Cho Y, Palmer J D
Department of Biology, Indiana University at Bloomington 47405, USA.
Mol Biol Evol. 1999 Sep;16(9):1155-65. doi: 10.1093/oxfordjournals.molbev.a026206.
A group I intron has recently been shown to have invaded mitochondrial cox1 genes by horizontal transfer many times during the broad course of angiosperm evolution. To investigate the frequency of acquisition of this intron within a more closely related group of plants, we determined its distribution and inferred its evolutionary history among 14 genera of the monocot family Araceae. Southern blot hybridizations showed that 6 of the 14 genera contain this intron in their cox1 genes. Nucleotide sequencing showed that these six introns are highly similar in sequence (97.7%-99.4% identity) and identical in length (966 nt). Phylogenetic evidence from parsimony reconstructions of intron distribution and phylogenetic analyses of intron sequences is consistent with a largely vertical history of intron transmission in the family; the simplest scenarios posit but one intron gain and two losses. Despite this, however, striking differences in lengths of exonic co-conversion tracts, coupled with the absence of co-conversion in intron-lacking taxa, indicate that the six intron-containing Araceae probably acquired their introns by at least three and quite possibly five separate horizontal transfers. The highly similar nature of these independently acquired introns implies a closely related set of donor organisms.
最近研究表明，在被子植物漫长的进化过程中，I类内含子多次通过水平转移侵入线粒体细胞色素氧化酶亚基1（cox1）基因。为了研究在亲缘关系更近的一组植物中该内含子的获得频率，我们确定了它在单子叶天南星科14个属中的分布，并推断了其进化历史。Southern杂交显示，14个属中有6个属的cox1基因含有该内含子。核苷酸测序表明，这6个内含子在序列上高度相似（同一性为97.7%-99.4%），长度相同（966 nt）。来自内含子分布简约性重建和内含子序列系统发育分析的系统发育证据与该科内含子传递的主要垂直历史一致；最简单的情况是只有一次内含子获得和两次丢失。然而，尽管如此，外显子共转换片段长度的显著差异，以及缺乏内含子的分类群中不存在共转换，表明6个含有内含子的天南星科植物可能至少通过三次，很可能是五次独立的水平转移获得了它们的内含子。这些独立获得的内含子高度相似的性质意味着一组密切相关的供体生物。
