title: Dimorphecolic acid is synthesized by the coordinate activities of two divergent Delta12-oleic acid desaturases.
abstract: 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.
authors.affiliation: 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. ecahoon@danforthcenter.org
authors.forename: Edgar B
authors.initials: EB
authors.lastname: Cahoon
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Kinney
mesh_terms: D020838:Calendula / Q000378:metabolism*; D002849:Chromatography, Gas; D018076:DNA, Complementary / Q000378:metabolism; D020224:Expressed Sequence Tags; D044943:Fatty Acid Desaturases / Q000737:chemistry*; D005227:Fatty Acids / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D019787:Linoleic Acid / Q000737:chemistry; D044243:Linoleic Acids, Conjugated / Q000096:biosynthesis* / Q000737:chemistry*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D019301:Oleic Acid / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D010802:Phylogeny; D010957:Plasmids / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D012639:Seeds / Q000378:metabolism*; D013025:Glycine max / Q000378:metabolism; D013997:Time Factors
chemical_list: D018076:DNA, Complementary; D005227:Fatty Acids; D044243:Linoleic Acids, Conjugated; D010455:Peptides; C024347:9-hydroxy-10,12-octadecadienoic acid; D019301:Oleic Acid; D019787:Linoleic Acid; D044943:Fatty Acid Desaturases; C040448:delta-12 fatty acid desaturase