Study On The Expressional Pattern And Expression Quantitative Trait Loci Of Key Genes In Flavonoid Biosynthesis Pathway Between Yellow And Black Rapeseed In Brassica Napus L.

The seed coats of rapeseed are rich in polyphenols and fat-soluble pigments, and greatly affect the quality and the meal feeding value of rapeseed. In the same background, previously studies have demonstrated that yellow rapeseed seed has thinner seed coat, higher protein and seed oil content, lower seed coat pigments and toxic materials or antinutritives than black seed varieties. Therefore, development of yellow-seeded B. napus lines and cultivars is one of the most important breeding objectives in rapeseed. So far, more than20gene family members involved in the rapeseed pigments synthesis have been cloned in our previously works in Rapeseed Technology Research Center, Chongqing, and one major QTL for the seed coat colour was detected on the chromosome A09(BnSCA09) in different environments. However, there are still many research works for determining the candidate genes of seed coat colour and revealing the molecular mechanism between the downstream regulatory network and formation of seed coat colour in B. napus.In this research, firstly to definite the expression pattern of ninteen genes of flavonoid pathway in B. napus, we systematic analysis the expression characterization of these genes in the different tissues and organs using the real-time quantitative PCR (qRT-PCR), origined from three different genetic background of the yellow-and black-seeded B. napus. Another, to determine the chromosomal location and upstream regulatory network of these gene families, their expression levels of seeds of30days after flowering in RIL population (GH06xZhongyou821) were detected. Regarding as quantitative traits, the transcript levels of the flavonoid biosynthesis genes families were examined by QTL mapping method for eQTL detection. The main results were as follows:1. Expression characteristics of genes for flavonoid biosynthesis pathway in different genetic sources of yellow-and black-seeded B. napusIn this research, quantitative real-time PCR analysis revealed significant differences and expression pattern of nineteen genes of flavonoid pathway in root, stem, leaf, buds, flower, silique pericarp and five different stage of seeds (10d after flowering,10DAF;20,30,40and50DAF) in yellow and black rapeseed, which have different genetic sources.The results showed that BnTT3, BnTT18, BnBAN, BnTT12, BnTT19, BnTT10, BnAHA10, BnTT2, BnTT8, BnTT16, BnTTG2and BnTT1were preferentially expressed during the seed development, and BnPAPl was specifically expressed in flower. However, BnTT4, BnTT5, BnTT6, BnTT1, BnTTG1and BnTTl5could be detected in different tissues or organs of B. napus. Another, fourteen genes showed significant differences during the seed development, and they had the similar expression pattern among the yellow-and black-seeded B. napus, respectively, exception for the BnTT5, BnTT7, BnTT10, BnTTGl and BnPAP1. The results indicated that flavonoids were synthesized by the same biosynthesis pathway, but showed significant differences only on the rate of synthesis between the yellow-and black-seeded B. napus. These results showed that the background of B. napus have few or no effects on the expression pattern of genes involved in the flavonoid patyway. Moreover, these genes were mainly showed significant differences during the middle to late stages of seed between the yellow-and black-seeded, playing importance roles in the formation of different seed coat colour in B. napus. Hence, the metabolic mechanisms of seed coat colour in B. napus is more complex than that of the Arabidopsis, and inhibiting single or few genes that is difficult to improve the yellow seed traits.2. Expression quantitative trait loci (eQTL) for flavonoid pathway genes in B. napusUsing the composite interval mapping method (CIM) and software Windows QTL Cartographer2.5, we performed an eQTL analysis of94recombinant inbred lines (RILs) from a cross between the female parent GH06and male parent ZY821, using the transcript-level variation in seeds of30days after flower (DAF). A total of seventy-five eQTL for nineteen flavonoid biosynthesis pathway genes were detected and distributed among15different linkage groups, and the average eQTL loci among each gene was ranged from3to5, explaining4.11%to53.11%of phenotypic variation. Another,4eQTL hotspots including30eQTL loci for13genes were detected on chromosome A03, A09and C08, indicating that there may be an upstream regulatory gene in the eQTL hotspots region. Moreover, on chromosome A09, two eQTL hotspots were identified up-and down-stream of the major QTL region (BnSCA09) controlling yellow-seeded trait of B. napus, and the eQTL hotspots on C08showed the same overlapping with seed coat colour and pigments, implying that seed coat colour and pigments might be directly involved in the formation of seed coat colour and controlled by the up-stream gene in B. napus. Besides, we found that the eQTL loci could be detected on different linkage groups, caused that B. napus was allotetraploid, and there were many copies for one gene. These results would be help for understanding the mechanism of regulatory of seed coat colour, and lay the foundation for selecting candidate gene of seed coat colour in B. napus.