Studies on Molecular Breeding by Functional Analysis of Rice Mitochondrial Genome

高等植物的线粒体基因组比其他真核生物的要大得多，也更复杂。基因组的结构复杂性与重复序列之间的重排和许多叶绿体衍生序列的存在有关。以下证据表明水稻线粒体基因组中的基因表达模式也是复杂和灵活的。通过体外封顶/核糖核酸酶保护实验和引物延伸分析，我们确定了线粒体基因的转录起始点。基因起始点周围的序列比对显示出一个保守的序列基序，特别是CRTA基序。两个基因簇RPS3-rpl16和nad3-rps12是相互分离的，在许多植物中作为单独的转录单位表达。在rrn26上游区域发现的76个碱基的序列在trnfM的上游区域是重复的，证明trnfM和rrn26的转录是从各自基因上游区域的这些序列开始的。另一方面，线粒体特异基因nad9与叶绿体衍生序列一起转录。这表明叶绿体衍生的序列被用作NAD9的启动子。

The mitochondrial genomes of higher plants are much larger and more complex than those of other eukaryotic organisms. The structural complexity of the genomes has been associated with rearrangements among repeated sequences and the presence of many chloroplast-derived sequences. Following evidence shows the mode of gene expression in the mitochondrial genome of rice is also complex and flexible.Using in vitro capping/ribonuclease protection experiments and primer extension analyzes, we identified the transcription initiation sites of mitochondrial genes. The alignment of sequences surrounding the initiation sites of genes revealed a conserved sequence motif, particularly CRTA motif.The two gene clusters rps3-rpl16 and nad3-rps12 are separated from each other and are expressed as the individual transcription units in many plants. However, the four genes were located within a region of 6kbp in rice mitochondria, and all four genes were co-transcribed.The 76 bp sequence found in the upstream region of rrn26 is duplicated in the upstream region of trnfM.It was demonstrated that the transcription of trnfM and rrn26 starts from these sequences in the upstream regions of the respective genes.A chloroplast-derived tRNA gene, trnH was transcribed in rice mitochondria using mitochondrial specific promoter sequence. On the other hand, the mitochondrial specific gene, nad9 was transcribed together with the chloroplast-derived sequence. It shows a chloroplast-derived sequence is utilized as a promoter for nad9.