title: Heterologous expression of flax PHOSPHOLIPID:DIACYLGLYCEROL CHOLINEPHOSPHOTRANSFERASE (PDCT) increases polyunsaturated fatty acid content in yeast and Arabidopsis seeds.
abstract: BACKGROUND
  Flax (Linum usitatissimum L.) is an agriculturally important crop with seed oil enriched in α-linolenic acid (18:3 (cisΔ9, 12, 15); ALA). This polyunsaturated fatty acid (PUFA) is the major determinant for the quality of flax seed oil in food, nutraceuticals and industrial applications. The recently identified enzyme: phosphatidylcholine diacylglycerol cholinephosphotransferase (PDCT), catalyzes the interconversion between phosphatidylcholine (PC) and diacylglycerol (DAG), and has been shown to play an important role in PUFA accumulation in Arabidopsis thaliana seeds.
  
  
  METHODS
  Two flax PDCT genes were identified using homology-based approach.
  
  
  RESULTS
  In this study, we describe the isolation and characterization of two PDCT genes from flax (LuPDCT1 and LuPDCT2) with very high nucleotide sequence identity (97%) whose deduced amino acid sequences exhibited approximately 55% identity with that of A. thaliana PDCT (AtROD1). The genes encoded functionally active enzymes that were strongly expressed in developing embryos. Complementation studies with the A. thaliana rod1 mutant demonstrated that the flax PDCTs were capable of restoring PUFA levels in planta. Furthermore, PUFA levels increased in Saccharomyces cerevisiae when the flax PDCTs were co-expressed with FATTY ACID DESATURASES (FADs), FAD2 and FAD3, while seed-specific expression of LuPDCT1 and LuPDCT2 in A. thaliana resulted in 16.4% and 19.7% increases in C18-PUFAs, respectively, with a concomitant decrease in the proportion of oleic acid (18:1 (cisΔ9); OA).
  
  
  CONCLUSIONS
  The two novel PDCT homologs from flax are capable of increasing C18-PUFA levels substantially in metabolically engineered yeast and transgenic A. thaliana seeds. These flax PDCT proteins appear to play an important dual role in the determination of PUFA content by efficiently channelling monounsaturated FAs into PC for desaturation and moving the resulting PUFAs out of PC for subsequent use in TAG synthesis. These results indicate that flax PDCTs would be useful for bioengineering of oil crops to increase PUFA levels for applications in human food and nutritional supplements, animal feed and industrial bioproducts.
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, Canada. naaruna@ualberta.ca.
authors.forename: Aruna D
authors.initials: AD
authors.lastname: Wickramarathna
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, Canada. siloto@ualberta.ca.
authors.forename: Rodrigo M P
authors.initials: RM
authors.lastname: Siloto
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, Canada. mietkiew@ualberta.ca.
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Mietkiewska
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, Canada. ssinger@ualberta.ca.
authors.forename: Stacy D
authors.initials: SD
authors.lastname: Singer
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, Canada. xp2@ualberta.ca.
authors.forename: Xue
authors.initials: X
authors.lastname: Pan
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, T6G 2P5, Canada. weselake@ualbert.ca.
authors.forename: Randall J
authors.initials: RJ
authors.lastname: Weselake
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D044943:Fatty Acid Desaturases / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D019597:Flax / Q000235:genetics / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D030821:Plants, Genetically Modified; D012441:Saccharomyces cerevisiae; D012639:Seeds / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D013997:Time Factors; D017855:Transferases (Other Substituted Phosphate Groups) / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D005231:Fatty Acids, Unsaturated; D044943:Fatty Acid Desaturases; C545204:ROD1 protein, Arabidopsis; D017855:Transferases (Other Substituted Phosphate Groups)