Identification of promoter exchange at a male fertility restorer locus for cytoplasmic male sterility in radish (Raphanus sativus L.)

Abstract

The cytoplasmic male sterility (CMS)/nucleus-controlled fertility restoration (Rf) system is a major component that exploits hybrid vigor in crops. Here, we have identified a new pentatricopeptide repeat (PPR)-encoding allele at the RsRf3 locus linked to the fertility restoration to CMS in radish. This allele was named as RsRf3-5 and encodes a putative protein with 18 PPRs and a predicted mitochondrial targeting signal. Another allele RsRf3-6 encoding the same protein with RsRf3-5 possesses a different promoter region and has failed to restore fertility to CMS. The non-restoring allele RsRf3-7 encoding a predicted protein with 15 PPRs has an identical promoter region with RsRf3-6, suggesting that RsRf3-6 could result from a recent crossover between RsRf3-5 and RsRf3-7. Interestingly, the RsRf3-5 allele shows higher RNA expression levels in the CMS cytoplasmic background compared with the RsRf3-6 allele.