Molecular and Comparative Phylogenetic Analysis of the Polyphenol Oxidase Gene Family in Poplar (Populus spp.)




Tran, Lan T.

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Polyphenol oxidases (PPOs) are ubiquitous enzymes that oxidize phenols to quinones in the presence of molecular oxygen, often leading to tissue discolouration. They are sometimes considered as defense proteins but other functions, for example in phenolic compound biosynthesis, have also been found. In this thesis, bioinformatic searches were conducted to identify putative PPO genes from available genomes representing five Viridiplantae lineages: chlorophytes, bryophytes, lycophytes, monocotyledonous anthophytes and eudicotyledonous anthophytes. Duplicated PPO genes were found in most land plant genomes. A detailed investigation of the poplar (Populus trichocarpa) PPO gene family found nine genes that exhibit differential expression profiles during development and following stress, of which PtrPPO1 was the only significant wound-inducible PPO gene. A phylogenetic reconstruction of the poplar PPOs identified PtrPPO13 to be an unusual PPO homolog and it was studied in detail. Experimental evidence indicated that PtrPPO13 is expressed in most organs, and unlike most PPOs, is localized to the vacuole. Together, the phylogeny, gene expression and subcellular localization studies suggest that PPOs are likely to have variable physiological functions in plants and that PtrPPO13 is distinct from most typical PPOs.



Bioinformatics, BLAST, chloroplast, confocal microscopy, exons, green fluorescent protein, Physcomitrella, polymerase chain reaction