title: Cloning and characterization of an acyl-CoA-dependent diacylglycerol acyltransferase 1 (DGAT1) gene from Tropaeolum majus, and a study of the functional motifs of the DGAT protein using site-directed mutagenesis to modify enzyme activity and oil content.
abstract: A full-length cDNA encoding a putative diacylglycerol acyltransferase 1 (DGAT1, EC 2.3.1.20) was obtained from Tropaeolum majus (garden nasturtium). The 1557-bp open reading frame of this cDNA, designated TmDGAT1, encodes a protein of 518 amino acids showing high homology to other plant DGAT1s. The TmDGAT1 gene was expressed exclusively in developing seeds. Expression of recombinant TmDGAT1 in the yeast H1246MATalpha quadruple mutant (DGA1, LRO1, ARE1, ARE2) restored the capability of the mutant host to produce triacylglycerols (TAGs). The recombinant TmDGAT1 protein was capable of utilizing a range of (14)C-labelled fatty acyl-CoA donors and diacylglycerol acceptors, and could synthesize (14)C-trierucin. Collectively, these findings confirm that the TmDGAT1 gene encodes an acyl-CoA-dependent DGAT1. In plant transformation studies, seed-specific expression of TmDGAT1 was able to complement the low TAG/unusual fatty acid phenotype of the Arabidopsis AS11 (DGAT1) mutant. Over-expression of TmDGAT1 in wild-type Arabidopsis and high-erucic-acid rapeseed (HEAR) and canola Brassica napus resulted in an increase in oil content (3.5%-10% on a dry weight basis, or a net increase of 11%-30%). Site-directed mutagenesis was conducted on six putative functional regions/motifs of the TmDGAT1 enzyme. Mutagenesis of a serine residue in a putative SnRK1 target site resulted in a 38%-80% increase in DGAT1 activity, and over-expression of the mutated TmDGAT1 in Arabidopsis resulted in a 20%-50% increase in oil content on a per seed basis. Thus, alteration of this putative serine/threonine protein kinase site can be exploited to enhance DGAT1 activity, and expression of mutated DGAT1 can be used to enhance oil content.
authors.affiliation: National Research Council of Canada, Plant Biotechnology Institute, 110 Gymnasium Place, Saskatoon, Canada.
authors.forename: Jingyu
authors.initials: J
authors.lastname: Xu
authors.forename: Tammy
authors.initials: T
authors.lastname: Francis
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Mietkiewska
authors.forename: E Michael
authors.initials: EM
authors.lastname: Giblin
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Barton
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Meng
authors.initials: M
authors.lastname: Zhang
authors.forename: David C
authors.initials: DC
authors.lastname: Taylor
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D051048:Diacylglycerol O-Acyltransferase / Q000235:genetics*; D004883:Erucic Acids; D015723:Gene Library; D017343:Genes, Plant; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010938:Plant Oils / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D014170:Transformation, Genetic; D014280:Triglycerides / Q000096:biosynthesis; D032388:Tropaeolum / Q000201:enzymology* / Q000235:genetics*
chemical_list: D000214:Acyl Coenzyme A; D018076:DNA, Complementary; D018744:DNA, Plant; D004883:Erucic Acids; D010938:Plant Oils; D010940:Plant Proteins; D011994:Recombinant Proteins; D014280:Triglycerides; D051048:Diacylglycerol O-Acyltransferase; C030774:trierucate