DNA sequences of fatty acid elongase 1 genes FAE1.1(EA) and FAE1.2(EC) were isolated and characterized for 30 commercialized low erucic acid rapeseed(LEAR) cultivars in China. Four types of independent mutation leading to low erucic acid trait were found, i.e., a single-base transition(eA1), a two-base deletion(eC2) and four-base deletion(eC4) as well as single-base transition with a four-base deletion(eA*). Three genotypes, i.e., eA1eA1eC2eC2, eA1eA1eC4eC4 and eA*eA*eC4eC4 were responsible for LEA content in storage lipids of different rapeseed cultivars. Most of the LEAR cultivars had a genotype of eA1eA1eC2eC2, which were descended from the first LEAR cultivar, Oro. Yeast expression analysis revealed that two-base-pair(AA) deletion(eC2) at the base sites of 1 422–1 423 in the C genome FAE1 gene resulted in the absence of the condensing enzyme and led to the failure to produce erucic acid. Coexpression of FAE1 and ketoacyl-CoA reductase(KCR) or enoyl-CoA reductase(ECR) was found in high erucic acid rapeseed(HEAR) but not in LEAR(eA1eA1eC2eC2 or eA1eA1eC4eC4). Moreover, KCR and ECR were still coordinately regulated in eA1eA1eC2eC2 or eA1eA1eC4eC4 genotypes, suggesting that the expression of two genes was tightly linked. In addition, specific detection methods were developed by high-resolution melting curve analysis in order to detect eA1 and eC4.
The fatty acid elongase 1 (FAE1) genes of Brassic napus were cloned from two cultivars, i.e. Zhong- shuan No. 9 with low erucic acid content, and Zhongyou 821 with high erucic acid content, using the degenerate PCR primers. The sequence analysis showed that there was no intron within the FAE1 genes. The FAE1 genes from Zhongyou 821 contained a coding sequence of 1521 nucleotides, and those cloned from Zhongshuan No. 9 contained a 1517 bp coding sequence. Alignment of the FAE1 sequences from Brassica rapa, B. oleracea and B. napus detected 31 single nucleotide polymorphic sites (2.03%), which resulted in 7 amino-acid substitutions. Further analysis indicated that 19 SNPs were genome-specific, of which, 95% were synonymous mutations. The nucleotide substitution at po- sition 1217 in the FAE1 genes led to a specific site of restricted cleavage. An AvrII cleavage site was present only in the C genome genes and absent in the A genome FAE1 genes. Digestion profile of the FAE1 sequences from B. rapa, B. oleracea and B. napus produced with AvrII confirmed that the FAE1 genes of B. oleracea origin was recognized and digested, while that of B. rapa origin could not. The results indicated that by AvrII cleavage it was possible to distinguish B. rapa from B. oleracea and be- tween the A and C genome of B. napus. In addition, the FAE1 genes could be used as marker genes to detect the pollen flow of B. napus, thus providing an alternative method for risk assessment of gene flow.
WU YuHua, XIAO Ling, WU Gang & LU ChangMing Oil Crops Research Institute, Chinese Academy of Agricultural Sciences, Wuhan 430062, China
