Cahoon Edgar B, Kinney Anthony J
United States Department of Agriculture-Agricultural Research Service, Plant Genetics Research Unit, Donald Danforth Plant Science Center, 975 N. Warson Road, St. Louis, MO 63132 , USA.
J Biol Chem. 2004 Mar 26;279(13):12495-502. doi: 10.1074/jbc.M314329200. Epub 2004 Jan 12.
Dimorphecolic acid (9-OH-18:2Delta(10)(trans)(,12)(trans)) is the major fatty acid of seeds of Dimorphotheca species. This fatty acid contains structural features that are not typically found in plant fatty acids, including a C-9 hydroxyl group, Delta(10),Delta(12)-conjugated double bonds, and trans-Delta(12) unsaturation. Expressed sequence tag analysis was conducted to determine the biosynthetic origin of dimorphecolic acid. cDNAs for two divergent forms of Delta(12)-oleic acid desaturase, designated DsFAD2-1 and Ds-FAD2-2, were identified among expressed sequence tags generated from developing Dimorphotheca sinuata seeds. Expression of DsFAD2-1 in Saccharomyces cerevisiae and soybean somatic embryos resulted in the accumulation of the trans-Delta(12) isomer of linoleic acid (18: 2Delta(9)(cis)(,12)(trans)) rather than the more typical cis-Delta(12) isomer. When co-expressed with DsFAD2-1 in soybean embryos or yeast, DsFAD2-2 converted 18:2Delta(9)(cis)(,12)(trans) into dimorphecolic acid. When DsFAD2-2 was expressed alone in soybean embryos or together with a typical cis-Delta(12)-oleic acid desaturase in yeast, trace amounts of the cis-Delta(12) isomer of dimorphecolic acid (9-OH-18:2Delta(10)(trans,)(12)(cis)) were formed from DsFAD2-2 activity with cis-Delta(12)-linoleic acid [corrected]. These results indicate that DsFAD2-2 catalyzes the conversion of the Delta(9) double bond of linoleic acid into a C-9 hydroxyl group and Delta(10)(trans) double bond and displays a substrate preference for the trans-Delta(12), rather than the cis-Delta(12), isomer of linoleic acid. Overall these data are consistent with a biosynthetic pathway of dimorphecolic acid involving the concerted activities of DsFAD2-1 and DsFAD2-2. The evolution of two divergent Delta(12)-oleic acid desaturases for the biosynthesis of an unusual fatty acid is unprecedented in plants.
异株叶草酸（9-羟基-18:2Δ(10)(反式),(12)(反式)）是异株叶属植物种子中的主要脂肪酸。这种脂肪酸含有一些在植物脂肪酸中不常见的结构特征，包括一个C-9羟基、Δ(10),Δ(12)-共轭双键和反式-Δ(12)不饱和键。进行了表达序列标签分析以确定异株叶草酸的生物合成起源。在从发育中的异株叶种子产生的表达序列标签中鉴定出了两种不同形式的Δ(12)-油酸去饱和酶的cDNA，分别命名为DsFAD2-1和Ds-FAD2-2。DsFAD2-1在酿酒酵母和大豆体细胞胚中的表达导致了亚油酸反式-Δ(12)异构体（18:2Δ(9)(顺式),(12)(反式)）的积累，而不是更典型的顺式-Δ(12)异构体。当与DsFAD2-1在大豆胚或酵母中共表达时，DsFAD2-2将18:2Δ(9)(顺式),(12)(反式)转化为异株叶草酸。当DsFAD2-2单独在大豆胚中表达或与酵母中的典型顺式-Δ(12)-油酸去饱和酶一起表达时，DsFAD2-2与顺式-Δ(12)-亚油酸的活性形成了微量的异株叶草酸顺式-Δ(12)异构体（9-羟基-18:2Δ(10)(反式,)(12)(顺式)）[已校正]。这些结果表明，DsFAD2-2催化亚油酸的Δ(9)双键转化为C-9羟基和Δ(10)(反式)双键，并且对亚油酸的反式-Δ(12)异构体而非顺式-Δ(12)异构体表现出底物偏好。总体而言，这些数据与涉及DsFAD2-1和DsFAD2-2协同活性的异株叶草酸生物合成途径一致。植物中为生物合成一种不寻常脂肪酸而进化出两种不同的Δ(12)-油酸去饱和酶是前所未有的。
