的差异表达，提示该基因具有独特的调控机制。此外，还检测到可能与反义调控有关的与ATP6基因（lncATP6）互补的长非编码RNA。具有单个mt-tRNA的八叶虫的Mt-mRNA加工非常复杂。考虑到cnidarians中已知的有丝分裂基因组排列的多样性，以及通常在非双尾后生动物中的有丝分裂基因组排列，我们的发现首次提供了复杂的mtDNA转录，mt-mRNA加工，