Dissertation
Towards understanding the physiological roles of plant laccases
Washington State University
Doctor of Philosophy (PhD), Washington State University
05/2010
DOI:
https://doi.org/10.7273/000006129
Abstract
Plant laccases have been implicated to play a role in a wide range of physiological functions in several plants, however, with no definite biochemical or genetic evidence. This dissertation in part describes various genetic and biochemical approaches towards understanding the in planta roles of a laccase multigene family in Arabidopsis thaliana. Using a genomics approach, we cloned and determined expression patterns of the 17-membered laccase gene family. The unique cell-type expression patterns observed in this study can now help provide new leads and/or strategies into determining their precise physiological/biochemical roles. However, analysis, through reverse genetics of single laccase knockouts in Arabidopsis gave no visible phenotype for the mutants examined except for the homozygous mutant lac15. The latter has a pale yellow seed coat when compared to the brown seed coat in the wild-type, suggesting a physiological/biochemical role in condensed tannin oxidation. Furthermore, heterologous expression and subsequent analysis of one of the Arabidopsis laccase, LAC12, suggested its broad substrate versatility as observed through activity towards wide range of substrates such as monolignols, epicatechin and pentagalloylglucose. In Tellima grandiflora, a putative laccase-like oxidase was reportedly involved in oxidative C-C intramolecular coupling leading to formation of tellimagrandin II. In our studies, however, no evidence to support this biochemical process was observed. By contrast, in this study, an enzyme involved in C-C coupling that led to formation of tellimagrandin II was detected and localized to isolated chloroplasts. Therefore, another class of oxidases is most likely to exist in these organelles. Polyphenol oxidases are proposed as the enzymatic candidates because of their localization to plastids and also their ability to catalyze oxidative coupling reactions. These findings herein thus place the coupling enzyme in the same subcellular compartments as for the substrate and related pathway products. The results from the present study thus partially address the previous enigma of enzymatic oxidative transformations leading to this broad class of hydrolyzable ellagitannins.
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Details
- Title
- Towards understanding the physiological roles of plant laccases
- Creators
- Phanikanth Venkata Turlapati
- Contributors
- Norman G. Lewis (Chair)John A Browse (Committee Member) - Washington State University, Institute of Biological ChemistryBernd M. Lange (Committee Member) - Washington State University, Institute of Biological ChemistryWilliam B Davis (Committee Member) - Washington State University, School of Molecular Biosciences
- Awarding Institution
- Washington State University
- Academic Unit
- Program in Molecular Plant Sciences
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 350
- Identifiers
- 99901055119201842
- Language
- English
- Resource Type
- Dissertation