15-03: Expression of cell wall degrading enzymes in transgenic maize improves biomass hydrolysis

Expression of cell wall degrading enzymes in biomass relevant crops is a proposed means to lower the costs of pretreatment and enzymatic hydrolysis to produce fermentable sugars.  At Agrivida, we expressed several cell wall degrading enzymes in maize.  Enzymes destined for plant expression were chosen based on their thermal and pH tolerances as well as their performance in an in vitro biomass hydrolysis assay.  Using these criteria, we chose xylanase and cellulase enzymes that generated up to 95% glucose yield from pretreated corn stover in 32 hours.  The selected xylanases and cellulases were expressed in maize and accumulated in green tissue and grain up to 16% total soluble protein in selected transgenic events.  Furthermore, these enzymes were present and active in stover, demonstrating their stability throughout senescence.    In contrast to cellulases, xylanase accumulation in maize resulted in several detrimental phenotypes.  These phenotypes could be rescued by the expression of intein-modified xylanases which were inactive during plant development then induced post-harvest.    The stover resulting from these plants was pretreated and enzymatically hydrolyzed using in-house methods tailored to complement the activity of the heterologous enzymes.  The presence of cellulase and xylanase enzymes within transgenic stover aided biomass hydrolysis resulting in up to a 96% increase in glucose yield as compared to wild-type stover.   Agrivida is developing technology that enables the accumulation of wild-type and intein-modified enzymes in maize that improve the production of fermentable sugars from renewable biomass.