Production of Fatty Acid Components of Meadowfoam Oil in Somatic Soybean Embryos

The seed oil of meadowfoam (Limnanthes alba) and other Limnanthes spp. is enriched in the unusual fatty acid Δ(5)-eicosenoic acid (20:1Δ(5)). This fatty acid has physical and chemical properties that make the seed oil of these plants useful for a number of industrial applications. An expressed sequence tag approach was used to identify cDNAs for enzymes involved in the biosynthesis of 20:1Δ(5)). By random sequencing of a library prepared from developing Limnanthes douglasii seeds, a class of cDNAs was identified that encode a homolog of acyl-coenzyme A (CoA) desaturases found in animals, fungi, and cyanobacteria. Expression of a cDNA for the L. douglasii acyl-CoA desaturase homolog in somatic soybean (Glycine max) embryos behind a strong seed-specific promoter resulted in the accumulation of Δ(5)-hexadecenoic acid to amounts of 2% to 3% (w/w) of the total fatty acids of single embryos. Δ(5)-Octadecenoic acid and 20:1Δ(5) also composed <1% (w/w) each of the total fatty acids of these embryos. In addition, cDNAs were identified from the L. douglasii expressed sequence tags that encode a homolog of fatty acid elongase 1 (FAE1), a β-ketoacyl-CoA synthase that catalyzes the initial step of very long-chain fatty acid synthesis. Expression of the L. douglassi FAE1 homolog in somatic soybean embryos was accompanied by the accumulation of C(20) and C(22) fatty acids, principally as eicosanoic acid, to amounts of 18% (w/w) of the total fatty acids of single embryos. To partially reconstruct the biosynthetic pathway of 20:1Δ(5) in transgenic plant tissues, cDNAs for the L. douglasii acyl-CoA desaturase and FAE1 were co-expressed in somatic soybean embryos. In the resulting transgenic embryos, 20:1Δ(5) and Δ(5)-docosenoic acid composed up to 12% of the total fatty acids.