1-05: Enhanced bioprocessing of maize cell wall mutants

Modification of lignin subunit composition can significantly increase the yield of fermentable sugars from maize stover.  The brown midrib1 (bm1) and bm3 mutations each increase the yield of glucose per gram dry stover by 50% relative to the wild-type control (inbred A619).  When combined in a near-isogenic bm1-bm3 double mutant, the two mutations act in an additive manner, resulting in a doubling of the yield of glucose.  Even though there is no apparent increase in cellulose content, based on kinetic studies both the rate of hydrolysis and the overall yield of glucose increase as a result of the mutations.  We are investigating the basis of the enhanced hydrolysis in these bm mutants by assaying the adsorbance of cellulases to stover, using recombinant proteins consisting of the cellulose binding module (CBM) isolated from Trichoderma reesei endoglucanases labeled with green-fluorescent protein (GFP). Because of lignin autofluorescence, this approach can not be performed in situ, but instead has to rely on a fluorescence subtraction assay. We have also shown that biomass from these mutants yields high levels of fermentable sugars under less severe pretreatment conditions compared to biomass from wild-type control plants. The more efficient cell wall deconstruction in these mutant can thus be viewed as genetic pretreatment.  The combined data from these experiments will be of value for the design of plant cell wall composition in such a way that agronomic properties and biomass conversion are optimally balanced.