Expression of a borage desaturase cDNA containing an N-terminal cytochrome b(5) domain results in the accumulation of high levels of Δ(6)-desaturated fatty acids in transgenic tobacco

γ-Linolenic acid (GLA; C18:3 Δ(6,9,12)) is a component of the seed oils of evening primrose (Oenothera spp.), borage (Borago officinalis L.), and some other plants. It is widely used as a dietary supplement and for treatment of various medical conditions. GLA is synthesized by a Δ(6)-fatty acid desaturase using linoleic acid (C18:2 Δ(9,12)) as a substrate. To enable the production of GLA in conventional oilseeds, we have isolated a cDNA encoding the Δ(6)-fatty acid desaturase from developing seeds of borage and confirmed its function by expression in transgenic tobacco plants. Analysis of leaf lipids from a transformed plant demonstrated the accumulation of GLA and octadecatetraenoic acid (C18:4 Δ(6,9,12,15)) to levels of 13.2% and 9.6% of the total fatty acids, respectively. The borage Δ(6)-fatty acid desaturase differs from other desaturase enzymes, characterized from higher plants previously, by the presence of an N-terminal domain related to cytochrome b(5).