Cellulose fibers, often obtained from wood, are a key component in products like paper, packaging, tissues, and hygiene products. But within wood, another polymer called lignin is entangled with cellulose. In order to extract the cellulose from wood, the lignin is often broken down with harsh chemicals and separated from the cellulose. The more lignin in the wood, the harder it is to isolate the cellulose fibers.
Rather than just removing lignin from logs, researchers at North Carolina State University sought to lower the proportion of it from the outset. Using the gene-editing tool CRISPR on poplar trees, they modified some of the genes that produce the chemicals that eventually form lignin. Using seven gene-editing strategies, each modifying three to six genes, they were able to slash lignin content up to 35% compared with a nonedited poplar tree when measured after 6 months of growth (Science 2023, DOI: 10.1126/science.add4514).
The researchers started by modeling 69,123 combinations of edits to different genes. Of those, only 347 were predicted to match the team’s required criteria, which included cutting lignin content, altering lignin and wood compositions, and being able to grow to a similar size as unedited trees. Ultimately, the researchers chose the seven editing strategies that they thought would yield the very best wood properties.
Wood edited to have lower lignin content could have several practical benefits, suggest corresponding authors and NC State professors Rodolphe Barrangou and Jack Wang. Lowering the amount of lignin means increasing the amount of cellulose in the wood, so less biomass is needed to yield the same amount of cellulose. Also, on top of requiring harsh chemicals, removing lignin from wood during the pulping process is energy intensive; wood with less lignin would allow savings of both energy and chemicals.
Having the ability to modify lignin in ways that make its removal easier and more efficent that require less of those hazardous chemicals “will bring really transformative benefits to the process of producing sustainable fibers,” says Wang, a tree geneticist.
Steve Strauss, a forest biotechnologist at Oregon State University who was not involved in the study, says this work is “a good start.” He praises the way the researchers used CRISPR to test a number of gene-editing combinations. But he says it will be important to see how the trees grow in the field rather than in the greenhouse and whether these modifications can be translated to tree species that are more important, such as pine or eucalyptus. Strauss also cautions that “if you cut lignin down too much, you get a tree that can’t stand up or can’t conduct water.”
Wang and Barrangou say they didn’t reduce the lignin content beyond what is found in other trees in nature, so they don’t expect major adverse effects from the lower amounts. They also say the next step for the work will be to grow the trees in field trials and that they’ve already started working on tree types of more commercial interest.