Designing Low Lignin, High Biomass Yielding Plants

The Science

Down-regulation of the enzyme hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT) in thale cress (Arabidopsis thaliana) and alfalfa (Medicago sativa) leads to strongly reduced lignin levels, reduced recalcitrance of cell walls to sugar release, but severe stunting of the plants. Levels of the stress hormone salicylic acid (SA) are inversely proportional to lignin levels and growth in a series of transgenic alfalfa plants in which lignin biosynthesis has been perturbed at different biosynthetic steps. Reduction of SA levels by genetically blocking its formation or causing its removal restores growth in HCT–down-regulated Arabidopsis, although the plants maintain reduced lignin levels. SA-mediated growth inhibition may occur via interference with gibberellic acid signaling or responsiveness. This data place SA as a central component in growth signaling pathways that either sense flux into the monolignol pathway or respond to secondary cell-wall integrity, and indicate that it is possible to engineer plants with highly reduced cell-wall recalcitrance without negatively impacting growth.


The major barrier to the efficient conversion of biomass from plant feedstocks to biofuels is breaking down the plant cell wall so that the sugars locked within can be released. This barrier is due to the presence of lignin, a complex compound that cross links the walls and provides rigidity to the plant. Plants that are genetically modified to have less lignin can be broken down more easily, but often these plants show severely stunted growth. Plants have a stress hormone (salicylic acid (SA)) that is known to impact plant growth and development and whose levels are inversely proportional to lignin levels. Researchers at the DOE BioEnergy Science Center (BESC) have found that genetically removing SA from Arabidopsis plants that were also modified to produce low levels of lignin restores normal growth to these plants while maintaining low lignin content. These results support the hypothesis that low lignin, high biomass yielding plants can be engineered to produce sustainable biofeedstocks for biofuel production.

Principal Investigator

Richard A. Dixon
Oak Ridge National Laboratory

BER Program Manager

Kari Perez

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Gallego-Giraldo, L., L. Escamilla-Trevino, L. A. Jackson, and R. A. Dixon. 2011. “Salicylic Acid Mediates the Reduced Growth of Lignin Down-Regulated Plants,” Proceedings of the National Academy of Sciences of the United States of America 108(51), 20814–9. DOI:10.1073/pnas.1117873108.