Date of Award
Doctor of Philosophy (PhD)
biofuel, cellulases, transgenic
Abundant cellulose in the secondary cell walls of lignocellulosic biomass provides an alternative source of carbohydrates for ethanol production. However, low efficiency and high cost of conversion of cellulose to glucose prevents the large-scale production of economically viable cellulosic ethanol. Expression of glycosyl hydrolases in plants has been proposed as an ideal replacement for current microbial-cellulase production in order to reduce the investment cost of hydrolases for ethanol production.
In this thesis, a hyperthermophilic endoglucanase, TnCelB, was expressed in hybrid poplar. The transgenic event with highest TnCelB expression level had reduced lignin content, cellulose crystallinity, and resultant more digestible cell wall. Post-harvest heat treatment improved saccharification efficiencies n transgenic poplar events. In the third chapter, a plant expansin-like non-hydrolytic protein, swollenin, was expressed in hybrid poplar. Enhanced saccharification efficiencies were observed from transgenic events. These two case studies confirmed the advantages of producing cell wall degrading enzymes in lignocellulosic biomass for ethanol production from various aspects However, defective plant growth and development was seen in transgenic events in which either enzyme, TnCelB or swollenin was highly expressed. Therefore, inducible hyperexpression systems are required for efficient expression of in planta cell wall degrading enzymes. For this purpose, In Plant ACTivation (INPACT) technology, an inducible, hyperexpression platform, was evaluated in poplar, but failed to drive the extreme expression necessary for application of INPACT in poplar. However, ways forward have been identified to improve this system for implementation in poplar.
With current conventional overexpression technologies, detrimental effects from destructive enzymes on plant hosts are still unconquered challenges for generating ideal biomass. In order to utilize transgenic biomass to produce economically competitive lignocellulosic ethanol, multiple factors including hydrolytic enzymes, overexpression technology, and downstream processes need to be optimized. Endeavors from numerous fields, including molecular biology, chemical engineering, are required to achieve affordable lignocellulosic ethanol.
Xiao, Yao, "Reducing cell wall recalcitrance in poplar through overexpression of cell wall degrading enzymes" (2018). Dissertations - ALL. 944.