Desaturation of oxygenated fatty acids in Lesquerella and other oil seeds

Abstract

Species of the genus Lesquerella, within the Brassicaceae family, have seed oils containing hydroxy fatty acids. In most Lesquerella species, either lesquerolic (14-hydroxy-eicosa-11-enoic), auricolic (14-hydroxy-eicosa-11,17-dienoic) or densipolic (12-hydroxy-octadeca-9,15-dienoic) acid dominates in the seed oils. Incubations of developing seed from Lesquerella species with 1-14C-fatty acids were conducted in order to study the biosynthetic pathways of these hydroxylated fatty acids. [14C]Oleic (octadeca-9-enoic) acid, but not [14C]linoleic (octadeca-9,12-dienoic) acid, was converted into the hydroxy fatty acid, ricinoleic (12-hydroxy-octadeca-9-enoic) acid, which was rapidly desaturated to densipolic (12-hydroxy-octadeca-9,15-dienoic) acid. In addition, [14C] ricinoleic acid added to Lesquerella seeds was efficiently desaturated at the Δ15 carbon. A pathway for the biosynthesis of the various hydroxylated fatty acids in Lesquerella seeds is proposed. The demonstration of desaturation at position Δ15 of a fatty acid with a hydroxy group at position Δ12 in Lesquerella prompted a comparison of the substrate recognition of the desaturases from Lesquerella and linseed. It was demonstrated that developing linseed also was able to desaturate ricinoleate at position Δ15 into densipolic acid. In addition, the linseed Δ15 desaturase was able to desaturate vernolic (12,13-epoxy-octadeca-9-enoic) acid and safflower microsomal Δ12 desaturase was able to desaturate 9-hydroxy-stearate. Thus, hydroxy and epoxy groups may substitute for double bonds in substrate recognition for oil-seed Δ12 and Δ15 desaturases.