Turmel Monique, Otis Christian, Lemieux Claude
Département de Biochimie et de Microbiologie, Université Laval, Québec, Québec G1K 7P4, Canada.
Plant Cell. 2003 Aug;15(8):1888-903. doi: 10.1105/tpc.013169.
Mitochondrial DNA (mtDNA) has undergone radical changes during the evolution of green plants, yet little is known about the dynamics of mtDNA evolution in this phylum. Land plant mtDNAs differ from the few green algal mtDNAs that have been analyzed to date by their expanded size, long spacers, and diversity of introns. We have determined the mtDNA sequence of Chara vulgaris (Charophyceae), a green alga belonging to the charophycean order (Charales) that is thought to be the most closely related alga to land plants. This 67,737-bp mtDNA sequence, displaying 68 conserved genes and 27 introns, was compared with those of three angiosperms, the bryophyte Marchantia polymorpha, the charophycean alga Chaetosphaeridium globosum (Coleochaetales), and the green alga Mesostigma viride. Despite important differences in size and intron composition, Chara mtDNA strikingly resembles Marchantia mtDNA; for instance, all except 9 of 68 conserved genes lie within blocks of colinear sequences. Overall, our genome comparisons and phylogenetic analyses provide unequivocal support for a sister-group relationship between the Charales and the land plants. Only four introns in land plant mtDNAs appear to have been inherited vertically from a charalean algar ancestor. We infer that the common ancestor of green algae and land plants harbored a tightly packed, gene-rich, and relatively intron-poor mitochondrial genome. The group II introns in this ancestral genome appear to have spread to new mtDNA sites during the evolution of bryophytes and charalean green algae, accounting for part of the intron diversity found in Chara and land plant mitochondria.
线粒体DNA(mtDNA)在绿色植物的进化过程中发生了根本性的变化,但对于该门类中mtDNA进化的动态变化却知之甚少。陆地植物的mtDNA与迄今已分析的少数绿藻mtDNA不同,其大小扩展、间隔区较长且内含子多样。我们已经确定了普通轮藻(轮藻科)的mtDNA序列,普通轮藻是一种属于轮藻目的绿藻,被认为是与陆地植物关系最密切的藻类。将这条67,737碱基对的mtDNA序列(包含68个保守基因和27个内含子)与三种被子植物、苔藓植物地钱、轮藻目绿藻球囊藻以及绿藻绿中带藻的序列进行了比较。尽管在大小和内含子组成上存在重要差异,但轮藻的mtDNA与地钱的mtDNA惊人地相似;例如,68个保守基因中除了9个之外,其余都位于共线序列块内。总体而言,我们的基因组比较和系统发育分析明确支持了轮藻目与陆地植物之间的姐妹群关系。陆地植物mtDNA中似乎只有四个内含子是从轮藻藻类祖先垂直遗传而来的。我们推断,绿藻和陆地植物的共同祖先拥有一个紧密排列、基因丰富且内含子相对较少的线粒体基因组。在苔藓植物和轮藻目绿藻的进化过程中,这个祖先基因组中的II类内含子似乎扩散到了新的mtDNA位点,这也是轮藻和陆地植物线粒体中部分内含子多样性的原因。