Adams K L, Clements M J, Vaughn J C
Department of Zoology, Miami University, Oxford, OH 45056, USA.
J Mol Evol. 1998 Jun;46(6):689-96. doi: 10.1007/pl00006349.
The Peperomia polybotrya coxI gene intron is the only currently reported group I intron in a vascular plant mitochondrial genome and it likely originated by horizontal transfer from a fungal donor. We provide a clearer picture of the horizontal transfer and a portrayal of the evolution of the group I intron since it was gained by the Peperomia mitochondrial genome. The intron was transferred recently in terms of plant evolution, being restricted to the single genus Peperomia among the order Piperales. Additional support is presented for the suggestion that a recombination/repair mechanism was used by the intron for integration into the Peperomia mitochondrial genome, as a perfect 1:1 correspondence exists between the intron's presence in a species and the presence of divergent nucleotide markers flanking the intron insertion site. Sequencing of coxI introns from additional Peperomia species revealed that several mutations have occurred in the intron since the horizontal transfer, but sequence alterations have not caused frameshifts or created stop codons in the intronic open reading frame. In addition, two coxI pseudogenes in Peperomia cubensis were discovered that lack a large region of coxI exon 2 and contain a truncated version of the group I intron that likely cannot be spliced out.
豆瓣绿coxI基因内含子是目前在维管植物线粒体基因组中唯一报道的I类内含子，它可能起源于从真菌供体的水平转移。我们对水平转移有了更清晰的认识，并描绘了自豆瓣绿线粒体基因组获得I类内含子以来其进化过程。就植物进化而言，该内含子是最近转移的，仅局限于胡椒目下的单属豆瓣绿。有更多证据支持以下观点：该内含子通过重组/修复机制整合到豆瓣绿线粒体基因组中，因为内含子在一个物种中的存在与内含子插入位点侧翼的不同核苷酸标记的存在之间存在完美的1:1对应关系。对其他豆瓣绿物种的coxI内含子进行测序发现，自水平转移以来，该内含子发生了几次突变，但序列改变并未导致内含子开放阅读框发生移码或产生终止密码子。此外，在古巴豆瓣绿中发现了两个coxI假基因，它们缺少coxI外显子2的大片区域，并包含一个可能无法剪接出的I类内含子截短版本。
