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

Abstract

The seed oil of meadowfoam (Limnanthes alba) and other Limnanthes spp. is enriched in the unusual fatty acid ⌬ 5 -eicosenoic acid (20:1⌬ 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 20:1⌬ 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 ⌬ 5 -hexadecenoic acid to amounts of 2% to 3% (w/w) of the total fatty acids of single embryos. ⌬ 5 -Octadecenoic acid and 20:1⌬ 5 also composed Ͻ1% (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 ␤-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 20:1⌬ 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, 20:1⌬ 5 and ⌬ 5 -docosenoic acid composed up to 12% of the total fatty acids.

Functional Analysis of a β-Ketoacyl-CoA Synthase Gene,MpFAE2, by Gene Silencing in the LiverwortMarchantia polymorphaL.

“…2) the CUT1 gene, 4) the S. chinensis KCS gene, 6) and the L. douglasii KCS gene. 8) In M. polymorpha neither MpFAE2 gene silencing nor overexpression in‰uenced the amount of lignoceric acid (24:0), implying that the fatty acid chain elongation from 22:0 to 24:0 is catalyzed by another KCS, which is tightly regulated in M. polymorpha. The involved enzymes and regulatory mechanism for the elongation of 22:0 to 24:0 in M. polymorpha are yet to be investigated.…”

Involvement of Arabidopsis ACYL-COENZYME A DESATURASE-LIKE2 (At2g31360) in the Biosynthesis of the Very-Long-Chain Monounsaturated Fatty Acid Components of Membrane Lipids

“…The lipid substrate of this desaturase was not determined and the cDNA appeared to encode an enzyme with a plastid transit peptide. The D5 desaturase catalyzing the synthesis of 20:1D5 in the seeds of Limnanthes alba is also an ADS homolog (Cahoon et al, 2000). The substrate for this reaction is thought to be the 20:0-CoA thioester (Pollard and Stumpf, 1980;Moreau et al, 1981).…”

Characterization of Enzymes Involved in Fatty Acid Elongation

“…Mutations in FAE1 resulted in reduced levels of seed VLCFAs [67,68], and a deficiency in acyl chain elongation activities toward C 18 and C 20 FAs [69]. FAE1 homologs were identified in several plants, Brassica oleracea [70], Brassica campestris [71], Brassica oleacea [71], Simmondsia chinensis [72], Lesquerella fendleri [73] and Limnanthes alba [74] and also in the green algae, Dunaliella salina [75]. In the Arabidopsis genome, 20 predicted FAE1 homologs were found (Fig.…”