Cytoplasmic suppression of Ogura cytoplasmic male sterility in European natural populations of Raphanus raphanistrum

The Ogura cytoplasmic male sterility (CMS) of radish has been used for hybrid seed production in radish and Brassica crops. It is the only CMS system occurring in wild populations for which the gene responsible for sterility and a restorer gene have been formally identified. In Japan, gynodioecious populations of radish carrying Ogura or an Ogura-related cytoplasm have been described. The occurrence of restorer genes for the Ogura CMS in wild radish ( Raphanus raphanistrum ) in France led us to search for the corresponding male sterility gene ( orf138 ) in several natural populations in France, England and Lebanon. We detected the orf138 gene, by PCR, at low frequency, in three populations from France and one from Southern England. Further molecular characterization showed that these plants carried a cytoplasm closely related to the original Ogura cytoplasm, with a variant orf138 coding sequence, previously reported to be ancestral. We performed crosses with sterile and maintainer radish lines, to test the ability of this wild Ogura-related cytoplasm to induce sterility. Surprisingly, the European Ogura-related cytoplasm did not cause sterility. Northern blots and circular RT-PCR analyses showed that orf138 gene expression was impaired in these plants because of a novel cytoplasm-dependent transcript-processing site.