QTL Mapping For Plant Height,The First Branch Height,And Branch Number And Cloning Candidate Genes Related To Plant Height In Brassica Napus L.

Rapeseed(Brassica napus L.) is one of the most important oil crops in China, which provides not only edible vegetable oil for human diets, but also protein-rich feed for animals.The increased yields as well as mechanized production have been the primary task in rapeseed breeding, and furthermore lodging-resistant and mechanized harvestingalso have been the breeding objective.Lots of studies show that plant height, the first branch height and branch number are the indirect determination factors of rape seed yield per plant, moreover, plant height is the key to achieve the breeding goal of lodging-resistant and mechanized harvesting.In this study, RIL from combination of GH06 and P174 were used as target population, and the plant height, the first branch height, and branch number were investigated. A detection and analysis of QTL was performed by the combination of a SNP genetic linkage map which based on the RIL population and phenotypic data from three traits. According to the analysising results, the screening of candidate genes has been completed. The cloning and bioinformatics analysis of plant height candidate gene Bn GA3 from the two parents of the RIL population.Our main results are as follows:1. The investigated results show that all of three traits varied continuously, and transgressive segregation for all the traits was observed in RIL. Correlation analysis showed that the same trait was significantly positively correlated in three years,the correlation coefficient of plant height between 2013 and 2015 was as height as 0.981. Also, there existed correlations among various traits, as the plant height was extremely significantly positively correlated with the first branch height, a high correlation coefficient of 0.468 was found in 2013.The first branch height was extremely significant negative correlation with branch number.The stem fiber composition content of RIL(recombinant inbred line) were predicted with the NIRS models. Correlation analysis in our research found that plant height was extremely significant positively correlated with lignin content in stem.There was also a high correlation between plant height and syringly monomer content with correlation coefficient of 0.322 in 2015.2. We have investigated phenotypic data of three traits of three consecutive years, a total of 68 QTL were found by composite interval mapping. Among these, plant height, the first branch height and branch number have 28, 12, and 28 QTL, respectively. Some QTLcan be found on the same position for three consecutive years, but most of QTL can only be found in one year. In addition, QTL of three traits are spread out pretty evenly among the genome but nonuniform distribution among the linkage groups. There is a pleiotropism or close linkage be found among the three traits.A QTL cluster for plant height, the first branch height and branch number was found in a 20.6 c M region on the C07 linkage group, 17 related QTL had a completely or partially overlap confidence interval. In this region, plant height and the first branch height were characterized by major QTL, and the increasing effective allele was from female parent GH06. However, the branch number had a litte QTL effect.3. A total of 82 candidate genes were found in QTL confidence interval by homologous comparison, among these, 48 genes from 25 QTL of plant height, 5 genes from 3 QTL of the first branch height, and 29 genes from 16 QTL of branch number. The biological function of these candidate genes mainly involved in biosynthesis, metabolism, signal transduction and response of plant hormone. Phenotypic variation explained by the putative QTL varied from 10.16% to 14.95%. Several candidate genes related to GA biosynthesis were detected in the QTL cluster on the C07 linkage group, suggesting that the formation of the QTL region is likely to be related to the biosynthesis gene of GA.4. Bioinformatics assay showed that the Bn GA3 gene structure composed of 6 exons and 5 introns. The Bn GA3 gene encoding protein of two parents composed of 498 and 499 amino acid residues, respectively. Their molecular weight are about 57.02 k D and 56.97 k D respectively and isoelectric points are aound 6.62 and 6.75 respectively.There is adifference of 13 amino acid residues between GH06 and P174, but the hydrophilicity/hydrophobicity, the secondary structure, tertiary structure and structural domains of GH06 deduced protein are little different from P174 deduced protein; the cloning genes main difference between GH06 and P174 was focused on the first intron. Whether this difference is the reason for the formation of the QTL site is to be further studied.