ACCELERATED EVOLUTION OF PLANT MITOCHONDRIAL DNA

线粒体基因组在大小和基因上都经历了巨大的缩减 内容，因为他们的内生共生起源。此外，与 它们细菌祖先的基因组，大多数线粒体DNA 血统按顺序快速进化。显然，陆地植物是 例外，但我们最近发现了两个独立的 其替代率的植物谱系(天麻和车前) 四个线粒体蛋白和两个rRNA基因至少有5-30个 比典型的缓慢进化的植物线粒体高出几倍 基因组。关于这些主要的和潜在的 最近线粒体DNA突变率的增加包括：1) DNA修复缺陷，2)容易出错的DNA复制，以及3)容易出错 回溯处理。尽管几乎所有的植物线粒体mRNAs都是 经过广泛的RNA编辑，我们的数据表明线粒体 天麻或车前草中都不存在RNA编辑，即 事实上，他们的基因组已经被编辑了，这是不寻常的结果 广泛的后处理。这些数据支持以下假设 高强度、易出错的反向处理，即诱变反向 转录，然后重组回到基因组。 实验是为了在各种假说中进行检验，并 确定导致观测到的加速度的机制 车前草属和车前草属的线粒体DNA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.