Genes mapping of tassel branch number in maize based on mixed-pool sequencing and genetic mapping

【Objective】The purpose of the study was to construct the extreme mixing pool and molecular genetic map of maize tassel branch number，and to perform QTL mapping of tassel branch number，so as to provide a theoretical reference for studying the development mechanism of maize tassel branch number and breeding varieties with less tassel branch number.【Method】Firstly，an F₂ population was developed by using an inbred line SNM131 with fewer tassel branches and an inbred line HY813 with more tassel branches. The number of tassel branches per plant in the population was counted and its genetic model was analyzed. Secondly，33 plants with fewer tassel branches and 38 plants with more tassel branches were selected from the F₂ population to construct mixed pools. The whole genome re-sequencing of 30×， 17× and 28× coverage was carried out on the two parents and two offspring mixed pools，respectively. The sequencing data were subjected to association analysis to determine the mapped region of tassel branch number trait. Additionally， single nucleotide polymorphism（SNP）marker typing was performed on 276 individuals of F₂ population with 10K chip. The data obtained were utilized to construct genetic linkage map，and QTL mapping was carried out in combination with phenotypic data of tassel branch number and genomic composite interval mapping（GCIM）. Finally，the candidate gene determining tassel branch number was predicted based on the gene annotation information on the physical section of the B73 reference genome corresponding to the mapped region.【Result】According to statistics，the average number of tassel branches of F₂ population was 7.6，indicating that the number of tassel branches of F₂ population was generally biased towards the female parent SNM131，primarily exhibiting fewer tassel branches. A total of 1812886 single nucleotide polymorphism（SNP）markers and 24714 insertion/deletion（InDel）markers were obtained by genome-wide re-sequencing， and bulked segregant analysis（BSA）of tassel branch number traits was conducted，resulting in the identification of six significant associated regions distributed across maize chromosomes 5，8，and 10. Among them，an associated region with the highest peak value on chromosome 10（physical location 127.61-129.46 Mb ）was judged to be the main locus controlling the number of tassel branches. Besides，a genetic map comprising 2944 SNP markers with a total distance of 3684.3 cM was constructed. Based on geneic linkage map，five QTL were mapped on chromosomes 1，4，6 and 10. Each QTL explained 1.9%-9.9% of the phenotypic variation. The major QTL was mapped in a physical interval of 0.56 Mb （127.81-128.37 Mb）in chromosome 10，which contained 15 candidate genes with medium and high functional mutation sites. The TBN-S gene was related to the development of tassel branch number.【Conclusion】Through field phenotypic identification，genetic map construction and SPN marker mapping，the major QTL controlling the tassel branch number in maize is mapped within a range of approximately 0.56 Mb on the short arm of chromosome 10，which contains 15 genes with medium and high mutation. TBN-S gene is predicted as a candidate gene