Transgenic Expression of Accessory Hemicellulases in Arabidopsis and Impact on Fibre Chemistry, Fibre Processing, and Plant Gene Expression

Cellulose, hemicellulose, and lignin are the main structural biopolymers in plant cell walls. Intermolecular linkages between these biopolymers contribute to the recalcitrant nature of lignocellulosic biomass, which reduces the economic feasibility of producing renewable fuels, chemicals, and biomaterials from this resource.;The overall aim of the current Ph.D. thesis was to constitutively express microbial hemicellulases that targets linkages between cell wall components in Arabidopsis thaliana, and evaluate the impact of transgene expression on fibre chemistry, processing, and plant transcript profiles. In total, 24 microbial transgenes encoding 10 enzymatic activities were transferred to arabidopsis. Transgenic arabidopsis expressing a Phanerochaete carnosa family 15 glucuronoyl esterase (PcGCE) was selected for detailed characterisations.;Transgenic plants that constitutively expressed PcGCE consistently displayed a leaf yellowing phenotype. The cell wall in the interfascicular fibre of the transgenic line was thinned by approximately 50%, and the glucose and xylose content of the transgenic lines were reduced by as much as 30% and 35%, respectively. Histological and FT-IR microspectroscopy analyses revealed altered accessibility of xylan binding antibodies and less cross-linked lignin. Xylan recovery from transgenic stems also improved up to 15%.;The transcriptome of arabidopsis transgenic lines expressing PcGCE revealed elevated transcript abundance of genes associated with plant defense response. In contrast, overall, the transcript abundance of secondary cell wall biosynthesis genes were similar between wild-type and transgenic plants.