Regulation and functions of polyphenol oxidases (PPOs) in the moss Physcomitrella

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Polyphenol oxidases (PPOs) are almost ubiquitous enzymes, which oxidise polyphenols to highly reactive quinones. The exact biological function of PPOs is poorly understood. Our group identified the first bryophyte PPO gene in the moss Physcomitrella patens with several similarities but also differences to higher plant PPOs. Analysis of the derived amino acid sequence of the Physcomitrella PPO1 gene as well as enzymological studies revealed a strong membrane association. Transcription of PPO1 was shown to vary in the time course of a culture.The project uses the advantages of Physcomitrella as a model plant and focuses on: (a) functional studies on PPO using approaches of overexpression and gene knockout; (b) experiments on regulation of PPO on the levels of transcription and enzyme activity; (c) approaches to investigate enzyme properties such as subcellular localisation and substrate specificity. The chemical structure of the major phenolic compounds from Physcomitrella as potential PPO substrates will be identified. We assume that an elucidation of PPO functions in Physcomitrella as an early land plant can substantially help to understand the physiological and evolutionary role of this almost ubiquitous enzyme.