MOLECULAR BASIS OF INTERORGANELLAR TRANSLOCATION IN WHEAT

本研究的目的是探讨细胞器基因组，即叶绿体和线粒体之间的遗传通量。系统地追踪了小麦叶绿体基因向线粒体DNA的细胞器间易位。通过限制性内切酶酶切或PCR扩增，构建了55个探针，共涉及70个叶绿体基因，其中包括所有的蛋白质编码基因和rRNA基因。将这些探针与覆盖小麦线粒体DNA主拷贝的14个粘粒克隆杂交，Southern杂交分析表明，含有20个基因的12个探针与线粒体DNA克隆杂交呈阳性，表明这些基因发生了易位。与其他禾本科植物如水稻和玉米相比，易位片段相对较小（0.3kbp至3.0kbp）。这些易位的叶绿体基因的总长度不足以解释被子植物线粒体基因组的巨大规模，它们与叶绿体DNA和线粒体主环DNA的同源性分别为14.6%（19.7kbp/135 kbp）和4.6%（19.7kbp/430 kbp）。易位基因在叶绿体DNA上的位置没有偏向性。将叶绿体易位基因定位在小麦线粒体DNA主环的物理图谱上，大部分易位基因分布在整个主环中，但也有部分基因聚集在与易位相关的热点区域。叶绿体基因在小麦线粒体DNA中的易位方式与水稻和玉米有很大不同，表明线粒体基因组具有可塑性。

The present study is aimed to investigate the genetic flux between organellar genomes, namely chloroplast and mitochondria. Interorganellar translocation of chloroplast genes into the mitochondrial DNA was systematically traced in wheat. Fifty-five probes responsible for 70 chloroplast genes, in which all protein-coding genes and rRNA genes are included, were constructged by digestion with the appropriate restriction endonucleases or PCR amplification. These probes were hybridized to the 14 cosmid clones which cover the entire part of a master copy of wheat mitochondria DNA.Southern hybridization analysis showed that twelve probes containing 20 genes gave positive signals to the mtDNA clones, showing the translocations of these genese. Translocated segments were relatively small (0.3kbp to 3.0kbp) in comparison to other grasses such as rice and maize. These positions are estimated to share 14.6% (19.7kbp/135kbp) of cpDNA and 4.6% (19.7kbp/430kbp) of mitochondrial master circle DNA.The total length of the translocated chloroplast genes is not enough to explain the enormous size of angiosperm mitochondrial genome. The positions of tranlocated genes on the chloroplast DNA were not biased. Translocated chloroplast genes were mapped on the physical map of a master circle of wheat mtDNA.Most tranlocated genes were dispersed throughout the wheat mitochondrial master circle, but some genes were clustered in the specific region consisting of hot spot related to translocations . The translocation modes of chloroplast genes into the wheat mtDNA greatly differed from those of rice and maize, showing the plasticity of mitochondrial genome.