01/21/2021
Diversion of Lignin Precursor Reduces Content and Improves Biomass Saccharification Efficiency
Lignin deposited in plant cell walls negatively affects biomass conversion into advanced bioproducts.
The Science
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.
The Impact
Lignin deposited in plant cell walls negatively affects biomass conversion into advanced bioproducts. There is therefore a strong interest in developing bioenergy crops with reduced lignin content or altered lignin structures. Another desired trait for bioenergy crops is the ability to accumulate novel bioproducts, which would enhance the development of economically sustainable biorefineries. As previously demonstrated in the model plant Arabidopsis, expression of a 3-dehydroshikimate dehydratase in plants offers the potential for decreasing lignin content and overproducing a value-added metabolic coproduct (i.e., protocatechuate) suitable for biological upgrading. The choice of promoter to drive QsuB expression should be carefully considered when deploying this strategy to other bioenergy crops. Field-testing of engineered QsuB switchgrass are in progress to assess the performance of the introduced traits and agronomic performances of the transgenic plants.
BER Program Manager
Shing Kwok
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]
References
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 in Switchgrass,” Plant Biotechnology Journal, DOI: 10.1111/pbi.12310.