| Male sterility is a biological phenomenon and widely occurring gboth in animals and plants. Both genic male sterility and cytoplasmic male sterility have been observed in plants. Genic male sterility is controlled by nuclear genes, and cytoplasmic male sterility is governed by cytoplasmic genes. Corresponding restoration genes in the nucleus could restore their pollen fertility.There are these types of Cytoplasmic Male Sterility in maize, T type(Texas), C type(Charrua) and S type(USDA). S type cytoplasmic male sterility(CMS-S) is the most common type of CMS in maize, it is gametophyte. In contrast, T type and C type of CMS are sporophyte. Besides the major fertility restoration gene, Rf3 for CMS-S, other restoration loci, such as Rf9、Rf III and Rf IVcould also restore the fertility of CMS-S. In total, we know little about the genetic basis of fertility restoration to CMS-S. In this study, A CMS-S line, S-Mo17 rfrfand 360 inbred lines were used to constructa testcrossing association mapping panel and genome-wide identification of genetic loci for fertility restoration ability(including pollen fertility, anther exsertion and pollen shedding) to CMS-S was firstly conducted with this association mapping panel in three environments including Hainan, Wuhan and Heilongjiang. The main results are as follows:1. Pollen in S-Mo17 rfrf was aborted absolutely and no anther exsertion and pollen shedding at all. Performance of the three traits is basically fit to normal distributions, and the traits varied largely. So they are complex quantitative traits. Correlation analysis showed that the significant positive correlation among pollen fertile, anther exsertion and pollen shedding. And the correlation between pollen fertility and pollen shedding was stronger than that between pollen fertility and anther exsertion. Crossections of the anthers with different pollen fertility revealed the anthers without pollen shedding had abnormal thickened fibrous layer, comparing to normal anthers.2. A total of 19 significant loci including Rf3 were identified to be associated with pollen fertility(<1.8×10-6, a=1)through genome-wide association study(GWAS). These loci are located on chromosome 2, 3, 5,8and 10. Among these significant loci, individual locus explained 5.62%~28.26% of phenotypic variation. Rf3 alone explained25.33%~28.26%of phenotypic variation. Combined analysis showed that these 19 loci explained 60.93% of phenotypic variation in total, thus pyramiding of the favorite alleles at these loci could increase pollen fertility.3. For the trait of anther exsertion, three significant loci were detected on chromosome 2, 3 and5 by GWAS respectively. In addition, Rf3 was identified. Individual locus explained 8.48%~ 9.26% of phenotypic variation. A total of eight significant loci were revealed by GWAS. These loci distributed on chromosome 2, 3 and 9. The locus Rf3 also was detected. Individual locusexplained9.2%-15.75%of phenotypic variation.4. Totally 83 candidate genes were predicted in the 50 kb regions up and down stream of the significant loci for pollen fertility, anther exsertion and pollen shedding. Based on the information of gene annotation in the B73 reference genome, the candidates encodes PPR proteins(pentatricopeptide repeat protein), transcription factors, and proteins associated with RNA editing, and the pathway for auxin and pollen development regulation.Through GWAS, we identified 19, 3and 8significant loci associated with pollen fertility, anther exsertion and pollen shedding, respectively. This demonstrated that multiple loci were involved in fertility restoration to CMS-S in this panel. At the same time, the significant SNP associated with Rf3 could provide useful information for fine mapping of this gene. Correlation analysis and comparison of the significant loci for the three traits revealed that they had different genetic architecture and the genetic bases between of pollen shedding and pollen fertility is relatively closer. |
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