Expression of meadowfoam Des5 and FAE1 genes in yeast and in transgenic soybean somatic embryos, and their roles in fatty acid modification

Abstract

Meadowfoam ( Limnanthes spp.) species are unique in that their seeds are rich in the unusual fatty acids Δ 5-eicosenoic acid (C20:1 Δ5) and the diene, C22:2 Δ5, Δ13. Previously the cloning of Δ 5 desaturase ( Des5) and fatty acid elongase 1 ( FAE1) meadowfoam genes and their expression in soybean were reported. Here, we present the first successful expression of the Limnanthes Des5 in yeast, resulting in the desaturation of C16:0, C18:0 and C20:0 to their corresponding cis Δ 5 isomers. In soybean ( Glycine max L.), Limnanthes Des5/FAE1 double transformant somatic embryos fed with radiolabeled C14:0 or C16:0 could elongate these substrates to C18:0, C20:0 and C22:0 and C24:0. However, radiolabeled C18:1 Δ9 or C20:1 Δ11 were not elongated to their respective monounsaturated very long-chain products, confirming that the cloned Limnanthes FAE1 homolog gene product was specific for elongating saturated fatty acids. To understand better the biosynthetic pathway for C22:2 Δ5, Δ13, soybean somatic embryos transformed with the Des5 cDNA were fed in culture with 〚1- 14C〛C 22:1 Δ13 fatty acid, which resulted in the biosynthesis of 〚1- 14C〛-labeled C22:2 Δ5, Δ13. Cell-free preparations enriched with detergent-solubilized Δ 5 desaturase activity extracted from both developing meadowfoam seeds and from Des5 transgenic soybean embryos, produced 14C-22:2 Δ5, Δ13 when supplied with 〚1- 14C〛 C22:1-CoA. Thus, both the in vivo and in vitro experiments showed that the biosynthesis of C22:2 Δ5, Δ13 can occur in somatic soybean embryos transformed with the Limnanthes Des5 cDNA, and confirmed that the pathway for C22:2 biosynthesis in meadowfoam involves further desaturation of erucoyl-CoA by a Δ 5-regiospecific desaturase.