Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, United States of America.
PLoS One. 2011;6(10):e25836. doi: 10.1371/journal.pone.0025836. Epub 2011 Oct 5.
Early land plant mitochondrial genomes captured important changes of mitochondrial genome evolution when plants colonized land. The chondromes of seed plants show several derived characteristics, e.g., large genome size variation, rapid intra-genomic rearrangement, abundant introns, and highly variable levels of RNA editing. On the other hand, the chondromes of charophytic algae are still largely ancestral in these aspects, resembling those of early eukaryotes. When the transition happened has been a long-standing question in studies of mitochondrial genome evolution. Here we report complete mitochondrial genome sequences from an early-diverging liverwort, Treubia lacunosa, and a late-evolving moss, Anomodon rugelii. The two genomes, 151,983 and 104,239 base pairs in size respectively, contain standard sets of protein coding genes for respiration and protein synthesis, as well as nearly full sets of rRNA and tRNA genes found in the chondromes of the liverworts Marchantia polymorpha and Pleurozia purpurea and the moss Physcomitrella patens. The gene orders of these two chondromes are identical to those of the other liverworts and moss. Their intron contents, with all cis-spliced group I or group II introns, are also similar to those in the previously sequenced liverwort and moss chondromes. These five chondromes plus the two from the hornworts Phaeoceros laevis and Megaceros aenigmaticus for the first time allowed comprehensive comparative analyses of structure and organization of mitochondrial genomes both within and across the three major lineages of bryophytes. These analyses led to the conclusion that the mitochondrial genome experienced dynamic evolution in genome size, gene content, intron acquisition, gene order, and RNA editing during the origins of land plants and their major clades. However, evolution of this organellar genome has remained rather conservative since the origin and initial radiation of early land plants, except within vascular plants.
早期陆地植物的线粒体基因组在植物登陆时捕获了线粒体基因组进化的重要变化。种子植物的chondromes 显示出几个衍生特征，例如，基因组大小变化大、基因组内快速重排、丰富的内含子和高度可变的 RNA 编辑水平。另一方面，charophytic 藻类的chondromes 在这些方面仍然很大程度上是原始的，类似于早期真核生物的chondromes。这种转变何时发生一直是线粒体基因组进化研究中的一个长期存在的问题。在这里，我们报告了来自早期分化的苔类植物 Treubia lacunosa 和晚期进化的藓类植物 Anomodon rugelii 的完整线粒体基因组序列。这两个基因组大小分别为 151983 和 104239 个碱基对，包含呼吸和蛋白质合成的标准蛋白编码基因以及在 Marchantia polymorpha 和 Pleurozia purpurea 的苔类植物和 Physcomitrella patens 的chondromes 中发现的几乎完整的 rRNA 和 tRNA 基因。这两个chondromes 的基因顺序与其他苔类植物和藓类植物的chondromes 相同。它们的内含子含量，所有顺式剪接的 I 组或 II 组内含子，也与以前测序的苔类植物和藓类植物的chondromes 相似。这五个chondromes 加上来自角苔 Phaeoceros laevis 和 Megaceros aenigmaticus 的两个chondromes，首次允许对苔藓植物和维管植物三个主要谱系内和谱系间的线粒体基因组结构和组织进行全面比较分析。这些分析得出的结论是，在陆地植物及其主要分支的起源过程中，线粒体基因组在基因组大小、基因含量、内含子获取、基因顺序和 RNA 编辑方面经历了动态进化。然而，自从早期陆地植物的起源和最初辐射以来，这个细胞器基因组的进化仍然相当保守，除了在维管植物中。
