| Maize is one of the most important cereal crops in the world. Increasing maize yield has become the primary goal of maize breeding. However, knowledge of genes related to yield and yield-related traits and hybrid vigour is very limited. Thus, genetic study on yield-related traits is very important for maize genetic improvement. With the increasing of labour cost, the use of CMS(cytoplasmic male sterility) lines in hybrid seed production is more and more important. Maize S type of CMS(CMS-S) is the most widely used one in the three main CMS groups. It is gametophyte derived male sterile type. Genetic identification and cloning of fertility restoration genes to CMS-S is crucial for the application of heterosis in maize production. In this study, a testcross association mapping population derived from crosses between a CMS-S line and a set of association mapping panel. Eight BC1 populations derived from the backcross of a CMS-S maintaining to with eight hybrids with partial fertile pollens were used to verify the function of two yield-related gene APO1 s and to map the genetic loci for fertility restoration to CMS-S. Main results are as follows:1. In this study, two homologs of Os APO1, Zm APO1-6 and Zm APO1-9, were cloned in maize. Zm APO1-6 was located on chromosome 6, and the physical location is between 93,947,173~93,948,969. Zm APO1-9 was located on chromosome 9, and the physical location is between 109,759,365~109,761,167. Both of them share a F-box domain and have more than 83% amino acid identity with Os APO1. RT-PCR analysis revealed that they expressed mainly in stem apex, ears, and tassels. Association mapping was then conducted using about 200 testcross hybrids of a CMS line with diverse inbreds. A total of 14 and 8 significant loci for five yield-related traits were identified, and the loci in Zm APO1-6 were mainly related to plant height and stem diameter, while those in Zm APO1-9 were mainly related to kernel weight. The results of this study implied that these two homologs might be related to yield-related traits in maize, and would facilitate further studies on their detailed functions.2. Based on our genome-wide association study(GWAS) on fertility restoration to CMS-S of maize,testcross hybrids with partial pollen fertility and carrying favourable alleles at the loci significantly associated with pollen fertility were selected and backcrossed with the CMS-S maintainer, N-Mo17rf3rf3 to construct BC1 populations for mapping. Distribution of pollen fertility in the eight BC1 populations showed two or more peaks, suggesting fertility restoration in these populations might be controlled by one or more restoration genes. With the information of the positions of these significant SNPs, 109 SSR markers were selected to genotype the populations. A total of nine QTLs were identified, and individual QTL explained 10.7%~53.3% of phenotypic variation.In total, two homologs of rice Os APO1 encoding proteins with F-box domain were found to be associated with yield and yield-related traits in maize through association analysis. In addition, several genetic loci for fertility restoration of CMS-S with relatively small effects were verified. Results in this study provide useful information for further study on the function of F-box genes and cloning of fertility restorations genes of CMS-S. Meanwhile these results would also facilitate genetic improvement of yield and the application of CMS-S in hybrid of maize production. |
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