ACCELERATED EVOLUTION OF PLANT MITOCHONDRIAL DNA

线粒体基因组在大小和基因表达上经历了大规模的减少， 内容，因为它们的内共生起源。 此外，与 它们的细菌祖先的基因组，大多数线粒体DNA 谱系按顺序迅速进化。 陆地植物显然是 这是一个例外，但我们最近发现两个独立的 植物（天竺葵属和车前草）的谱系，其替代率 四种线粒体蛋白和两种rRNA基因的同源性至少为5-30 比典型的进化缓慢的植物线粒体高出一倍 基因组 对这些主要和潜在机制的假设 最近线粒体DNA突变率的增加包括：1） 缺陷的DNA修复，2）易错的DNA复制，和3）易错的 后处理 尽管几乎所有的植物线粒体mRNA都是 经过大量的RNA编辑，我们的数据表明， RNA编辑在天竺葵属或车前草属中均不发生， 事实上，由于异常的原因，他们的基因组已经被编辑了 大量的后处理 这些数据支持以下假设： 密集的、容易出错的逆向处理，即，诱变逆转 转录后重组回基因组。 提出实验来检验各种假设， 确定负责观察到的加速的机制， 天竺葵属和车前属植物线粒体DNA的进化。

Mitochondrial genomes have undergone massive reductions in size and gene content since their endosymbiotic origin. Furthermore, compared with the genomes of their bacterial ancestors, most mitochondrial DNA lineages evolve rapidly in sequence. Land plants are apparently the one exception to this, but we have very recently identified two independent lineages of plants (Pelargonium and Plantago) whose substitution rates for four mitochondrial protein and two rRNA genes are at least 5-30 times higher than those of typical, slowly-evolving plant mitochondrial genomes. Hypotheses for the mechanisms underlying these major and recent increases in mitochondrial DNA mutation rate include: 1) deficient DNA repair, 2) error-prone DNA replication, and 3) error-prone retroprocessing. Although virtually all plant mitochondrial mRNAs are subject to extensive RNA editing, our data indicate that mitochondrial RNA editing does not occur in either Pelargonium or Plantago, that in fact their genomes are already edited as a consequence of unusually extensive retroprocessing. These data support the hypothesis of intense, error-prone retroprocessing, i.e., mutagenic reverse transcription followed by recombination back into the genome. Experiments are proposed to test among the various hypotheses and to determine the mechanisms responsible for the observed acceleration in mitochondrial DNA evolution in Pelargonium and Plantago.