Genetic Analysis And Fine Mapping Of The Flower Color Gene In Brassica Rapa

Brassica rapa is one of the three rape types in China,and one of the representative species of Brassica.Color of the plant flower is mainly determined by the pigment contained in the petals,B.rapa has yellow flower under natural conditions.In order to analyze the molecular mechanism of the flower color traits of B.rapa,to understand the different regulation mechanism of Brassica family and to reveal the Brassica flower color pattern of evolution,in this study,an F2 population obtained from the cross of the yellow-flowered B.rapa P3246 and the white-flowered B.rapa W01 was used to carry out the primary mapping and fine mapping of the white flower gene.The main results were described as follows:1.Carotenoid composition and content in petals and leavesCarotenoid content was determined by HPLC for leaves and petals of two parent materials P3246 and W01.There was no difference in the composition of carotenoid in the leaves and petals,the content difference was remarkable,especially in the petals.The highest content of carotenoid was violaxanthin and lutein.The content of violaxanthin in P3246 was 3009.86 ?g/g,accounting 86.6% of the total content of carotenoid,the content of violaxanthin in W01 was 242.06 ?g/g,accounting 72.0% of the total content of carotenoid in the petals.The total content of carotenoid in the yellow material was10.3-fold higher than W01.2.Inheritance law of the flower colorA total of 3104 F2 plants were obtained by the cross of yellow-flowered B.rapa P3246?P1?and white-flowered W01?P2?,during flowering time petal color traits were investigated.Of the 3104 individuals of F2 population,783 had white petals and 2321 had yellow petals,the segregation ratio conformed the Mendelian ratio of 3:1 by the chi-square test(X_c²=0.073,X_0.05,1²=3.84,P>0.05).It was confirmed that the white flower was controlled by a single recessive gene.3.Mapping of the flower color geneOne hundred and forty-two InDel markers were screened by the Bulked Segregant Analysis?BSA?,4 InDel markers located on the chromosome A02 were linked to the flower color gene,so the flower color gene was located on the chromosome A02.Using15 polymorphic SSR and InDel markers,flower color gene was primary mapped between markers A02-1142 and A02-1144 by BSA,the genetic distance was 1.5cM.A total of2330 individuals containing 8 representative recombinants and 2322 F2 individuals were selected as the fine mapping population,using 9 polymorphic SNP markers and 1polymorphic InDel marker,the flower color gene was mapped between SNP markers A02_SNP-378 and A02_SNP-1100 with a genetic distance of 0.39 cM,the interval on reference genome is about 162 kb.Marker A02_SNP-389 co-segregated with the flower color gene.4.Candidate genes analysisTwenty-five annotated genes were found on the 162 kb target region of the B.rapa reference genome V1.5,and the 25 genes were analyzed with the homologous Arabidopsis gene sequence to identify the possible candidate gene.