Multiple fertility restorer loci for cytoplasmic male sterility caused by mitochondrial gene orf137 in tomato

Cytoplasmic male sterility (CMS) in plants is caused by incompatibility between nuclear and cytoplasmic genetic information. Fertility can be restored through the action of fertility restorer (RF) genes, which are usually present in the nucleus. CMS lines of tomato (Solanum lycopersicum) caused by mitochondrial gene orf137 have been developed from asymmetric cell fusions, and in these lines, cultivated tomato served as a nuclear donor and its wild relative, S. acaule, as a cytoplasm donor. Although RF genes are present in wild relatives of tomato, no genetic or genomic information on the RF genes is yet available. This study reports an RF genetic locus, RF1, on chromosome 1 of S. pimpinellifolium LA1670 and S.  lycopersicum var. cerasiforme LA1673, which was revealed by bulked segregant analysis and sequencing. An additional RF locus, RF2, was identified on chromosome 2 of LA1670. The genomic sequence of S. cheesmaniae LA0166 was assembled using high-fidelity, long-read sequencing technology. Sequence comparisons identified further candidate RF genes on chromosome 1 of S. cheesmaniae LA0166. These results suggested that multiple gene loci control the fertility restoration trait in wild relatives of tomato.