UBC Theses and Dissertations
An investigation into the use of monolignol glucosides in poplar lignin biosynthesis Macdonald, William Kim
The existence of a monolignol glucoside/ β -glucosidase system for the transport and/or storage of lignin precursors in angiosperms is currently speculative. This thesis aimed to identify both active coniferin synthesis in poplar and a coniferin specific β -glucosidase. Radio-tracer feeding studies did not provide evidence of coniferin synthesis in poplar species. However, degenerate polymerase chain reaction was used to isolate partial gene fragments from three family 1 β -glucosidases. The 1823bp cDNA of one of these genes, POP1, was cloned, sequenced and characterized. POP1 is expressed at moderate levels in young leaves but is not expressed to detectable levels in developing xylem. The recombinant POP1 protein cross-reacts with antibodies raised against a pine coniferin β -glucosidase but does not hydrolyze coniferin in in vitro enzyme assays. Based on these findings, it does not appear that POP1 is involved in poplar lignin synthesis. The role of the other family 1 β -glucosidase identified in this study, POP2 and POP3, is unknown. The work presented here only begins to examine the family 1 β -glucosidases in poplar and in no way precludes the existence of coniferin β -glucosidases in this species. If future work manages to find a β-glucosidase that is involved in lignification it would provide valuable evidence towards the existence of a monolignol glucoside/ Pglucosidase transport system and would identify a potential target for lignin modification through genetic engineering.
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