Engineered Poplar Lignin Improves Wood Degradability
Lignin is an irregular phenolic plant cell wall polymer that is integral to plant strength and function. It is important in bioprocessing of plant biomass because it inhibits deconstruction of plant cell wall sugar polymers, such as cellulose and hemicellulose, into sugar monomers, a key step in biofuel production. The irregular structure and types of linkages among the phenolic monolignol precursors contribute to lignin’s recalcitrance to cleavage and hydrolysis. Interestingly, the enzymes that polymerize lignin are known to be promiscuous and can incorporate nonstandard monolignols if alternate precursors are supplied. Exploiting this promiscuity to construct a lignin more amenable to hydrolysis, Great Lakes Bioenergy Research Center (GLBRC) researchers genetically engineered poplar—an attractive biofuels feedstock—to biosynthesize ferulate conjugated monolignols in the developing cell wall of plant tissues that contain significant amounts of lignin. The ferulate monolignols are of particular interest because they form ester bonds in lignin that are more hydrolysable than the typical ether bonds that normally connect lignin monolignols. The modified lignin altered the amount of sugars released from the poplar cell walls, and the researchers found that mild alkaline pretreatment released as much as double the glucose compared to the unmodified poplar lignin. These studies demonstrate the usefulness of modifying plant lignin as a means to simplify and improve processing of plant biomass and increasing sugar yields from plant biomass for biofuel production. These improvements are important advances in overcoming the technical barriers to an economically viable and sustainable biofuels industry.
Wilkerson, C. G., S. D. Mansfield, F. Lu, S. Withers, J.-Y. Park, S. D. Karlen, E. Gonzales-Vigil, D. Padmakshan, F. Unda, J. Rencoret, and J. Ralph. 2014. “Monolignol Ferulate Transferase Introduces Chemically Labile Linkages into the Lignin Backbone,” Science 344, 90–93. DOI:10.1126/science.1250161.