Cytoplasmic male sterility (CMS) observed in many plants leads defect in the production of functional pollen, while the expression of CMS is suppressed by a fertility restorer gene in the nuclear genome. Ogura CMS of radish is induced by a mitochondrial orf138, and a fertility restorer gene, Rfo, encodes a P-type PPR protein, ORF687, acting at the translational level. But, the exact function of ORF687 is still unclear. We found a Japanese variety showing male sterility even in the presence of Rfo. We examined the pollen fertility, Rfo expression, and orf138 mRNA in progenies of this variety. The progeny with Type H orf138 and Rfo showed male sterility when their orf138 mRNA was unprocessed within the coding region. By contrast, all progeny with Type A orf138 were fertile though orf138 mRNA remained unprocessed in the coding region, demonstrating that ORF687 functions on Type A but not on Type H. In silico analysis suggested a specific binding site of ORF687 in the coding region, not the 5′ untranslated region estimated previously, of Type A. A single nucleotide substitution in the putative binding site diminishes affinity of ORF687 in Type H and is most likely the cause of the ineffectiveness of ORF687. Furthermore, fertility restoration by RNA processing at a novel site in some progeny plants indicated a new and the third fertility restorer gene, Rfs, for orf138. This study clarified that direct ORF687 binding to the coding region of orf138 is essential for fertility restoration by Rfo.

在许多植物中观察到的细胞质雄性不育（CMS）导致功能性花粉的产生缺陷，而CMS的表达被核基因组中的育性恢复基因抑制。线粒体orf138诱导了萝卜的小仓CMS ，并且一个育性恢复基因Rfo编码一个在翻译水平起作用的P型PPR蛋白ORF687。但是，ORF687的确切功能仍不清楚。我们发现即使在Rfo的存在下，日本品种也显示出雄性不育。我们检查了该品种后代中的花粉育性，Rfo表达和orf138 mRNA。H型orf138和Rfo的后代当其orf138 mRNA在编码区内未加工时，表明雄性不育。相比之下，所有带有A型orf138的后代都可育，尽管orf138 mRNA在编码区中未加工，这表明ORF687在A型上起作用，但在H型上不起作用。计算机分析表明，ORF687在编码区中具有特异性结合位点，而在H推测的结合位点中的单个核苷酸取代会降低ORF687在H型中的亲和力，这很可能是ORF687失效的原因。此外，在某些子代植物的新位点通过RNA处理进行的育性恢复表明，新的和第三个育性恢复基因Rfs用于orf138。这项研究阐明，直接ORF687结合到orf138的编码区对于Rfo恢复生育至关重要。