Characterization and functional analysis of a plastidial FAD6 gene and its promoter in the mesocarp of oil palm (Elaeis guineensis)

Oil palm (Elaeis guineensis Jacq.) is one of the most important oil crops in the tropics with special fatty acid compositions. In this paper, a cDNA sequence putatively encoding the plastidial ω6 fatty acid desaturase (FAD) which plays a key role in the linoleic acid biosynthesis, designated EgFAD6, was isolated from the mesocarp of oil palm. Sequence analysis indicated that it had an open reading frame (ORF) of 1320 base pairs (bp) encoding 349 amino acids (aa) of 51 KDa. The real-time fluorescent quantitative PCR results indicated that EgFAD6 mRNA exhibited an extremely high expression level in the mature leaves, and it showed quite flat during the mesocarp ripening with a slight increase at the phase 2. The heterologous expression of EgFAD6 in yeast accumulated a considerable amount of linoleic acid, while no significant difference in other fatty acids when compared with the control pYES2. Furthermore, the promoter of EgFAD6 (proEgFAD6) with 1474 bp in length was isolated and used for functional analysis. The bioinformatics analysis indicated proEgFAD6 contains several potential cis-acting elements, such as light and hormone-responsive elements. Expression analysis in transgenic Arabidopsis revealed that proEgFAD6 could drive β-glucuronidase (GUS) reporter gene express in the leaf, silique coat, stem and flower. These results revealed the function of EgFAD6 and the feature of its promoter, which will be useful for understanding the function and regulation mechanism of plastidial linoleic acid synthesis in other tropical palm plants.