Construction Of SSR-based Genetic Map And QTL Mapping For Oleic Acid Content In Rapeseed (Brassica Napus L.)

Rapeseed (Brassica napus L.) is one of the most important oilseed plants globally. The quality of rapeseed oil is classified by its fatty acid composition. Oleic acid, which is one of the major fatty acids for the rapeseed oil, has several superior features. These features make the high oleic acid breeding a vital breeding goal in rapeseed.QTL mapping for oleic acid content and studies on the major gene FAD2 which controls the oleic acid in Brasscia napus are two essential approachings for the high oleic acid breeding and mechanism research on the oleic acid biosynthesis in rapeseed seeds. In this study, a F2 segregating population, which derived from the hybrid of a zero-ecucic-high-oleic-acid parent HOP and a zero-erucic-low-oleic-acid parent Xiangyou 15, has been constructed for the construction of genetic map and QTL mapping for the oleic acid content in B. napus. Meanwhile, genomic distribution of the FAD2 gene family in B. napus has investigated for revealing the correlation between the FAD2 genes and the oleic acid contents.The following are the major accomplishments and results of this research:1) Constructions of research materials in B. napusFollowing populations have been obtained using spring high-oleic-acid B. napus line HOP and winter low-oleic-acid B.napus varieties Xiangyou 15:(1) the F2 segregating population consists of 189 individuals for the genetic map construction; (2) the BC4F1 generation which the Xiangyou 15 has been used for its recurrent parent; (3) the F4 family which consists 384 lines for the construction of the recombinant inbred lines.2) Construction of SSR based genetic map of B. napusA SSR based genetic map which consists of 342 SSR markers, and with the total length of 1697.1cM long, the average linkage group length of 89.32cM and the interval length of 6.35cM, has been constructed using the 189 F2 segregating population. Comparative mapping between this map and the other reference maps shows a good collinarity, which means this map could be used for further research. Regulations of distribution of the distorted markers have been revealed:(1) The P2 type distorted markers are the superior ones as a whole; (2) concentrated at the end of linkage groups (LG); (3) distorting orientation of the concentrated markers tend to be the same, the isolated distorted markers tend to the F1. 3) Analysis on the fatty acid contents of the F2 population in B. naptlsHalf-seed method and bulk-seed method have been used for the gas chromatogram (GC) analysis on the fatty acid contents of the F2 population in B. napus. High correlations have been found between these two analytic methods, it means these two methods could be verified each other. All of the frequency distributions of the fatty acid contents of the F2 population are normal, and most of the correlations between these major fatty acids are statistically significant.4) QTL mapping of the oleic acid content in B. napusQTL mapping on the oleic acid content was carried out using the SSR genetic map and the oleic acid contents values of 189 half-seed seeds and 156 bulk-seed plant individuals. Two major oleic acid content QTLs altogether have been found on the LGs A5 and C5, respectively. These two QTLs have respectively explained 59% and 16% (half-seed, CIM) variances of the oleic acid content. The QTL on LG A5 is associated with the FAD2 gene, probably as well as the newly found QTL on LG C5.5) Analysis on the FAD2 gene family of B. napus genomeThe FAD2 gene which contains the coding region and about 1000 bps 5' regulatory region has been cloned and sequenced form the genomes of the two parents HOP and Xiangyou 15. The sequences obtained could be classified into four copies which are FAD2-1a, FAD2-1b, FAD2-2 and FAD2-3. OFR analysis suggests three of these four copies could be translated into an intact FAD2 peptide chain which consists of 184 amino acid residues while the FAD2-3 is the exception. Among these three copies, FAD2-1a and FAD2-1b have shown very close homology each other whether the coding region or regulatory region is invested; FAD2-2 shares only 89% homology with FAD2-1a and FAD2-1b while the coding regions are compared, if the comparison is based on the regulatory region, the homology value will reduce to 50%. BLAST analysis and comparison between the FAD2 gene sequences of B. napus, B. rapa and B. oleracea, which obtained in this research or downloaded from the public B. rapa genome database, suggests that the FAD2-1b, FAD2-1a and FAD2-2 are locating in chromosome A5, C5 and C1, respectively.