ARS | Publication request: Designing Lignins for Improved Biomass Processing

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 11, 2007
Publication Date: March 11, 2008
Citation: Ralph, J., Hatfield, R.D., Grabber, J.H., Lu, F., Kim, H., Marita, J.M. 2008. Designing lignins for improved biomass processing. In: Proceedings of the Funcfiber 2008 International Symposium on the Biology and Biotechnology of Wood, March 10-12, 2008, Umea, Sweden. p. 14

Technical Abstract: Lignin remains one of the most significant barriers to the efficient utilization of cellulosic substrates for biofuels production. If there is a requirement to fractionate the wall first (e.g., by ethanolysis) to provide a clean cellulosic substrate (e.g., for saccharification and fermentation to ethanol), then improving the ease with which lignin can be removed from the complex cell wall becomes paramount. Indications that lignins can be evolved or engineered to be more readily extracted are appearing from current research. For example, the effects on lignification of perturbing most of the genes for enzymes on the monolignol biosynthetic pathway have now been reasonably well studied, particularly in angiosperms. Early studies sought to reduce lignin content with the idea of targeting the key barrier to efficient utilization of plant cell walls in a variety of natural (e.g., ruminant digestibility) and industrial (e.g., chemical pulping, biomass conversion to ethanol) processes. More recently, and particularly for pulping and biomass conversion to ethanol, the idea of altering the composition and structure of the lignin, without necessarily reducing the amount, has also become attractive. The latter approach arose from noting the resilience of the lignification pathway, and its metabolic plasticity. Some transgenics with diminished capacity for biosynthesis of the normal lignin monomers responded by incorporating other available phenolic monomers (often, but not always, pathway intermediates and their derived products) into the polymer. Plant cell wall integrity and plant growth may be impacted, but not always seriously. Obviously, incorporating new phenolics into lignin produces a polymer with a different structure and, therefore, different chemical and physical properties. Not surprisingly, some of these modifications allow for improved biomass conversion efficiencies. Given that monomer substitution in the lignification process is now well authenticated in various transgenic plants, it is opportune to begin explorations into designing lignins to be readily processed