title: The syringaldazine-oxidizing peroxidase PXP 3-4 from poplar xylem: cDNA isolation, characterization and expression.
abstract: The cell wall polymer lignin is believed to be condensed by specific cell wall-localized oxidoreductases. In many plants species, including poplar, the peroxidase-directed oxidation of the lignin analogue syringaldazine (SYR) has been localized to cells that undergo secondary wall formation, a process that includes lignification. As a first step to analyse the corresponding peroxidases. we have isolated previously two anionic isoenzymes (PXP 3-4 and PXP 5) from poplar xylem (Populus trichocarpa), which use SYR as a substrate. Here, we demonstrate that these enzymes are responsible for the visualized SYR oxidation in the developing xylem. The cDNA that corresponds to PXP 3-4 was isolated and the deduced protein was found closely related to the other SYR-oxidizing peroxidase PXP 5 (ca. 98% of identity). PXP 3-4 was expressed in a baculovirus expression system yielding high levels of active peroxidase (3 mg/l medium). The heterologously produced protein showed characteristics similar to those of the corresponding protein from poplar xylem (enzymatic properties, isoelectric point, and migration in a native gel). PXP 3-4 was expressed in the stem and in the root xylem. The data demonstrate that PXP 3-4 (and/or PXP 5) are present in differentiating xylem. supporting a function in secondary cell wall formation.
authors.affiliation: Vakgroep Moleculaire Genetica, Departement Plantengenetica, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Universiteit Gent, Belgium.
authors.forename: J H
authors.initials: JH
authors.lastname: Christensen
authors.forename: S
authors.initials: S
authors.lastname: Overney
authors.forename: A
authors.initials: A
authors.lastname: Rohde
authors.forename: W A
authors.initials: WA
authors.lastname: Diaz
authors.forename: G
authors.initials: G
authors.lastname: Bauw
authors.forename: P
authors.initials: P
authors.lastname: Simon
authors.forename: M
authors.initials: M
authors.lastname: Van Montagu
authors.forename: W
authors.initials: W
authors.lastname: Boerjan
mesh_terms: D000595:Amino Acid Sequence; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D006835:Hydrazones / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014197:Trees / Q000201:enzymology / Q000235:genetics*
chemical_list: D018076:DNA, Complementary; D006835:Hydrazones; D007527:Isoenzymes; D010940:Plant Proteins; D012333:RNA, Messenger; C009370:syringaldazine; C442336:PXP 3-4 protein, Populus trichocarpa; D010544:Peroxidases