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The polyphenol oxidase gene family in poplar: phylogeny, differential expression and identification of a novel, vacuolar isoform

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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.

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Abbreviations

cTP:

Chloroplast transit peptide

GFP:

Green fluorescent protein

MeJA:

Methyl jasmonate

PPO:

Polyphenol oxidase

SP:

Signal peptide

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Acknowledgments

The authors thank Dr. Nicole Dafoe and David McPhie for MeJA-treated tissue samples, Dr. Ian Major for the wounded leaf and catkin tissues, and Dr. Manoela Miranda for the Melampsora medusae-infected tissues. We also thank Dr. Bob Chow and Dr. Erin Star for access and help with the confocal microscope, Dr. Claire Cupples and Shawn Salsiccioli for access and assistance with the biolistics system, and Dr. Eiichiro Ono (Suntory Research Centre, Japan) for providing AmAS1 constructs. We also acknowledge the expert assistance of Brad Binges (Centre for Forest Biology, University of Victoria) for assistance with plant maintenance, and Michael Zifkin for critical reading of the manuscript. This work was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant awarded to CPC.

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  1. Centre for Forest Biology, Department of Biology, University of Victoria, Stn CSC, PO Box 3020, Victoria, BC, V8W 3N5, Canada

    Lan T. Tran & C. Peter Constabel

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  1. Lan T. Tran
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Correspondence to C. Peter Constabel.

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Tran, L.T., Constabel, C.P. The polyphenol oxidase gene family in poplar: phylogeny, differential expression and identification of a novel, vacuolar isoform. Planta 234, 799–813 (2011). https://doi.org/10.1007/s00425-011-1441-9

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