Natural Variation And Genetic Mechanism Of Anthocyanin And Flavonol Glycoside Metabolism In Brassica Rapa

Brassica rapa, comprising a variety of vegetables and oil crops, is one of the most consumedvegetable which plays an important role in people’s daily diets in China and throughout East Asia. Withthe improvement of living standard, people pay more attention to the nutritional qualities of vegetables.Anthocyanins and flavonol glycosides, which are two major groups of flavonoid compounds, performseveral key biological functions in plants as well as play beneficial health roles as potential protectivefactors against cancer and heart disease. Because of the nutritional value and beneficial health effects,vegetables which are rich in these two compounds are increasingly popular and received considerableresearch attention. So it is necessary to characterize the composition and reveal the genetic mechanismof anthocyanins and flavonol glycosides in B. rapa.In this study, the profiles and the contents of anthocyanins and flavonol glycosides were identifiedin the leaves of different accessions to reveal the natural variation of these two metabolites in B. rapa.Anthocyanin and flavonol glycoside biosynthetic genes have been identified by comparative genomicanalysis between B. rapa and Arabidopsis thaliana. QTL mapping analysis was conducted for the genescontrolling anthocyanin biosynthesis in Zicaitai (Brassica rapa L. ssp. chinensis var. purpurea). Amethod combining super-BSA and high throughput re-sequence was used to map the gene for purplepigmentation in leaves of purple pakchoi (Brassica rapa L. ssp. chinensis). The candidate genesinvolved in flavonol glycosides biosynthesis of B. rapa were identified by correlation analysis betweenexpression and metabolic profiling, as well as genome-wide association study (GWAS).The main results of this dissertation are as follows:1. To investigate the metabolic profiles of anthocyanins and flavonol glycosides in the leaves of B.rapa accessions, an analytical method combining UFLC-UV-Q-Trap-MS and UPLC-Q-TOF-MS wasperformed. In total,23anthocyanins were detected and identified in the leaves of Zicaitai, purple turnipand purple pakchoi.17different acylated cyanidin3-di/triglucoside-5-glucosides were detected inZicaitai and purple pakchoi, while six different acylated pelargonidin3-diglucoside-5-glucosides wereidentified in purple turnip.27flavonol glycosides containing15kaempferol glycosides,10quercetinglycosides and two isorhamnetin glycosides were identified in95accessions. The contents of flavonolglycosides were significant difference among the95accessions which accumulated the same27components.2. Comparative genomic analyses between A. thaliana and B. rapa on a genome-wide level wasconducted to elucidate the anthocyanin and flavonol glycosides biosynthetic pathway in B. rapa. In total,we identified73genes in B. rapa as orthologs of41biosynthetic genes in A. thaliana. In B. rapa, theanthocyanin and flavonol glycosides biosynthetic genes have expanded and most genes exist in morethan one copy. The anthocyanin biosynthetic structural genes have expanded through whole genome andtandem duplication in B. rapa. More structural genes located upstream of the anthocyanin biosyntheticpathway have been retained than downstream. More negative regulatory genes have been retained than positive ones in the biosynthetic pathway, which may help us to understand the morphologicalcharacteristics and genetic basis of these two metabolites in B. rapa.3. The expression profile and qPCR analysis showed that the expression levels of late biosyntheticgenes were higher in purple accessions than in green ones, and the negative regulatory genes ofanthocyanin biosynthesis were expressed higher in green accessions. The different expression patternsof BrF3’H between Zicaitai and purple turnip could explain that different kinds of anthocyanins wereidentified in these two purple cultivars. BrFLS1and BrDFR could reveal the metabolic characteristic ofanthocyanins and flavonol glycosides in puple or green accessions.4. To determine the genetic basis controlling anthocyanin accumulation in Zicaitai, we conductedQTL analysis. A major QTL was identified for total anthocyanin content on chromosome A09whichexplained56.7%of phenotypic variation. Two genes, BrEGL3.1and BrEGL3.2, which are syntenicorthologs of AtEGL3, are candidate genes for a key role in the control of anthocyanin accumulation inZicaitai.5. Two DNA pools which contained900green lines and200purple lines from a F2populationcrossed by purple pakchoi and green Caixin were resequenced to map the gene for the purplepigmentation of pakchoi leaves. The selected signal was found in a1.5Mb region at the end ofchromosome A03, and two anthocyanin biosynthetic genes were identified.6. The candidate genes involved in flavonol glycosides biosynthesis of B. rapa were identified bycorrelation analysis between expression and metabolic profiling, as well as genome-wide associationstudy (GWAS), which will promote the cloning and functional analysis of the genes controlling flavonolglycosides accumulation and the understanding of the biological process of flavonol glycosidesbiosynthesis in B. rapa, as well as offer genetic resources and theoretical foundation for thedevelopment of new varieties with enhanced health-promoting properties by molecular breeding.