An insertion–deletion at a pentatricopeptide repeat locus linked to fertility transition to cytoplasmic male sterility in radish (Raphanus sativus L.)

The cytoplasmic male sterility (CMS)/nucleus-controlled fertility restoration (Rf) system has been widely applied in hybrid seed production and is an ideal model for dissecting the interaction between the nucleus and the mitochondrion. In this study, we identified an insertion–deletion (InDel) at a male fertility restoration locus (RsRf3) for CMS in radish (Raphanus sativus L.). A pentatricopeptide repeat (PPR)-encoding allele RsRf3-4 was found and encodes a predicted protein 579 amino acids in length, comprising 14 PPR domains and with a putative mitochondrial targeting signal. Sequence alignment revealed an InDel 26 bp in length and two point mutations between RsRf3-3 and RsRf3-4. Compared with RsRf3-4, the deletion changed the reading frame, resulting in a truncated amino acid sequence in RsRf3-3. A crossing test showed that the RsRf3-3 allele did not restore fertility to CMS in radish. In contrast, the RsRf3-4 allele cosegregated with fertility restoration to CMS in a segregation population. These results strongly suggest that the InDel at the RsRf3 locus could involve transition to fertility in CMS radish.