CRISPR-modified poplar trees (left) and wild poplar trees grow in an NC State greenhouse. Credit: Chenmin Yang, NC State University
Key points:
- Researchers used machine learning models and CRISPR to target fiber’s chemical sweet spot.
- The gene editing resulted in more sustainable production of wood fibers, which are involved in the manufacturing of everything from paper to diapers.
- The new fiber production could reduce greenhouse gases by up to 20%.
Researchers at North Carolina State University used a CRISPR gene-editing system to breed poplar trees with reduced levels of lignin—the major barrier to sustainable production of wood fibers—while improving their wood properties.
The scientists used predictive modeling to figure out which genes could combine to hit fiber’s sweet spot—which they deduced to be 35% less lignin than wild trees; carbohydrate to lignin (C/L) ratios 200% higher than wild trees; syringyl to guaiacyl (S/G) ratios 200% higher than wild trees; and tree growth rates similar to wild trees.
The model predicted and sorted through almost 70,000 different gene editing strategies targeting 21 genes associated with lignin production to arrive at 347 strategies. More than 99% of those strategies targeted at least three genes. The team then chose 7 of those strategies, using CRISPR to produce 174 lines of poplar trees.
According to the study results, published in Science, after six months in an NC State greenhouse, the trees showed reduced lignin content of up to 50% in some varieties, as well as a 228% increase in the C/L ratio. Interestingly, more significant lignin reductions were shown in trees with four to six gene edits, although trees with three gene edits showed lignin reduction of up to 32%. Single-gene edits failed to reduce lignin content much at all, showing that using CRISPR to make multigene changes could confer advantages in fiber production.
The study also included sophisticated pulp production mill models that suggest reduced lignin content in trees could increase pulp yield and reduce so-called black liquor, the major byproduct of pulping, which could help mills produce up to 40% more sustainable fibers.
Finally, the efficiencies found in fiber production could reduce greenhouse gases associated with pulp production by up to 20% if reduced lignin and increased C/L and S/G ratios are achieved in trees at industrial scale.
Next steps include continued greenhouse tests to see how the gene-edited trees perform compared to wild trees. Later, the team hopes to use field trials to gauge whether the gene-edited trees can handle the stresses provided by life outdoors, outside the controlled greenhouse environment.