黄瓜线粒体类质粒 pC1、 pC4在品种间的分布及同源性研究

The Distribution and Homology of Mitochondrial Plasmid-like DNAs in Different Cucumber Varieties

在黄瓜（津研四号）线粒体中存在４种线粒体类质粒（ｐＣ１、ｐＣ２、ｐＣ３、ｐＣ４），对１４个黄瓜品种的线粒体类质粒分布情况进行了研究，发现在津春二号、津春五号、津新密刺、津绿四号和津研四号５个品种中存在线粒体类质粒，其余９个品种无线粒体类质粒，类质粒的存在有一定随机性。不同品种中的同一种类质粒间具有同源性。ｐＣ４类质粒不仅与自身的核ＤＮＡ同源，也与其他品种在核基因组有同源性，ｐＣ４同源序列在黄瓜核基因组中为多拷贝的，拷贝之间是不连续的。在丝瓜和西戎芦的核基因组中也有ｐＣ４的同源序列，因此，推测ｐＣ４可能在葫芦科分化的早期就已存在并整合于核中。某些品种缺乏类质粒是由于在进化过程中发生了类质粒的丢失。

Four kinds of mitochondrial plasmid-like DNA, designated pC1, pC2, pC3 and pC4, have been found in cucumber (Jinyan No.4). Their distribution in 14 Cucumber varieties was analyzed. Plasmid-like DNAs were detected in Jinchun No.2, Jinchun No.5, Jinxinmici, Jinlu No.4 and Jinyan No.4, and the rest 9 varieties contained no plasmid-like DNAs, suggesting that their distribution is irregular. There was homology among the same plasmid-like DNA family in different varieties. pC4 showed homology to the nuclear DNA of Jinyan No.4, in addition to the nuclear genomes of other 7 varieties either with plasmid-like DNAs or without. The homologous sequences of pC4 in the cucumber nuclear DNA were repetitive. Sequences homolgous to pC4 were also found in the nuclear genomes of towel gourd and pumpkin (other cucurbitaceous plant). Therefore, we propose that mitochondrial plasmid-like DNA occurred before cucumber diverged from cucurbit and had integrated into the nuclear DNA. The varieties without plasmid-like DNAs might lost them during evolution.