Cytoplasmic Male Sterility and Mitochondrial Genome Variations in Radish

Abstract

The first CMS found in radish was Ogura CMS and it has been widely used in Brassicaceae crops. CMS named ‘UK-1,’ was reported, whereas more recently ‘NWB’ CMS was detected. A CMS radish that showed a similar phenotype to ‘NWB’ CMS was identified in an accession collected from Uzbekistan. This CMS was named as ‘DCGMS.’ ‘DCGMS’ differed from Ogura CMS in all the features investigated, whereas molecular studies revealed that ‘DCGMS’ was the same as ‘NWB.’ The gene orf138 was responsible for Ogura CMS. Nine types of orf138 sequences have been identified in wild and cultivated radishes. The orf125 of ‘Kosena’ and H-type orf138 of ‘UK-1’ are variants of orf138. Next-generation sequencing (NGS) has revolutionized studies on the plant mitochondrial genome, and the complete nucleotide sequences of the mitochondrial genomes of eight radish cultivars have been elucidated. The size of the radish mitochondrial genome ranged from 239,186 bp for ‘DCGMS’ to 258,426 bp for ‘MS-gensuke’, which contains the Ogura cytoplasm. Close examinations indicated that the eight radish mitochondrial genomes were classified into five types. Comparative genome sequencing unambiguously proved that the mitochondrial genomes of ‘DCGMS’ and ‘MS-gensuke’ differ from each other. Apart from ‘Black radish,’ no other radish contains a homologous sequence to orf463 , which is responsible for CMS in ‘DCGMS.’ More NGS data will clarify evolutionary and phylogenetic relationships between the various mitochondrial genomes of radish.