Establishment of New Breeding Science by Biotechnology

报道了许多新的育种科学发现。其中一个重要的发现是植物线粒体基因组的稳定性。在大多数禾科植物中，含有叶绿体来源的trnH基因的线粒体序列在叶绿体来源和线粒体特异性序列连接的一个末端附近区域高度保守。RT-PCR、northern杂交、体外盖帽和核糖核酸酶保护实验结果表明，叶绿体衍生的trnH基因是由位于线粒体特异性序列的启动子转录而来。该区域的基因表达似乎与叶绿体衍生片段和线粒体特异性序列之间的连接序列的保存有关。因此，叶绿体来源的tRNA基因的表达对植物线粒体基因组的稳定性至关重要。先前的研究在线粒体DNA的叶绿体衍生序列上定位了9个水稻trna基因。我们检查了这些基因是否也在水稻线粒体中转录。Northern blot杂交显示，其中7个基因（trnC、trnF、trnH、trnM、trnN、trnS和trnW）被转录并被精确加工成成熟的trna。另外两个基因中的一个（trnP）在水稻线粒体中转录，但不能有效加工，而另一个（trnR）与原质体tRNA_<Arg>基因100%同源，但在水稻线粒体中没有转录。这些结果表明，9个pt衍生的trna中有7个可能用于植物线粒体蛋白质的生物合成，并支持植物线粒体基因组的稳定性。

Many findings for new breeding sciences were reported. One of the important findings was the stability of plant mitochondrial genome. Mitochondrial sequence that contains the chloroplast-derived trnH gene has been highly conserved in the region around one terminus of the junction between chloroplast-derived and mitochondrion-specific sequences in most of the gramineous plant analyzed. The results of RT-PCR, northern hybridization, in vitro capping and ribonuclease protection experiments show that the chloroplast-derived trnH gene is transcribed from a promoter that is located in the mitochondrion-specific sequence. Gene expression in this region seems to be correlated with the conservation of the sequence at the junction between chloroplast-derived fragment and the mitochondrion-specific sequence.Thus, expression of chloroplast-derived tRNA genes is important for the stability of plant mitochondrial genome. Previous investigations located nine of the genes for rice tRNAs on chloroplast-derived sequences in mitochondrial DNA.We examined whether these genes were also transcribed in the rice mitochondria. Northern blot hybridization revealed that seven of these genes (trnC, trnF, trnH, trnM, trnN, trnS and trnW) are transcribed and are precisely processed to mature tRNAs. One of the other two genes (trnP) is transcribed but cannot be processed efficiently, and the other (trnR), which has 100% identity to the original plastid tRNA_<Arg> gene, is not transcribed in rice mitochondria. These results suggest that seven of the nine pt-derived tRNAs may be utilized for biosynthesis of protein in plant mitochondria, and support for the stability of plant mitochondrial genome.