Heterozygous alleles restore male fertility to cytoplasmic male-sterile radish (Raphanus sativus L.): a case of overdominance

Abstract

The practice of hybridization has greatly contributed to the increase in crop productivity. A major component that exploits heterosis in crops is the cytoplasmic male sterility (CMS)/nucleus-controlled fertility restoration (Rf) system. Through positional cloning, it is shown that heterozygous alleles (RsRf3-1/RsRf3-2) encoding pentatricopeptide repeat (PPR) proteins are responsible for restoring fertility to cytoplasmic male-sterile radish (Raphanus sativus L.). Furthermore, it was found that heterozygous alleles (RsRf3-1/RsRf3-2) show higher expression and RNA polymerase II occupancy in the CMS cytoplasmic background compared with their homozygous alleles (RsRf3-1/RsRf3-1 or RsRf3-2/RsRf3-2). These data provide new insights into the molecular mechanism of fertility restoration to cytoplasmic male-sterile plants and illustrate a case of overdominance.

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

“…By genotyping, we obtained only four plants with Rsrfo/ Rsrfo plus RsRf3-1/RsRf3-3 and five plants with Rsrfo/ Rsrfo plus RsRf3-1/RsRf3-4 in the above two populations consisting of 1200 and 1260 plants, respectively, indicating tight linkage between the loci RsRf3 and RsRfo. It was confirmed by previous DNA sequence alignment that a contig (42 kb) containing the RsRf3-1 allele and a bacterial artificial chromosome clone Bac64 (127 kb) carrying the RsRfo allele correspond to 7205-7256 and 7059-7139 kb, respectively, on chromosome 9 from Brassica rapa (Wang et al 2013).…”

“…Previous work showed that heterozygous alleles (RsRf3-1/RsRf3-2) can restore male fertility to radish CMS, but the homozygous alleles (RsRf3-1/RsRf3-1 or RsRf3-2/RsRf3-2) cannot (Wang et al 2013). In order to determine whether there are new alleles at the RsRf3 locus in radish lines, we designed a primer pair RsRf3-F/R that can amplify the full-length RsRf3 gene including partial 5 0 and 3 0 untranslated regions (all PCR primers are listed in Table 1).…”

“…Our previous work showed that both CMS line 9802A1 and its maintainer line 9802B1 have the Rsrfob allele and the RsRf3-1 allele (Wang et al 2008(Wang et al , 2013. In order to determine whether the RsRf3-3 allele and the RsRf3-4 allele at the RsRf3 locus involve fertility restoration to radish CMS in the plants carrying the non-restoring allele at the RsRfo locus, we performed the following crossing and genotyping work.…”

“…The PCR fragment amplified by the primer combination RsRfo dCAPS-F/R, using RsRfo as template, can be cut by the restriction endonuclease MseI. DNA extraction for genotyping was performed as described by Wang et al (2013) with minor modifications. About 5 mm 9 5 mm from young leaves was put into 96-well PCR plates.…”

Identification of heterotic loci associated with grain yield and its components using two CSSL test populations in maize

“…have reported that the accumulation of numerous rare superior alleles with positive dominance is an important contributor to the heterotic phenomenon in rice. Finally, Wang et al 59. have observed that the heterozygous alleles of pentatricopeptide repeat proteins ( RsRf3-1 / RsRf3-2 ) restore male fertility, an expressed overdominant effect, to cytoplasmic male-sterile radishes.…”