Waller Ross F, Jackson Christopher J
School of Botany, University of Melbourne, Melbourne, Victoria, Australia.
Bioessays. 2009 Feb;31(2):237-45. doi: 10.1002/bies.200800164.
Mitochondrial genomes represent relict bacterial genomes derived from a progenitor alpha-proteobacterium that gave rise to all mitochondria through an ancient endosymbiosis. Evolution has massively reduced these genomes, yet despite relative simplicity their organization and expression has developed considerable novelty throughout eukaryotic evolution. Few organisms have reengineered their mitochondrial genomes as thoroughly as the protist lineage of dinoflagellates. Recent work reveals dinoflagellate mitochondrial genomes as likely the most gene-impoverished of any free-living eukaryote, encoding only two to three proteins. The organization and expression of these genomes, however, is far from the simplicity their gene content would suggest. Gene duplication, fragmentation, and scrambling have resulted in an inflated and complex genome organization. Extensive RNA editing then recodes gene transcripts, and trans-splicing is required to assemble full-length transcripts for at least one fragmented gene. Even after these processes, messenger RNAs (mRNAs) lack canonical start codons and most transcripts have abandoned stop codons altogether.
线粒体基因组代表了源自祖先α-变形菌的残余细菌基因组，这种α-变形菌通过古老的内共生产生了所有线粒体。进化过程极大地减少了这些基因组，然而，尽管相对简单，但在整个真核生物进化过程中，它们的组织和表达却产生了相当大的新奇之处。很少有生物像甲藻原生生物谱系那样彻底地重新设计其线粒体基因组。最近的研究表明，甲藻线粒体基因组可能是所有自由生活的真核生物中基因最贫乏的，仅编码两到三种蛋白质。然而，这些基因组的组织和表达远非其基因含量所显示的那么简单。基因复制、片段化和重排导致了基因组组织膨胀且复杂。广泛的RNA编辑随后对基因转录本进行重新编码，并且需要反式剪接来组装至少一个片段化基因的全长转录本。即使经过这些过程，信使RNA（mRNA）仍缺乏典型的起始密码子，并且大多数转录本完全舍弃了终止密码子。
