Abstract:

C-U RNA editing exists in plant mitochondrial genome， and it can be divided into complete editing and partial editing. There are two copies of atpA gene in the mitochondrial genomes of cytoplasmic male sterile （CMS） line and maintainer line of cotton， indicating gene duplication. However， the impact of atpA gene duplication on RNA editing rate is still unclear. In this study， the specific sequences of each copy of atpA gene were cloned by Southern blot and choromosomal walking methods， showing that one copy was intact and the other copy was truncated in each line. The corresponding cDNAs were further amplified with RT-PCR and circular RT-PCR methods. The sequencing results showed that both the intact copy and the truncated copy of atpA gene in CMS and maintainer line were transcribed. There were 6 RNA editing sites in the intact atpA copies， and 4 RNA editing sites in the truncated copies. The RNA editing rates of the 6 sites of intact copy in maintainer line were 100%； while the RNA editing rates of the 6 sites of intact copy in CMS line were 100%， 85%， 100%， 92%， 100%， 100%， respectively. The editing rates of the 4 sites of the truncated copy in maintainer line were 55%， 37%， 55%， 27%， respectively； while the RNA editing rates of the 4 sites of the truncated copy in CMS line were 100%， 90%， 100%， 100%， respectively. It was speculated that the truncated copy in the maintaining line bears less selective pressure and may have lost its function； while the truncated atpA copy in the CMS line was still under high selective pressure and was likely to have new functions.

Key words: cotton, mitochondrial genome, atpA, gene duplication, RNA editing

摘要：

植物线粒体基因组中存在RNA编辑（C-U）现象，且有完全编辑和部分编辑之分。棉花细胞质雄性不育（cytoplasmic male sterile，CMS）系和保持系线粒体基因组中atpA基因各有两个拷贝，存在基因加倍现象，但atpA基因加倍对其RNA编辑率的影响尚不清楚。通过Southern blot、染色体步移技术确定出该基因每个拷贝具体的DNA序列，发现一个拷贝是完整的，一个拷贝是截短的。用RT-PCR、环化RT-PCR方法扩增出每个拷贝相应的cDNA，结果表明：棉花CMS系和保持系atpA基因完整拷贝和截短型拷贝都转录。完整拷贝、截短型拷贝中分别存在6、4个RNA编辑位点。完整拷贝6个RNA编辑位点在保持系中的编辑率都是100%；在CMS系中编辑率分别是100%、85%、100%、92%、100%、100%。截短型拷贝4个位点在保持系中的编辑率分别是55%、37%、55%、27%；在CMS系中编辑率分别是100%、90%、100%、100%。据此推测截短型拷贝在保持系中承受选择压较小，很可能已失去功能；而在CMS系中仍承受较大选择压，很可能具有新的功能。

关键词: 棉花, 线粒体基因组, atpA, 基因加倍, RNA编辑