title: Type 1 diacylglycerol acyltransferases of Brassica napus preferentially incorporate oleic acid into triacylglycerol.
abstract: DGAT1 enzymes (acyl-CoA:diacylglycerol acyltransferase 1, EC 2.3.1.20) catalyse the formation of triacylglycerols (TAGs), the most abundant lipids in vegetable oils. Thorough understanding of the enzymology of oil accumulation is critical to the goal of modifying oilseeds for improved vegetable oil production. Four isoforms of BnDGAT1, the final and rate-limiting step in triacylglycerol synthesis, were characterized from Brassica napus, one of the world's most important oilseed crops. Transcriptional profiling of developing B. napus seeds indicated two genes, BnDGAT1-1 and BnDGAT1-2, with high expression and two, BnDGAT1-3 and BnDGAT1-4, with low expression. The activities of each BnDGAT1 isozyme were characterized following expression in a strain of yeast deficient in TAG synthesis. TAG from B. napus seeds contain only 10% palmitic acid (16:0) at the sn-3 position, so it was surprising that all four BnDGAT1 isozymes exhibited strong (4- to 7-fold) specificity for 16:0 over oleic acid (18:1) as the acyl-CoA substrate. However, the ratio of 18:1-CoA to 16:0-CoA in B. napus seeds during the peak period of TAG synthesis is 3:1. When substrate selectivity assays were conducted with 18:1-CoA and 16:0-CoA in a 3:1 ratio, the four isozymes incorporated 18:1 in amounts 2- to 5-fold higher than 16:0. This strong sensitivity of the BnDGAT1 isozymes to the relative concentrations of acyl-CoA substrates substantially explains the observed fatty acid composition of B. napus seed oil. Understanding these enzymes that are critical for triacylglycerol synthesis will facilitate genetic and biotechnological manipulations to improve this oilseed crop.
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
authors.forename: Jose
authors.initials: J
authors.lastname: Aznar-Moreno
authors.affiliation: Bayer CropScience N.V., Technologiepark 38, B-9052 Ghent, Belgium.
authors.forename: Peter
authors.initials: P
authors.lastname: Denolf
authors.affiliation: Bayer CropScience N.V., Technologiepark 38, B-9052 Ghent, Belgium.
authors.forename: Katrien
authors.initials: K
authors.lastname: Van Audenhove
authors.affiliation: Bayer CropScience N.V., Technologiepark 38, B-9052 Ghent, Belgium.
authors.forename: Stefanie
authors.initials: S
authors.lastname: De Bodt
authors.affiliation: Bayer CropScience N.V., Technologiepark 38, B-9052 Ghent, Belgium.
authors.forename: Steven
authors.initials: S
authors.lastname: Engelen
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
authors.forename: Deirdre
authors.initials: D
authors.lastname: Fahy
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
authors.forename: James G
authors.initials: JG
authors.lastname: Wallis
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA jab@wsu.edu.
authors.forename: John
authors.initials: J
authors.lastname: Browse
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D029688:Brassica napus / Q000235:genetics* / Q000378:metabolism; D051048:Diacylglycerol O-Acyltransferase / Q000235:genetics* / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D010938:Plant Oils / Q000737:chemistry; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D012639:Seeds / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000214:Acyl Coenzyme A; D004075:Diglycerides; D005227:Fatty Acids; D010938:Plant Oils; D051048:Diacylglycerol O-Acyltransferase
keywords: DGAT1; fatty acids; seed lipid metabolism; seed oil; transcript profile.; triacylglycerol