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 phenotype wherein plants cannot form normal male organs because of mitochondrial genes called CMS-causing genes. Many potato (Solanum tuberosum) varieties carry CMS-causing genes, resulting in pollen sterility that limits their use as male parents for breeding. In potato plants, three cytoplasmic types, T/beta, 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. In addition, although we previously identified open reading frame 137 (orf137) as a CMS-causing gene in a tomato (Solanum lycopersicum) CMS line created by asymmetric cell fusion between tomato and Solanum acaule, a wild potato relative, it remains unknown whether orf137 is associated with CMS phenotypes in potato plants. In this study, we first searched candidates for CMS-causing genes by comparing mitochondrial genomes of potato lines and detected open reading frame 320 (orf320) specific to T/beta cytoplasm. When orf320 with a mitochondrial transit peptide was overexpressed in tomatoes, phenotypes associated with male sterility, such as the premature degradation of anther tapetum and pollen abortion, were observed. We also investigated the presence of orf137 and orf320 in 154 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 candidate CMS-causing genes in T/beta and W/alpha-type cytoplasm will be valuable for accelerating future potato breeding.