Anybody who has spent a night huddled about a warming campfire knows how much energy is stored in wood. With the simple application of heat, you can start a chain reaction that releases this energy in a self-sustaining manner (known as “fire.”) Just a single log of wood has enough energy to heat a group of weary campers for hours — but it’s this very slow release that makes direct burning inefficient for use in most contexts. Combustion engines require an explosive force that raw wood just can’t provide, which is frustrating because we know that there’s ample energy in there. Any extract that can make some natural energy available in a more useful form is called a biofuel, and science has spent a long time trying to invent one that can extract the energy in wood cheaply enough to replace fossil fuels in personal and industrial contexts.

Probably the most confounding impediment to extracting wood’s energy, usually as an alcohol, is a protein called lignin. Lignin is the main source of wood’s rigidity, a vitally important protein for any plant that wishes to grow tall and thin without falling over. In the evolutionary competition to reach new heights and unfettered access to the sun, trees have come to absolutely pack their cells with this enormous protein. Arrays of ligninocellulose support everything from leaf stems to the trunks of the giant forest conifers and make biofuel production dramatically more expensive than it might otherwise be.

New research published in Science, however, has grown a number of plants with far less lignin than normal, an innovation that could drastically decrease the cost of biofuel production from wood. The breakthrough comes soon after the discovery that lignin synthesis is actually dependent on two enzymes, as opposed to just the one previously known. Simply knocking out the historical lignin gene left the plants totally incapable of growth — hardly a fix. However, with the discovery that an enzyme called caffeoyl shikimate esterase (CSE) is also heavily involved, the researchers seem to have stumbled on a way to decrease lignin concentrations while leaving the plant free to grow.

In their experiments, CSE knockout mutants contained 36% less lignin than their regular counterparts and they ended up only a third smaller. They remained upright, rather than snapping or bending as we might have feared. They’re not the most robust plants in the world — if high levels of lignin didn’t offer a competitive advantage, evolution would have reduced its production a long time ago. Still, under the nurturing hand of biofuel farmers these mutants would have no need to compete with wild-type plants, and could fare quite well.

The irony of the lignin problem for biofuel production is that lignin is actually one of the highest-energy molecules in wood, overall. When burning wood, lignin releases far more energy per molecule than cellulose or any of the more famous arboreal constituents, but its extreme toughness makes it a confounding variable for chemical extraction. Fuel isn’t the only product that abhors lignin, either, as the production of goods like paper also require lignin extraction. That makes this breakthrough widely applicable.

In terms of large-scale application, wood will probably remain a secondary biofuel simply due to the slow growth rate of trees. Even given hopes that we could overcome the size reduction of the lignin mutants, more rapid-growth species like corn and soybean would probably be more practical overall. However, there is a generalizable proof of concept here in reverse-engineering our potential fuel species to tailor them for later industrial processes. In addition, much of the current wood biofuel production comes from waste wood, rather than from trees grown specifically for fuel production. If certain conventional applications for wood can work with lignin-reduced species, this research could make their wastes vastly more useful.

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Research paper: doi: 10.1126/science.1241602 — “Caffeoyl Shikimate Esterase (CSE) Is an Enzyme in the Lignin Biosynthetic Pathway”