| Erucic acid is a kind of long chain fatty acids with 22 carbons of little nutrition, which is hard to digest. Therefore, low erucic acid content is considered to be an important indicator of quality in rapeseed oil. The fatty acid elongase 1 (FAE1) gene is the key gene in the erucic acid biosynthesis. The complete coding sequences of the FAE1 gene had been isolated from many plants, such as Arabidopsis, Brassica napus and B. juncea. Meanwhile the transcription of FAE1 had been studied in B. napus. But little related study was reported in B. rapa. China is the birthplace of B. rapa, which contains excellent resources with abundant diversity, Based on this,we can isolate new genetic sources of low erucic acid and study the FAE1 in B. rapa, which will enrich genetic sources and promote the capability of independent innovation in quality improvement. In this study, we detected and analyzed the erucic acid content of different B. rapa accessions and their distribution. Then FAE1 gene and its promoter were cloned, and the transcription of two accessions was analyzed. The main results are as follows:1. Erucic acid content of 47.14 % accessions of B. rapa were between 30 %~40 %, We found zero-erucic acid content samples in"Sanjiecaizi". The results indicated that it was likely to get the zero-erucic acid varieties by continuous purification by generations.2. FAE1 genes of 24 varieties with erucic acid content from 0 %~55 % were cloned and the sequences were analyzed. 26 SNPs were found, 17 of which were single-base mutation in individuals, and 9 SNPs of them were widespread variations. But none of the SNPs was associated with erucic acid content. 26 SNPs led to 13 amino acid variations. However, none was associated with erucic acid content. In this study, we found and proved that the low erucic acid of B. rapa were not caused by FAE1 coding sequence. Phylogenetic analysis showed that sanjiecaizi had obvious genetic relationship with B. rapa in China, however, far from HJa family. There were obvious boundaries in Brassica rapa, Brassica oleracea and Brassica napus, which proved that the gene of low erucic acid did not come from the parents of the AA, but the evolutionary process.3. Transcription analysis showed that there was significant difference between low erucic acid content varieties and high erucic acid content varieties with the same FAE1 sequence in transcription levels, high erucic acid varieties reached peak in 25 days after pollination, while low erucic acid varieties in 20, but only 18.7 % of high erucic acid varieties.4. Using primer pair pF/p712R, we cloned 680 bp of FAE1 promoter from Nanhualinggongdacaizi, and 637 bp from Sanjiecaizi and HJA96337. Clones from the three varieties using primer pair p987F/p primers were all 448 bp. There were only three SNPs in FAE1 promoter between domestic and foreign varieties. 19 SNPs and 43 bp deletion between the high and low erucic acid content varieties, which caused changes and loss in important motif, including an enhancer GACG motifs (GCN4 motif), a g-box, and a recognition sites of RNA polymerase II, TATA-box.
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