Engineered Sorghum Bagasse Enables a Sustainable Biorefinery with p-Hydroxybenzoic Acid-Based Deep Eutectic Solvent.

Integrating multidisciplinary research in plant genetic engineering and renewable deep eutectic solvent can facilitate a sustainable and economic biorefinery. Herein, we leveraged a plant genetic engineering approach to specifically incorporate C 6 C 1 monomers into the lignin structure. By expressing the bacterial ubiC gene in sorghum, p -hydroxybenzoic acid (PB)-rich lignin was incorporated into the plant cell wall, while this monomer was completely absent in the lignin of the wild-type (WT) biomass. A deep eutectic solvent (DES) was synthesized with choline chloride (ChCl) and PB and applied to the pretreatment of the PB-rich mutant biomass for a sustainable biorefinery. The release of fermentable sugars was significantly enhanced (~190% increase) compared to untreated biomass by the DES pretreatment. In particular, the glucose released from the pretreated mutant biomass was up to 12% higher than that from the pretreated WT biomass. Lignin was effectively removed from the biomass with the preservation of more than half of the β-Ο-4 linkages without condensed aromatic structures. Hydrogenolysis of the fractionated lignin was conducted to demonstrate the potential of phenolic compound production. In addition, a simple hydrothermal treatment could selectively extract PB from the same engineered lignin, showing a possible circular biorefinery. These results suggest that the combination of PB-based DES with engineered PB-rich biomass is a promising strategy to achieve a sustainable closed-loop biorefinery.