Engineering lignin composition in plant cell walls for deconstructable biofuels feedstocks or resilient biomaterials

Genetic manipulation of the biopolymers that compose plant cell walls is emerging as a powerful tool to produce designer biomass with properties that may be specifically tailored to various applications. I will present our investigation of several genetic variants of Arabidopsis: the wild type, which makes a lignin polymer of primarily guaiacyl (G) and syringyl (S) monomeric units, the fah1 mutant, which makes lignin from almost exclusively G subunits, and a ferulate 5-hydroxylase (F5H) overexpressing line (C4H:F5H) that makes lignin from S subunits. Using multiscale, multimodal imaging techniques, we show that biomass of the transgenic with predominantly S-lignin is more susceptible to deconstruction by thermochemical treatment than the other variants, and that the transgenic with predominantly G-lignin is the most recalcitrant to thermochemical deconstruction.  These structural changes in the cell wall facilitate enhanced enzymatic saccharification of the high-S transgenic tissue with respect to the wild type, while the high-G variant is clearly the least digestible of the pretreated materials. Finally, we show by contact resonance force microscopy, an atomic force microscopy technique, that cell walls of the high-S transgenic are significantly less stiff in the region of the compound middle lamella relative to wild type and high-G variant. These results imply the utility of genetic modification of lignin for enhanced biofuels production as well as specialized biomaterials applications.