Diversion of Lignin Precursor Reduces Content and Improves Biomass Saccharification Efficiency
Lignin confers recalcitrance to plant biomass used for producing biofuels and bioproducts. The metabolic steps for the synthesis of lignin building blocks belong to the shikimate and phenylpropanoid pathways. Genetic engineering efforts to reduce lignin content typically have employed gene knockout or gene silencing techniques to constitutively repress one of these metabolic pathways. Recently, researchers at the Department of Energy’s Joint BioEnergy Institute (JBEI) employed a new strategy using gain of function. In this method, expression of a 3-dehydroshikimate dehydratase (QsuB from Corynebacterium glutamicum) was targeted to the plastids of Arabidopsis to convert 3-dehydroshikimate—an intermediate of the shikimate pathway—into protocatechuate. This enzymatic conversion diverted lignin precursor into protocatechuate and related molecules and away from lignin precursors. Compared to wild-type plants, Arabidopsis lines expressing QsuB contained reduced levels of lignin deposition in the cell walls. Because this strategy is a gain of function, its expression can be controlled by selective promoters, thus offering better spatiotemporal control of lignin deposition than the gene knockout or gene silencing strategies. Finally, biomass from these engineered Arabidopsis lines exhibits more than a twofold improvement in saccharification efficiency. This result confirms that QsuB expression in plants, in combination with specific promoters, is a promising gain-of-function strategy for spatiotemporal reduction of lignin in plant biomass.
Eudes, A., N. Sathitsuksanoh, E. E. Baidoo, A. George, Y. Liang, F. Yang, S. Singh, J. D. Keasling, B. A. Simmons, and D. Loqué. 2015. “Expression of a Bacterial 3-Dehydroshikimate Dehydratase Reduces Lignin Content and Improves Biomass Saccharification Efficiency,” Plant Biotechnology Journal, DOI: 10.1111/pbi.12310.