title: Phenylcoumaran benzylic ether reductase prevents accumulation of compounds formed under oxidative conditions in poplar xylem.
abstract: Phenylcoumaran benzylic ether reductase (PCBER) is one of the most abundant proteins in poplar (Populus spp) xylem, but its biological role has remained obscure. In this work, metabolite profiling of transgenic poplar trees downregulated in PCBER revealed both the in vivo substrate and product of PCBER. Based on mass spectrometry and NMR data, the substrate was identified as a hexosylated 8-5-coupling product between sinapyl alcohol and guaiacylglycerol, and the product was identified as its benzyl-reduced form. This activity was confirmed in vitro using a purified recombinant PCBER expressed in Escherichia coli. Assays performed on 20 synthetic substrate analogs revealed the enzyme specificity. In addition, the xylem of PCBER-downregulated trees accumulated over 2000-fold higher levels of cysteine adducts of monolignol dimers. These compounds could be generated in vitro by simple oxidative coupling assays involving monolignols and cysteine. Altogether, our data suggest that the function of PCBER is to reduce phenylpropanoid dimers in planta to form antioxidants that protect the plant against oxidative damage. In addition to describing the catalytic activity of one of the most abundant enzymes in wood, we provide experimental evidence for the antioxidant role of a phenylpropanoid coupling product in planta.
authors.affiliation: Department of Plant Systems Biology, VIB Institute, 9052 Ghent, Belgium Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium.
authors.forename: Claudiu
authors.initials: C
authors.lastname: Niculaes
authors.affiliation: Department of Plant Systems Biology, VIB Institute, 9052 Ghent, Belgium Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium.
authors.forename: Kris
authors.initials: K
authors.lastname: Morreel
authors.affiliation: Department of Biochemistry and the U.S. Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin, Madison, Wisconsin 53726.
authors.forename: Hoon
authors.initials: H
authors.lastname: Kim
authors.affiliation: Department of Biochemistry and the U.S. Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin, Madison, Wisconsin 53726.
authors.forename: Fachuang
authors.initials: F
authors.lastname: Lu
authors.affiliation: Division of Glycoscience, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, 106 91 Stockholm, Sweden.
authors.forename: Lauren S
authors.initials: LS
authors.lastname: McKee
authors.affiliation: Department of Plant Systems Biology, VIB Institute, 9052 Ghent, Belgium Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: Ivens
authors.affiliation: Protein Service Facility, Department for Molecular Biomedical Research, VIB, Ghent University, 9052 Ghent, Belgium.
authors.forename: Jurgen
authors.initials: J
authors.lastname: Haustraete
authors.affiliation: Department of Plant Systems Biology, VIB Institute, 9052 Ghent, Belgium Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium.
authors.forename: Bartel
authors.initials: B
authors.lastname: Vanholme
authors.affiliation: Department of Plant Systems Biology, VIB Institute, 9052 Ghent, Belgium Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium.
authors.forename: Riet De
authors.initials: RD
authors.lastname: Rycke
authors.affiliation: SweTree Technologies, SE-904 03 Umeå, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Hertzberg
authors.affiliation: Zentrum für Holzwirtschaft, Universität Hamburg, D-21031 Hamburg, Germany.
authors.forename: Jorg
authors.initials: J
authors.lastname: Fromm
authors.affiliation: Division of Glycoscience, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, 106 91 Stockholm, Sweden.
authors.forename: Vincent
authors.initials: V
authors.lastname: Bulone
authors.affiliation: Forstbotanik und Baumphysiologie, Büsgen-Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Polle
authors.affiliation: Department of Biochemistry and the U.S. Department of Energy Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin, Madison, Wisconsin 53726.
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.affiliation: Department of Plant Systems Biology, VIB Institute, 9052 Ghent, Belgium Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium woboe@psb.vib-ugent.be.
authors.forename: Wout
authors.initials: W
authors.lastname: Boerjan
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D015536:Down-Regulation; D057075:Enzyme Assays; D015151:Immunoblotting; D017705:Lignans / Q000096:biosynthesis / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D010641:Phenotype; D030821:Plants, Genetically Modified; D032107:Populus / Q000201:enzymology*; D015203:Reproducibility of Results; D013379:Substrate Specificity; D052584:Xylem / Q000201:enzymology*
chemical_list: D000596:Amino Acids; D017705:Lignans; D010088:Oxidoreductases; C118150:phenylcoumaran benzylic ether reductase; D003545:Cysteine