Production of fatty acid components of meadowfoam oil in somatic soybean embryos

The seed oil of meadowfoam (Limnanthes alba) and other Limnanthes spp. is e nriched in the unusual fatty acid Delta(5)-eciosenoic acid (20:1 Delta(5)). This fatty acid has physical and chemical properties that make the seed oi l of these plants useful for a number of industrial applications. An expres sed sequence tag approach was used to identify cDNAs for enzymes involved i n the biosynthesis of 20:1 Delta(5)). By random sequencing of a library pre pared from developing Limnanthes douglasii seeds, a class of cDNAs was iden tified that encode a homolog of acyl-coenzyme A (CoA) desaturases found in animals, fungi, and cyanobacteria. Expression of a cDNA for the L. douglasi i acyl-CoA desaturase homolog in somatic soybean (Glycine max) embryos behi nd a strong seed-specific promoter resulted in the accumulation of Delta(5) -hexadecenoic acid to amounts of 2% to 3% (w/w) of the total fatty acids of single embryos. Delta(5)-Octadecenoic acid and 20:1 Delta(5) also composed <1% (w/w) each of the total fatty acids of these embryos. In addition, cDN As were identified from the L. douglasii expressed sequence tags that encod e a homolog of fatty acid elongase 1 (FAE1), a beta-ketoacyl-CoA synthase t hat catalyzes the initial step of very long-chain fatty acid synthesis. Exp ression of the L. douglassi FAE1 homolog in somatic soybean embryos was acc ompanied by the accumulation of C-20 and C-22 fatty acids, principally as e icosanoic acid, to amounts of 18% (w/w) of the total fatty acids of single embryos. To partially reconstruct the biosynthetic pathway of 20:1 Delta(5) in transgenic plant tissues, cDNAs for the L. douglasii acyl-CoA desaturas e and FAE1 were co-expressed in somatic soybean embryos. In the resulting t ransgenic embryos, 20:1 Delta(5) and Delta(5)-docosenoic acid composed up t o 12% of the total fatty acids.