The contribution of variations in coding regions or promoters to the changes in FAE1 expression levels have be quantified and compared in parallel by specifically designed swapping constructs. FATTY ACID ELONGATION1 (FAE1) is a key gene in control of erucic acid synthesis in plant seeds. The expression of FAE1 genes in Brassica oleracea and Capsella rubella, representatives of high and low erucic acid species, respectively, was characterized to provide insight into the regulation of very long-chain fatty-acid biosynthesis in seeds. Virtually, no methylation was detected either in B. oleracea or in C. rubella, suggesting that modification of promoter methylation might not be a predominant mechanism. Swapping constructs were specifically designed to quantify and compare the contribution of variations in coding regions or promoters to the changes in FAE1 expression levels in parallel. A significantly higher fold change in erucic acid content was observed when swapping coding regions rather than when swapping promoters, indicating that the coding region is a major determinant of the catalytic power of β-ketoacyl-CoA synthase proteins. Common motifs have been proposed as essential for the preservation of basic gene expression patterns, such as seed-specific expression. However, the occurrence of variation in common cis-elements or the presence of species-specific cis-elements might be plausible mechanisms for changes in the expression levels in different organisms. In addition, conflicting observations in previous reports associated with FAE1 expression are discussed, and we suggest that caution should be taken when selecting a plant transformation vector and in interpreting the results obtained from vectors carrying the CaMV 35S promoter.
Keywords: Erucic acid; Expression regulation; FATTY ACID ELONGATION1; Swapping.