Intra- and inter-specific variations in the mitochondrial gene orf138 of Ogura-type male-sterile cytoplasm from Raphanus sativus and Raphanus raphanistrum

In order to gain a better understanding of the evolution of Ogura male-sterile cytoplasm in radish, a large-scale sequence analysis of mitochondrial orf138 was conducted using 107 Japanese wild radishes, 29 cultivated radishes and seven Raphanus raphanisturum. A single approximately 0.8-kb fragment containing the orf138 locus was amplified from each plant by PCR, and the nucleotide sequence of an entire coding region of orf138 was determined by direct-sequencing procedures. An identical sequence to the published orf138 (Type A) was identified in Japanese wild radish, including a single plant in a population near Kagoshima prefecture where Ogura (1968) first found ’Ogura male-sterile radish’. Thus, it was confirmed that the ’Ogura male-sterile cytoplasm’ was derived from Japanese wild radish, with a Type A orf138 sequence, growing in this area. A total of six nucleotide changes and a single insertion/deletion (indel) were found in orf138 from both wild and cultivated radishes. By a combination of mutations, the orf138 sequences of the 143 radish plants were classified into nine types. Based on the pattern of mutations and the distribution of orf138 variants, it was concluded that the orf138 variants are derived from Type B or C, after Ogura-type cytoplasm was introduced from R. raphanistrum into Japanese wild radish.