Abstract
C-type cytoplasmic male sterility (CMS-C) is widely utilized for hybrid maize seed production. However, genetic mechanisms underlying the fertility restoration are very complicated. At present, there is a divergence on the number of fertility restorer genes in maize inbred line A619 for CMS-C. To further elucidate the restoring mechanism of A619, we used genetic analysis and molecular markers to confirm the restorer genes of maize inbred line A619 for C-type male sterile line C48-2 in this study. Firstly, the fertility segregations of (C48-2 × A619)F2 populations were investigated under three environments during 2013–2015. The segregation ratio of fertile and sterile plants in the F2 population fit to 15:1 via chi-square test and this result suggested that there are two dominant restorer genes in A619 for CMS-C, i.e., Rf4 and a novel gene named Rf*-A619. Next, based on the sequence differences between Rf4 and its recessive allelic rf4, a novel dominant marker F2/R2 was developed and validated to genotyping Rf4 in the F2 population. Through genotypic analysis, we found that there were a certain amount of fertile individuals without Rf4 which accounted for 3/16 in the F2 population via chi-square test at the 0.05 level. These results provided another proof to sustain that the inbred line A619 contains one additional restorer gene for CMS-C fertility restoration except Rf4. At last, we used one SSR marker which is tightly linked with the dominant restorer gene Rf5 to analyze those fertile plants without Rf4 in the F2 population. The PCR amplification results showed that Rf*-A619 is not allelic to Rf5 but a novel restorer gene for CMS-C. These results not only provide a basis for the mapping and characterization of a novel restorer gene but also give a new insight into the mechanism of CMS-C fertility restoration.
Highlights
CMS is a popular phenomenon in plant and fertility restorer genes (Rf ) and can rescue the fertility of CMS lines, and CMS/Rf systems in crops have been successfully utilized for human being because of the heterosis (Hu et al, 2014)
It is well known that A619 has the restore gene Rf4, so we named the other restore gene as Rf*-A619 following the nomenclatural rules of maize genetics
We developed a marker F2/R2 based on a 19-bp deletion in C48-2 compared with A619 to distinguish the Rf4 locus genotype (Fig. 2A)
Summary
CMS is a popular phenomenon in plant and fertility restorer genes (Rf ) and can rescue the fertility of CMS lines, and CMS/Rf systems in crops have been successfully utilized for human being because of the heterosis (Hu et al, 2014). Previous studies have demonstrated that fertility restoration of CMS-C is controlled by two dominant genes, Rf4 and Rf5, which separately located on chromosomes 8 and 5 (Chen, Luo & Ji, 1979; Sisco, 1991; Tang et al, 2001). Despite cloning and genetic complementation experiments indicating that GRMZM2G021276 is a candidate gene for CMS-C fertility restoration (Ren et al, 2012), the mechanism by which a transcription factor targeting the nucleus can overcome the deleterious effects of a mitochondrial defect remains mysterious. The above research results hinted A619 rescues the male sterility of CMS-C with highly complicate mechanisms
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