GGL-family tissue specific activity
thesisposted on 17.02.2020, 22:12 by Thomas Shafee
Part II Undergraduate Thesis
Department of Biochemistry, University of Cambridge
Supervisor: Paul Dupree
Bench Supervisor: Jenny Mortimer
Xylans are a major component of plant secondary cell walls and their understanding is vital to the optimisation of bio-fuel production. Despite this, the biosynthesis of these polysaccharides is still poorly understood. I have investigated the xylans of root and etiolated hypocotyl tissue and shown significant amounts to be present in both tissues. Previous studies have shown that two genes, GGL4 and GGL5, are responsible for adding glucuronic acid to the xylan backbone of glucuronoxylan in Arabidopsis thaliana stem cell wall (Mortimer, unpublished data). In this study, I investigated the functions of these and related genes, GGL1, GGL3 and GGL6, for addition of glucuronic acid to glucuronoxylan and glucurono-arabinoxylan in root and etiolated hypocotyl secondary cell wall. This was done by structurally characterising the xylan of mutants in these genes by polysaccharide analysis using carbohydrate gel electrophoresis in root and etiolated hypocotyl tissue and high-performance anion exchange chromatography with pulsed amperometric detection. This paper provides evidence that GGL4 and/or GGL5 are responsible for the addition of some glucuronic acid to glucuronoxylan in root and etiolated hypocotyl tissues but are not the sole glucuronic acid transferase in these tissues. In both root and etiolated hypocotyl GGL3 is also required for addition of glucuronic acid. High-performance anion exchange chromatography with pulsed amperometric detection, however, showed no detectable change in the relative monosaccharide composition of the hemicellulosic cell wall. In addition, I report that there is significantly poorer digestion of root xylan than in stem or etiolated hypocotyl which may indicate the presence of glucuronoarabinoxylan in the root.