Laboratory of Genetic Engineering, Research Faculty of Agriculture, Hokkaido University, Sapporo, Hokkaido 060-8589, Japan.
Genetics. 2012 Dec;192(4):1347-58. doi: 10.1534/genetics.112.145409. Epub 2012 Sep 20.
Male gametogenesis in plants can be impaired by an incompatibility between nuclear and mitochondrial genomes, termed cytoplasmic male sterility (CMS). A sterilizing factor resides in mitochondria, whereas a nuclear factor, Restorer-of-fertility (Rf), restores male fertility. Although a majority of plant Rf genes are thought to encode a family of RNA-binding proteins called pentatrico-peptide repeat (PPR) proteins, we isolated a novel type of Rf from sugar beet. Two BACs and one cosmid clone that constituted a 383-kbp contig covering the sugar beet Rf1 locus were sequenced. Of 41 genes borne by the contig, quadruplicated genes were found to be associated with specific transcripts in Rf1 flower buds. The quadruplicated genes encoded a protein resembling OMA1, a protein known from yeast and mammals to be involved in mitochondrial protein quality control. Construction of transgenic plants revealed that one of the four genes (bvORF20) was capable of restoring partial pollen fertility to CMS sugar beet; the level of restoration was comparable to that evaluated by a crossing experiment. However, the other genes lacked such a capability. A GFP-fusion experiment showed that bvORF20 encoded a mitochondrial protein. The corresponding gene was cloned from rf1rf1 sugar beet and sequenced, and a solitary gene that was similar but not identical to bvORF20 was found. Genetic features exhibited by sugar beet Rf1, such as gene clustering and copy-number variation between Rf1 and rf, were reminiscent of PPR-type Rf, suggesting that a common evolutionary mechanism(s) operates on plant Rfs irrespective of the translation product.
植物中的雄性配子发生可以被核基因组和线粒体基因组之间的不兼容性所破坏，这种不兼容性被称为细胞质雄性不育（CMS）。一种不育因子位于线粒体中，而核因子恢复育性（Rf）则恢复雄性育性。尽管大多数植物 Rf 基因被认为编码一类称为五肽重复（PPR）蛋白的 RNA 结合蛋白，但我们从甜菜中分离出了一种新型的 Rf。两个 BAC 和一个 cosmid 克隆构成了一个 383-kbp 的 contig，覆盖了甜菜 Rf1 基因座。该 contig 上有 41 个基因，其中四倍化基因与 Rf1 花蕾中的特定转录本相关。四倍化基因编码的蛋白类似于 OMA1，酵母和哺乳动物中的 OMA1 蛋白已知参与线粒体蛋白质量控制。转植物的构建表明，四个基因中的一个（bvORF20）能够使 CMS 甜菜的花粉部分恢复育性；恢复水平与交叉实验评估的水平相当。然而，其他基因则没有这种能力。GFP 融合实验表明 bvORF20 编码一种线粒体蛋白。从 rf1rf1 甜菜中克隆了相应的基因并进行了测序，发现了一个与 bvORF20 相似但不完全相同的孤立基因。甜菜 Rf1 表现出的遗传特征，如基因聚类和 Rf1 与 rf 之间的拷贝数变异，与 PPR 型 Rf 相似，表明植物 Rf 无论其翻译产物如何，都存在共同的进化机制。
