Biosynthetic origin of conjugated double bonds: production of fatty acid components of high-value drying oils in transgenic soybean embryos

• Published in: Proceedings of the National Academy of Sciences - PNAS 1999-10, Vol.96 (22), p.12935-12940
• Main Authors: Cahoon, E.B, Carlson, T.J, Ripp, K.G, Schweiger, B.J, Cook, G.A, Hall, S.E, Kinney, A.J
• Format: Article
• Language: English
• Subjects: 12-oleic acid desaturase; a-eleostearic acid; a-parinaric acid; alpha-eleostearic acid; alpha-parinaric acid; Amino Acid Sequence; amino acid sequences; Base Sequence; Biological Sciences; Botany; Complementary DNA; Conjugated linoleic acids; D12-oleic acid desaturase; DNA Primers; DNA, Complementary; embryo (plant); Embryos; Enzymes; Esters; Expressed Sequence Tags; Fatty Acid Desaturases - genetics; Fatty acids; Fatty Acids - biosynthesis; Flowers & plants; genbank/af182520; genbank/af182521; gene expression; gene transfer; genetic transformation; Glycine max; Glycine max - embryology; Glycine max - enzymology; Glycine max - metabolism; Impatiens balsamina; Libraries; lipogenesis; long chain fatty acids; messenger RNA; Molecular Sequence Data; molecular weight; Momordica charantia; nucleotide sequences; oleic acid desaturase; Plants, Genetically Modified - embryology; Plants, Genetically Modified - enzymology; Plants, Genetically Modified - metabolism; polyunsaturated fatty acids; Recombinant Proteins - genetics; RNA; Saccharomyces cerevisiae - genetics; seeds; Seeds - enzymology; Sequence Homology, Amino Acid; Soybeans; stearoyl-CoA desaturase; Transgenic plants
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.96.22.12935

Vegetable oils that contain fatty acids with conjugated double bonds, such as tung oil, are valuable drying agents in paints, varnishes, and inks. Although several reaction mechanisms have been proposed, little is known of the biosynthetic origin of conjugated double bonds in plant fatty acids. An expressed sequence tag (EST) approach was undertaken to characterize the enzymatic basis for the formation of the conjugated double bonds of alpha-eleostearic (18:3delta(9cis, 11trans,13trans)) and alpha-parinaric (18:4delta(9cis,11trans,13trans,15cis)) acids. Approximately 3,000 ESTs were generated from cDNA libraries prepared from developing seeds of Momordica charantia and Impatiens balsamina, tissues that accumulate large amounts of alpha-eleostearic and alpha-parinaric adds, respectively. From ESTs of both species, a class of CDNAs encoding a diverged form of the delta(12)-oleic acid desaturase was identified. Expression of full-length cDNAs for the Momordica (MomoFadX) and Impatiens (ImpFadX) enzymes in somatic soybean embryos resulted in the accumulation of alpha-eleostearic and alpha-parinaric acids, neither of which is present in untransformed soybean embryos. alpha-Eleostearic and alpha-parinaric acids together accounted for as much as 17% (wt/wt) of the total fatty acids of embryos expressing MomoFadx. These results demonstrate the ability to produce fatty acid components of high-value drying oils in transgenic plants. These findings also demonstrate a previously uncharacterized activity for delta(12)-oleic acid desaturase-type enzymes that we have termed "conjugase."