Holst-Jensen A, Vaage M, Schumacher T, Johansen S
Department of Biology, University of Oslo, Norway.
Mol Biol Evol. 1999 Jan;16(1):114-26. doi: 10.1093/oxfordjournals.molbev.a026031.
We have characterized structural features and the distribution pattern of nuclear group I introns found in ribosomal DNA (rDNA) of closely related plant pathogenic fungi of the family Sclerotiniaceae. Sixteen introns, at two distinct positions in the small-subunit (SSU) and large-subunit (LSU) rDNA, were sequenced and analyzed among the 29 taxa included in the initial screening. Genera found to contain introns were Botrytis, Dumontinia, Encoelia, Grovesinia, Myriosclerotinia, and Sclerotinia. Secondary-structure analyses of the group I introns concluded that all belong to the common IC1 subclass. Interestingly, the SSU rDNA intron from Myriosclerotinia caricisampullacea contains an insertion-like sequence extension which may be a relic of an open reading frame. Incongruent branching patterns of intron-based and rDNA-based (internal transcribed spacer) phylogenetic trees suggest that the fungal host genomes and the group I introns do not share a common evolutionary history. A model to explain how horizontal intron transfers may have occurred among the closely related fungal taxa is proposed.
我们已经对核盘菌科密切相关的植物病原真菌核糖体DNA（rDNA）中发现的I类核内含子的结构特征和分布模式进行了表征。在初步筛选的29个分类单元中，对小亚基（SSU）和大亚基（LSU）rDNA中两个不同位置的16个内含子进行了测序和分析。发现含有内含子的属包括葡萄孢属、杜蒙菌属、恩氏盘菌属、格氏盘菌属、多菌核盘菌属和核盘菌属。对I类核内含子的二级结构分析得出结论，所有内含子均属于常见的IC1亚类。有趣的是，来自多菌核盘菌的SSU rDNA内含子包含一个类似插入序列的延伸，这可能是一个开放阅读框的遗迹。基于内含子和基于rDNA（内部转录间隔区）的系统发育树的不一致分支模式表明，真菌宿主基因组和I类核内含子没有共同的进化历史。提出了一个模型来解释水平内含子转移可能是如何在密切相关的真菌分类单元之间发生的。
