title: The polyphenol oxidase gene family in poplar: phylogeny, differential expression and identification of a novel, vacuolar isoform.
abstract: Polyphenol oxidases (PPOs) are oxidative enzymes that convert monophenols and o-diphenols to o-quinones using molecular oxygen. The quinone products are highly reactive following tissue damage and can interact with cellular constituents and cause oxidative browning and cross-linking. The induction of PPO in some plants as a result of wounding, herbivore attack, or pathogen infection has implicated them in defense. However, PPO-like enzymes that act as specific hydroxylases, for example in lignan and pigment biosynthesis, have also been discovered. Here, we present the first genome-enabled analysis of a PPO gene family. The Populus trichocarpa genome was found to contain a minimum of nine complete PPO genes, and seven of these were characterized further. The PPO gene family includes both recently duplicated and divergent sequences that are 36-98% identical at the amino acid level. Gene expression profiling in poplar tissues and organs revealed that the PPO genes are all differentially expressed during normal development, but that only a small subset of PPO genes are significantly upregulated by wounding, methyl jasmonate or pathogen infection. Our studies also identified PtrPPO13, a novel PPO gene that is predicted to encode an N-terminal signal peptide. Transient expression of green fluorescent protein fusions demonstrated its localization to the vacuolar lumen. Together, our findings show that the poplar PPO family is diverse and is likely linked to diverse physiological functions.
authors.affiliation: Centre for Forest Biology, Department of Biology, University of Victoria, Stn CSC, PO Box 3020, Victoria, BC V8W 3N5, Canada.
authors.forename: Lan T
authors.initials: LT
authors.lastname: Tran
authors.forename: C Peter
authors.initials: CP
authors.lastname: Constabel
mesh_terms: D000085:Acetates / Q000494:pharmacology; D000595:Amino Acid Sequence; D001483:Base Sequence; D004156:Catechol Oxidase / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D003517:Cyclopentanes / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D018745:Genome, Plant / Q000235:genetics; D023281:Genomics; D049452:Green Fluorescent Proteins; D008969:Molecular Sequence Data; D054883:Oxylipins / Q000494:pharmacology; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000494:pharmacology; D030821:Plants, Genetically Modified; D059808:Polyphenols / Q000378:metabolism; D032107:Populus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics* / Q000378:metabolism; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014617:Vacuoles / Q000378:metabolism*
chemical_list: D000085:Acetates; D003517:Cyclopentanes; D054883:Oxylipins; D010937:Plant Growth Regulators; D059808:Polyphenols; D020033:Protein Isoforms; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; C072239:methyl jasmonate; D004156:Catechol Oxidase