title: Identification and functional characterization of a flax UDP-glycosyltransferase glucosylating secoisolariciresinol (SECO) into secoisolariciresinol monoglucoside (SMG) and diglucoside (SDG).
abstract: BACKGROUND
  Lignans are a class of diphenolic nonsteroidal phytoestrogens often found glycosylated in planta. Flax seeds are a rich source of secoisolariciresinol diglucoside (SDG) lignans. Glycosylation is a process by which a glycosyl group is covalently attached to an aglycone substrate and is catalyzed by uridine diphosphate glycosyltransferases (UGTs). Until now, very little information was available on UGT genes that may play a role in flax SDG biosynthesis. Here we report on the identification, structural and functional characterization of 5 putative UGTs potentially involved in secoisolariciresinol (SECO) glucosylation in flax.
  
  
  RESULTS
  Five UGT genes belonging to the glycosyltransferases' family 1 (EC 2.4.x.y) were cloned and characterized. They fall under four UGT families corresponding to five sub-families referred to as UGT74S1, UGT74T1, UGT89B3, UGT94H1, UGT712B1 that all display the characteristic plant secondary product glycosyltransferase (PSPG) conserved motif. However, diversity was observed within this 44 amino acid sequence, especially in the two peptide sequences WAPQV and HCGWNS known to play a key role in the recognition and binding of diverse aglycone substrates and in the sugar donor specificity. In developing flax seeds, UGT74S1 and UGT94H1 showed a coordinated gene expression with that of pinoresinol-lariciresinol reductase (PLR) and their gene expression patterns correlated with SDG biosynthesis. Enzyme assays of the five heterologously expressed UGTs identified UGT74S1 as the only one using SECO as substrate, forming SECO monoglucoside (SMG) and then SDG in a sequential manner.
  
  
  CONCLUSIONS
  We have cloned and characterized five flax UGTs and provided evidence that UGT74S1 uses SECO as substrate to form SDG in vitro. This study allowed us to propose a model for the missing step in SDG lignan biosynthesis.
authors.forename: Kaushik
authors.initials: K
authors.lastname: Ghose
authors.forename: Kumarakurubaran
authors.initials: K
authors.lastname: Selvaraj
authors.forename: Jason
authors.initials: J
authors.lastname: McCallum
authors.forename: Chris W
authors.initials: CW
authors.lastname: Kirby
authors.forename: Marva
authors.initials: M
authors.lastname: Sweeney-Nixon
authors.forename: Sylvie J
authors.initials: SJ
authors.lastname: Cloutier
authors.forename: Michael
authors.initials: M
authors.lastname: Deyholos
authors.forename: Raju
authors.initials: R
authors.lastname: Datla
authors.affiliation: Crops and Livestock Research Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, PE C1A 4 N6, Canada. bourlaye.fofana@agr.gc.ca.
authors.forename: Bourlaye
authors.initials: B
authors.lastname: Fofana
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D053898:Biosynthetic Pathways / Q000235:genetics; D002072:Butylene Glycols / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000235:genetics; D057075:Enzyme Assays; D020224:Expressed Sequence Tags; D019597:Flax / Q000201:enzymology* / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005960:Glucosides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006031:Glycosylation; D016695:Glycosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D017705:Lignans / Q000737:chemistry / Q000378:metabolism*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000235:genetics; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D031685:Sesamum / Q000378:metabolism
chemical_list: D002072:Butylene Glycols; D018076:DNA, Complementary; D005960:Glucosides; D017705:Lignans; D010088:Oxidoreductases; C084968:lariciresinol reductase; C084969:pinoresinol reductase; D016695:Glycosyltransferases; C060283:secoisolariciresinol; C090142:secoisolariciresinol diglucoside