Can E. Coli β-Hydroxydecanoyl-ACP Dehydrase and β-Keto-Acyl-ACP Synthase I Interact with Brassica Napus Fatty Acid Synthase to Alter Oil Seed Composition?

Abstract

A key difference between bacterial and plant fatty acid biosynthesis is the origin of monounsaturated fatty acids. In plants elongation of the fatty acid occurs before the introduction of double bonds by desaturases. In bacteria a double bond can be introduced during elongation at an acyl chain length of C10. That is, the FAS intermediate β-hydroxydecanoyl-ACP is used as a substrate for a specialized dehydrase, β-hydroxydecanoyl-ACP dehydrase (HDD, encoded by fabA). In addition to dehydrase activity, HDD isomerizes the trans β-γ double bond to the adjacent position giving a cis α-β double bond. The latter is maintained while the fatty acid is elongated to the bacterial products, palmitoleic (C16:1 Δ9) and cis-vaccenic (C18:1 Δ11) acid. Can this pathway for bacterial unsaturated fatty acid synthesis be engineered into the seeds of Brassica napus? This would result in the appearance or elevation of palmitoleic and cis-vaccenic acid in the transgenic plants. It has been reported that the introduction of HDD into plants has no effect on lipid composition (Saito et al., 1995; Verwoert et al., 1995), however, it was not known whether the plant KASes were able to elongate the bacterial unsaturated fatty acid intermediates. In bacteria this elongation is carried out by KAS I (encoded by fabB) which is able to use both unsaturated and saturated fatty acids as substrates. We have therefore introduced both the fabA and fabB genes into B. napus to see if the bacterial fatty acids can then be synthesized.