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Zhang, Zhonghang

University of British Columbia

The plant cuticle plays important roles in organ development and adaptation to stresses. Cuticular waxes are mixtures of very-long-chain fatty acid derivatives, also comprising cyclic compounds. The biosynthesis of the common wax constituents and specialty compounds occurring in some plant species has been researched. However, little is known about how mid-chain hydroxyls may also be introduced during hydrocarbon chain formation by Claisen condensations. In my Ph.D studies, I first focused on the wax composition and biosynthesis of specialty wax compounds of Drimys winteri. In Chapter 3, I first investigate the morphology and composition of the Drimys winteri leaf surface. The stomatal plugs on the abaxial leaf surface consist of cutin polymer with sub-micron cavities and tubule-shaped wax crystals above the cutin. I also found the major Drimys winteri wax compound, nonacosan-10-ol, likely has its functional group established by Claisen condensation before the hydrocarbon chain is fully formed, and not by hydroxylation afterwards. The wax mixture also comprised various alkanediols, alkanetriols and ketols with characteristic constellations of hydroxyl groups, suggesting P450 enzymes act alone and in tandem to hydroxylate both secondary alcohols and their diol derivatives. In Chapter 4, methyl ketones, 2-alkanols and δ-lactones were identified as minor constituents of the wax mixture on the Drimys winteri leaves, and their chain length distributions imply characteristic chain length patterns of intermediates derived from the fatty acid elongation complexes involved. In Chapter 5, I focus on the crucial condensing enzymes which catalyze Claisen condensations growing the hydrocarbon chains into very-long-chain fatty acyls. For this, I used the model plant Arabidopsis to investigate the roles of condensing enzymes β-ketoacyl-CoA synthases (KCSs). Mutants lacking one of these enzymes, KCS3, displayed sepal fusions, chain length shifts in the cuticular waxes of several organs, and altered guard cell surface structures. A similar enzyme KCS12, had redundant effects on sepal fusion and bud wax composition with KCS3. In contrast, mutation of the KCS19 led to seed fusions and altered chain length in suberin of seed coats. Overall, all three KCSs were thus found involved in forming very-long-chain compounds coating various Arabidopsis organ surfaces.

Text

2024-04-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87861

Botany

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/