Fine Mapping Of Thousand Seed Weight QTL TSWA7b And Indentification Of Candidate Gene In Brassica Napus L.

Oilseed rape is one of the most important oil crops in the world,and its high yield is the primary goal for genetic breeding.Seed size or weight is the key component of yield traits in Brassica napus L.and it directly affacts the yield of rapeseed.Thousand seed weight trait is a typical quantitative trait.At present,although there are a large number of grain weight QTL localization,but most of the QTLs have not been cloned,and it’s regulatory mechanism is still unclear.In previous studies,the QTL TSWA7b on A7 chromosome has carried out the preliminary mapping and constructed the near isogenic lines（NIL）.Based on the results,we further fine mapped the TSWA7b and screen the candidate genes.The main results are as follows:1.Construction of near isogenic lines at TSWA7b loci:Based on pre-mapping results and constructed BCsF1and BC6F1 NIL,we choose heterozygous plant in the QTL TSWA7b,backcross with DH22 creating the BC6F1 and BC7F1 high generation materials.Then we used 12 cover the QTL region markers to analysis the genotype constructing the BC6F1（n = 45）and BC7F,（n ＝ 48）nearly isogenic lines materials.2.Construction of genetic linkage map at TSWA7b loci:We use the newly developed InDel markers in QTL region and two random mapping population BC3F2 generation（n=192）and BC6F2（n=239）to analysis their genotypes to construct the partial genetic linkage map.In the BC3F2 generation（n=192）random population,a total of 16 dominant markers were analyzed,the total length of the map was 12.5cM,the minimum distance between the markers was 0.3cM,and the average distance was 0.78cM.In the BC6F2 generation（n=23 9）random population,a total of 20 dominant markers were analyzed,the total length of the map was 12.3cM,the minimum distance between the markers was 0.3cM,and the average distance was 0.61cM.The relative positions of the same molecular markers in the two genetic linkage maps were basically consistent.According to BC3F2、BC4F3 and BC3F4 groups in the selection of the QTL loci of the exchange of plant（n=107）genotype and phenotype mapping found that the control of 1000 grain weight of the gene is located between makers BnA7₆7 and BnA7₅3.3.According to the physical location information of the genetic linkage map which is constructed according to the precise location results,the candidate segment is located between BnA7-53 and BnA7-67.There are 24 predicted genes in the QTL segment.Sequence analysis of the parental alleles revealed that there are 20 genes in the CDS sequence have the base mutations,and 17 genes resulted in the variation of amino acids.Based on the annotation function of Arabidopsis thaliana,we identified a protein relates to auxin as a candidate gene for the QTL.The work that fine mapping and candidate gene identification of A7 locus,helping to analysis molecular and genetic mechanism of kernel weight,increasing rape yield,providing the basis for the evolution of the rape.