Molecular evidence for blocking erucic acid synthesis in rapeseed (Brassica napus L.) by a two-base-pair deletion in FAE1 (fatty acid elongase 1)

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 1422–1423 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.