Functional characterization and expression profile of microsomal FAD2 and FAD3 genes involved in linoleic and α-linolenic acid production in Leucas cephalotes

Abstract

The genus Leucas belongs to Lamiaceae, and has attained more attention due to the presence of unusual allenic fatty acids called laballenic and phlomic acid in majority of its species. This genus has been known since traditional medicinal times and has numerous economical, nutritional, and industrial properties. So far genetic, molecular and biochemical analyses of lipid metabolism and fatty acid biosynthetic pathway in Leucas has not been reported. The objective of this study is to identify, isolate, analyze expression profiles, and functionally characterize the membrane-associated desaturases responsible for unsaturated fatty acid accumulation in Leucas cephalotes. Full-length LcFAD2 and LcFAD3 cDNAs were isolated and expressed in Saccharomyces cerevisiae BY4741 for functional characterization. Substrate feeding assay using S. cerevisiae confirmed that the LcFAD2 enzyme catalyzes desaturation of both palmitoleic (16:1∆9) and oleic (18:1∆9) acids to form palmitolinoleic (16:2∆9,12) and linoleic (18:2∆9,12) acids respectively. As a contrast, the heterologous activity of LcFAD2 enzyme in S. cerevisiae led to the synthesis of palmitolinoleic (16:2∆9,12) acid, an unusual fatty acid that is not found naturally in Leucas cephalotes. While the LcFAD3 enzyme catalyzed linoleic acid (18:2∆9,12) into α-linolenic acid (18:3∆9,12,15). Furthermore, transcript abundance of LcFAD2 and LcFAD3 cDNAs were estimated from various plant parts such as roots, shoots, leaves, petals and developing seeds. Our results have shown that the differential transcriptional activity of LcFAD2 and LcFAD3 desaturase genes differs significantly in developing seeds, petals, leaves, stems, and roots of L. cephalotes. Furthermore, for the industrial production of these essential fatty acids, namely, linoleic and α-linolenic acid, FAD2 and FAD3 enzyme activity could be exploited from this upcoming significant oil plant, Leucas cephalotes.