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Identification of the earliest land plant based on the complete structure of chloroplast genome and RNA editing

基于叶绿体基因组完整结构和RNA编辑鉴定最早的陆地植物

基本信息

批准号：
14596003
负责人：
YOSHINAGA Koichi
金额：
$ 2.3万
依托单位：
Faculty of Science, Shizuoka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

One of the most important problem remaining in the phylogeny of green plants is which is the earliest land plant. We have determined the complete structure of the chloroplast genome from hornwort which had been expected as the earliest land plant. ML tree, based on 10,854 amino acid sites from 51 protein genes which are commonly found in the known chloroplast genomes, revealed that bryophytes are monophyletic with high statistical confidence and form the earliest branch, which diverged from all the other main lineages of land plants. The tree shows that the hornwort is basal in bryophytes.Another important problem, which is the direct ancestor of land plants, is in progress by analyzing the complete chloroplast structure from a charales which is expected as the direct ancestor of land plants.Much more RNA editing sites have been found in the hornwort chloroplast than those in the other chloroplasts. They contained 436 sites of U to C conversion which is not observed any seed plants. These editing converts more than half the genes functional, and creates the anticodon of a tRNA and the sequence required for splicing. Almost all the RNA editing complementing the mutation in the genes would be required in early land plants, because RNA editing is not seen in the algae but seen in almost all land plants.The sequence, named distant cis-recognition element (DGRE), complementary to the edited sequence has been observed within the same RNA. The premature transcript could form double stranded structure where there is a mismatch in base pairing. The mismatch could be recognized, and corrected by editing enzyme. This hypothetical mechanism for RNA editing will be proven in vitro.

在绿色植物的研究中，最重要的问题之一是哪一种植物是最早的陆生植物。我们已经确定了金鱼藻叶绿体基因组的完整结构，金鱼藻被认为是最早的陆地植物。基于已知叶绿体基因组中常见的51个蛋白质基因的10，854个氨基酸位点的ML树显示，短叶植物是单系的，具有高统计置信度，并且形成了最早的分支，该分支从所有其他陆地植物的主要谱系中分化出来。通过对拟作为陆生植物直接祖先的轮藻目植物叶绿体的结构分析，发现在金鱼藻叶绿体中存在着比其它叶绿体中多得多的RNA编辑位点。它们含有436个未观察到种子植物的U向C转化位点。这些编辑转换了一半以上的基因功能，并产生了tRNA的反密码子和剪接所需的序列。在早期的陆生植物中，几乎所有的RNA编辑都是基因突变的补充，因为RNA编辑在藻类中没有发现，但在几乎所有的陆生植物中都有发现。在同一RNA中观察到了与编辑序列互补的序列，称为远距离顺式识别元件（DGRE）。在碱基配对不匹配的情况下，早熟转录本可形成双链结构。错配可以被识别，并通过编辑酶进行校正。这种假设的RNA编辑机制将在体外得到证实。