Development Of Chromosome Segment Substitution Lines For QTL Analysis Of Important Agronomic Traits And Cloning The White-flowered Gene In Brassica Napus L.

The Brassica family includes many economically important industrial and edible oilseed, vegetable and fodder crop species. Canola or oilseed rape(Brassica napus) has become the world’s third most important oil crop. In order to learn the genetic basis of the important traits in B. napus, a set of Chromosome segment subsitution lines w ere developed to carry out the QTL mapping for yield- and quality-related traits in this reseach. In addition, we used the map-based cloning approach to idenfy the white flower gene- Bna C3.CCD4 in the resynthesized white-flowered rapeseed line No. 2127,which revealed the molecular mechanism of flower color formation and maintenance in Brassica species and uncover the relationship between the flowr color evolution and the plant adaptation, Then the evolution dynamics of C3.CCD4 in the Brassica genomes was also analyzed. The main results were described as follows: 1. Development of chromosome segment substitution lines in rapeseed(Brassica napus L.) using for QTL mapping of yield- and quality-related traitsIn this study, a set of chromosome segment substitution lines(CSSL) were developed using backcross combined to maker-assistant selection with ZY821 as recurrent parent and No.2127 as donor parent. This CSSL population consists of 89 individuals, which were subjected with reduced-representation sequencing. Each lines habours about 3.76 introgressed segments from No.2127 in average. The mean length of these introgressed segments is 21.86 c M, and the CSSLs have the genome proportion of the recurrent parent with an average of 96.24%. All the introgressed segments in this set of CSSLs basically covered the whole genome of Brassica napu L. Three yield-related traits(flowering time, pod length and seed number per pod) and 8 seed quality-related traits(protein content, oil content, erucic acid content, Glucosinolate content, linoleic acid content, oleic acid content and palmitic acid content) were investigated for two years(in 2013 and 2014). All these 11 traits showed continuous distribution and transgressive segregation. Most of them were correlated with each other. Combining the genotype and phenotype of these CSSLs, QTL mapping for these 11 traits was performed and totally 43 QTLwere detected in two environments. Of these QTL, four, three, and six QTL were associated with flowering time, pod length and seed number per pod, respectively; three, three, five, four, three, four, three, and three QTL were associated with protein content, oil content, erucic acid content, glucosinolate content, linoleic acid content, oleic acid content and palmitic acid content, respectively. Twenty-nine of these 43 QTL could be detected in both years. And some QTL for the flowering time on A2, flower color on C3, seed color on C8, high oil content gene on C8 and high Glucosinolate content gene on A9 have been cloned or cloning. 2. Map-basedcloning, functional and evolutionary study of the dominant white-flowered gene in BrassicaThe carotenoids in petals of yellow-flowered rapeseed line ZY821 and white-flowered rapeseed line No.2127 were mainly composed of violaxanthin, 9-cis-violaxanthin and lutein. But the concentration of total and some individual carotenoids was quite different between the yellow and white petals. The concentration of total carotenoid in petals of ZY821 is 43-fold higher than that in petals of No.2127, and the concentration of major carotenoid accounting for 89.0% of the total carotenoids in yellow petals of ZY821, and being 94-fold higher than the concentration in No.2127.The flower colour in B.napus is controlled by a single nuclear gene Bna FC, with white flower dominant over yellow flower. The Bna FC gene was a carotenoid cleavage dioxygenase gene- CCD4, which was identified using association mapping and genetic transformation in B.napus. In white-flowered No.2127 there is a functional Bna C3.CCD4(WT type) whose opening reading frame(ORF) is 1791 bp in length and encodes a putative protein consisting of 597 amino acids. The Bna C3.CCD4 localizing in the plastid was preferentially expressioned in buds and petals and could cleave α- and/or δ-carotene to produce α-ionone, which lead to the flower color change from yellow to white. While in yellow-flowered ZY821, a 7.61 kb CACTA-like transposable element 1(TE1) was located in the ORFs of Bna C3.CCD4 which disrupted the transcription of Bna C3.CCD4 in yellow-flowered rapeseed cultivars. This haplotype of C3.CCD4 with TE1 was designated as M1 type.Five C3.CCD4 haplotypes, including WT type and four variations: M1, 2, 3 and 4 type, were identified in the Brassica species. These variations disrupted the function of C3.CCD4, thus changing petal colour from white to yellow. Some yellow-flowered B. oleracea lines and all yellow-flowered B. napus and B. carinata accessions were homozygous for M1 or M4, suggesting that the insertions of CACTA-like TEs into C3.CCD4 predated allopolyploidization of B. napus and B. carinata. In addition, M2 type and M3 type were specifically found in B. oleracea but not in either B. napus or B. carinata, suggesting that M2 type and M3 type mutations might occur outside of the origination centres of B.napus and B.carinata and not participate in their speciations.