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UBC Theses and Dissertations

Identifying a native p-hydroxybenzoyl-CoA monolignol transferase gene in poplar MacKay, Heather A.


Woody biomass utilisation for the production of pulp and paper, specialty cellulose and chemicals, and cellulosic biofuels requires significant investment of chemicals and energy. Lignin, a polyphenolic constituent of the secondary cell walls of vascular plants, is a significant impediment for wood processing. As such, delignification is essential for biomass utilisation, and typically relies on the addition of acid or alkali to promote fibre separation, and the recovery of the chemical fractions of the biomass. Increasing the degree of acylation (the process of adding an acyl group, or RCO– group, to a compound) of lignin and/or integrating unique bonds into the lignin polymer backbone can improve the processability of an otherwise chemically stable polymer. In Salix, Populus, and Palmae species, p-hydroxybenzoic acid (pHBA) acylates the monolignols. When these monolignol p-hydroxybenzoate conjugates are incorporated into lignin, pendant ester groups decorate the lignin polymer, and can be easily ‘clipped off’ by mild chemical treatment. Consequently, pHBA is of particular interest in the pursuit of creating designer lignins. p-HYDROXYBENZOYL-COA MONOLIGNOL TRANSFERASE (pHBMT) is the putative enzyme thought to be responsible for decorating monolignols with pHBA. The gene encoding pHBMT, however, remains elusive. In this study a putative pHBMT gene was identified through in vitro enzyme activity assays, and subsequently overexpressed in both A. thaliana and hybrid poplar under the control of the Cauliflower mosaic virus 35S promoter (CaMV35SP) and the Arabidopsis thaliana CINNAMATE-4-HYDROXYLASE promoter (AtC4HP). Although, overexpression of this putative pHBMT did not result in a significant increase in pHBA in the cell walls of A. thaliana, increases were observed in poplar. This result furthers our understandings of the mechanisms driving acylated monolignol biosynthesis, and identified a promising avenue in the pursuit and development of novel transgenic plant varieties with unique lignin properties and commercial applications.

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