orf137 and orf320 are Candidates for Mitochondrial Genes Associated with W/alpha and T/beta-type Cytoplasmic Male Sterility in Potatoes
Cytoplasmic male sterility (CMS) is a plant phenotype that cannot form normal male organs due to mitochondrial genes called CMS-causing genes. Many potato (Solanum tuberosum) varieties carry CMS-causing genes, resulting in pollen sterility, which limits their use as male parents in potato breeding. In potatoes, three cytoplasmic types called Tbeta , W/alpha, and W/gamma are associated with CMS phenotypes. However, CMS-causing genes or loci have never been reported in T/beta and W/alpha-type cytoplasm. Furthermore, although we previouslyidentified orf137 as a CMS-causing gene in a tomato (S. lycopersicum) CMS line created by asymmetric cell fusion between tomato and potato wild relatives S. acaule, it remains unknown if orf137 is associated with the CMS phenotypes in potatoes. In this study, we first searched candidates for CMS-causing genes by comparing mitochondrial genomes of potato lines and detected orf320 specific to T/beta cytoplasm. When orf320 with mitochondrial transit peptide was overexpressed in tomatoes, phenotypes associated with male sterility, such as premature degradation of the anther tapetum, reduced number of pollens, and pollen abortion were observed. We also investigated the presence of orf137 and orf320 in cultivated potato varieties. The results revealed that orf137 was completely associated with W/alpha and T/beta-type cytoplasm, and orf320 was strongly associated with T/beta-type cytoplasm. The discovery of candidates for CMS-causing genes in T/beta and W/alpha-type cytoplasm will be valuable for accelerating future potato breeding.