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Title: Glucuronoxylan acetylation patterns and site-specific acetyltransferases
Author: Wurman Rodrich, Joel
ISNI:       0000 0004 7968 4475
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Plant biomass is the biggest source of carbon-based materials for several industries such as food, agriculture, textile, construction, and biofuels, among others. Cellulose and xylan are the two major components of plant biomass, and their intermolecular interactions in the cell wall are crucial for plant growth and industrial use. In eudicots, these interactions are determined by the arrangement of the main substitutions on the xylan backbone, O-acetyl (Ac) and glucuronic acid (GlcA) groups. GUX1, GUX2 and GUX3 are largely responsible for transfer of GlcA decorations, each producing a distinct substitution pattern in regions of the xylan molecule known as compatible or incompatible domains, based on the likely ability of the xylan produced to bind to hydrophilic surfaces of cellulose fibrils. However, the elongation of the xylan backbone, the origin of the GlcA patterning, and the xylan acetylation processes are not fully understood. The xylan backbone is synthesised by two partially redundant Xylan Synthase protein Complexes (XSC). Removing subunits of one XSC causes a reduction in xylan length, and affects the GlcA pattern. Xylan acetylation has also been shown to modulate the GlcA pattern, thus, changes in XSC could also affect the acetylation. In the work described in this thesis, mutants with altered XSC composition and no GlcA on xylan were studied. They showed no detectable changes in xylan acetylation patterns. Therefore, the effect on GlcA patterning can be attributed to the shortening of the xylan backbone. Mainly, every other xylose residue is acetylated, but the pattern in other parts of the molecule is unclear. The xylan compatible and incompatible domains were analysed using a combination of xylan-specific hydrolases, carbohydrate gel electrophoresis and tandem mass-spectrometry. The structures found in the compatible domain were consistent with the reported acetylation pattern, but the incompatible domain exhibited consecutive acetylated xylosyl residues. Arabidopsis mutants for candidate xylan O-acetyltransferases were analysed, and four genes were found to be involved in xylan acetylation. TBL32 and TBL33 were shown to be responsible for the acetylation of xylosyl residues that carry a GlcA. Mutants in TBL3 and TBL28 also affected xylan acetylation, opening opportunities for discovering new xylan acetylation functions.
Supervisor: Dupree, Paul Sponsor: Cambridge Trust ; Conicyt Becas Chile
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Xylan ; cell wall ; glucuronic acid ; acetylation