title: Acyl CoA profiles of transgenic plants that accumulate medium-chain fatty acids indicate inefficient storage lipid synthesis in developing oilseeds.
abstract: Several Brassica napus lines transformed with genes responsible for the synthesis of medium- or long-chain fatty acids were examined to determine limiting factor(s) for the subsequent accumulation of these fatty acids in seed lipids. Examination of a decanoic acid (10:0) accumulating line revealed a disproportionately high concentration of 10:0 CoA during seed development compared to long-chain acyl CoAs isolated from the same tissues, suggesting that poor incorporation of 10:0 CoA into seed lipids limits 10:0 fatty acid accumulation. This relationship was also seen for dodecanoyl (12:0) CoA and fatty acid in a high 12:0 line, but not for octadecanoic (18:0) CoA and fatty acid in a high 18:0 line. Comparison of 10:0 CoA and fatty acid proportions from seeds at different developmental stages for transgenic B. napus and Cuphea hookeriana, the source plant for the medium-chain thioesterase and 3-ketoacyl-ACP synthase transgenes, revealed that C. hookeriana incorporates 10:0 CoA into seed lipids more efficiently than transgenic B. napus. Furthermore, beta-oxidation and glyoxylate cycle activities were not increased above wild type levels during seed development in the 8:0/10:0 line, suggesting that lipid catabolism was not being induced in response to the elevated 10:0 CoA concentrations. Taken together, these data suggest that transgenic plants that are engineered to synthesize medium-chain fatty acids may lack the necessary mechanisms, such as specific acyltransferases, to incorporate these fatty acids efficiently into seed lipids.
authors.affiliation: Centre for Novel Agricultural Products, Department of Biology, University of York, PO Box 373, York YO10 5YW, UK.
authors.forename: Tony R
authors.initials: TR
authors.lastname: Larson
authors.forename: Teresa
authors.initials: T
authors.lastname: Edgell
authors.forename: James
authors.initials: J
authors.lastname: Byrne
authors.forename: Katayoon
authors.initials: K
authors.lastname: Dehesh
authors.forename: Ian A
authors.initials: IA
authors.lastname: Graham
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D029688:Brassica napus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D031562:Cuphea / Q000235:genetics / Q000378:metabolism; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism*; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D030821:Plants, Genetically Modified / Q000378:metabolism*; D012639:Seeds / Q000378:metabolism*
chemical_list: D000214:Acyl Coenzyme A; D005227:Fatty Acids; D008055:Lipids