Wood is one of the major carbon reservoirs on Earth. Wood cell walls consist of a compound middle lamella and secondary wall layers that are composed of a cellulose/hemicellulose network impregnated with lignin. In the wood of Populus spp., these polymers occur in approximate proportions of 45% cellulose, 25% hemicelluloses, and 20% lignin. Previously, we evolved a set of monolignol 4-O-methyltransferases (M4OMTs) via structure-based iterative saturation mutagenesis. The created enzymes confer significant para-methylation activity to monolignols and their precursors. Expressing a M4OMT variant that exhibits a slight catalytic preference for modifying the syringyl-lignin precursor in poplar resulted in a moderate reduction of total lignin content, but the thioacidolytically cleaved S-lignin monomers from transgenic plants decreased more than 50% compared to those from the wild type plants. NMR analysis further confirmed the relative decrease in S-units and the increase in condensed cross-linkages (e.g., �-5), pointing to a substantial alteration in lignin composition and structure in the transgenic poplar. Concomitantly, the level of cellulosic fibers in the transgenic cell wall was substantially increased about 10 to 15% of the wild type level, whereas hemicellulose content remained relatively unchanged. Preliminary analysis by polarization synchrotron FT-IR revealed that the organization and orientation of cellulose, hemicellulose, and lignin polymers in relation to wood fibre axis were drastically altered in the transgenic wood tissues. As the consequence of cell wall composition and ultra-structural changes, the digestibility of wood biomass was substantially improved; the efficiency of simple sugar release from transgenic wood biomass with cellulase treatment increased about 62%. These data suggest that condensation of lignin does not necessarily correlate with poplar wood biomass digestibility; and M4OMT-mediated alteration of lignin composition in transgenic poplar might globally affect the cell wall's structure and the interactions between cell wall polymers. Such created transgenic plants may provide an advanced bio-material for agro-industrial applications and biofuel production.

Alteration of <i>Populus</i> wood ultra-structure and digestibility via expression of a novel monolignol methyltransferase

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.

Alteration of Populus wood ultra-structure and digestibility via expression of a novel monolignol methyltransferase