New way to reduce plant lignin could lead to cheaper biofuels

Scientists from the US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have shown for the first time that an enzyme can be tweaked to reduce lignin in plants.

According to Berkeley Lab, its technique could help lower the cost of converting biomass into carbon-neutral fuels to power cars and other sustainably developed bio-products.

Lignin is a polymer that’s important to a plant’s health and structure. But lignin also permeates plant cell walls and surrounds the sugars trapped inside. This poses a major challenge in efforts to use microbes to ferment the sugar into useful chemicals and fuels.

According to Berkeley Lab, this is because lignin must be chemically broken down in a costly pre-treatment step before the sugar is fermented. The less lignin there is in a plant, the cheaper this pre-treatment step becomes, which is a major goal of the bioenergy industry.

Now, as reported in the journal Plant & Cell Physiology, Berkeley Lab scientists are taking on this challenge in an entirely new way.

 Lignin-production process

They focused on an enzyme called HCT that plays a key role synthesizing lignin in plants. Ordinarily, the enzyme binds with a particular molecule as part of the lignin-production process. The scientists explored whether HCT binds with several other molecules that have similar structures to the original molecule, and they found HCT is pretty indiscriminate with what it accepts.

With this in mind, the researchers introduced another molecule to the enzyme that occupies the binding site usually occupied by the lignin-producing molecule. This swap inhibits the enzyme’s ability to support lignin production.

Initial tests in a model plant show this approach decreases lignin content by 30%  while upping sugar production. What’s more, the technique promises to be much more “tunable” than the current way of reducing plant lignin, in which lignin-producing genes are silenced. This decreases lignin everywhere in a plant and throughout its lifespan, resulting in a weakened plant and a lower sugar yield.

“Our goal is to tune the process so that lignin is reduced in a plant where we want it reduced, such as in tissues that produce thick cell walls, and when we want it reduced, such as later in a plant’s development,” said Dominique Loque, a plant biologist with the Joint BioEnergy Institute (JBEI), a DOE Bioenergy Research Center led by Berkeley Lab, which pursues breakthroughs in the production of cellulosic biofuels.

“This would result in robust bioenergy crops with more sugar and less lignin, and dramatically cheaper pretreatment costs,” Loque said.