CRISPR Gene Editing Helps Breed Poplar Trees for Greener, Cheaper, and More Efficient Fiber Production

Monday - July 17 2023, 14:00 UTC - 1 year ago

NC State researchers have successfully applied CRISPR gene-editing technology to breed poplar trees with reduced levels of lignin, promising greener, cheaper and more efficient fiber production. The remarkable research 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 widespread levels.

Researchers at North Carolina State University (NC State) have successfully applied CRISPR gene-editing technology to breed poplar trees with reduced levels of lignin, a significant barrier to the sustainable production of wood fibers. The research, which offers potential for more efficient, eco-friendly fiber production, was published in the journal Science. The findings hold promise to make fiber production for everything from paper to diapers greener, cheaper, and more efficient.

Led by NC State CRISPR pioneer Rodolphe Barrangou and tree geneticist Jack Wang, a team of researchers used predictive modeling to set goals of lowering lignin levels, increasing the carbohydrate-to-lignin (C/L) ratio, and increasing the ratio of two important lignin building blocks – syringyl to guaiacyl (S/G) – in poplar trees. These combined chemical characteristics represent a fiber production sweet spot, Barrangou and Wang say.

"We’re using CRISPR to build a more sustainable forest," said Barrangou, the Todd R. Klaenhammer Distinguished Professor of Food, Bioprocessing and Nutrition Sciences at NC State and co-corresponding author of the paper. "CRISPR systems provide the flexibility to edit more than just single genes or gene families, allowing for greater improvement to wood properties." .

The team utilized a machine-learning model to predict and sort through almost 70,000 different gene-editing strategies targeting 21 important genes associated with lignin production – some changing multiple genes at a time. The process led to the identification of 347 strategies; more than 99% of those strategies targeted at least three genes.

From there, the researchers selected the seven best strategies that modeling suggested would lead to trees that would attain the chemical sweet spot – 35% less lignin than wild, or unmodified, trees; C/L ratios that were more than 200% higher than wild trees; S/G ratios that were also more than 200% higher than wild trees; and tree growth rates that were similar to wild trees.

From these seven strategies, the researchers used CRISPR gene editing to produce 174 lines of poplar trees. After six months in an NC State greenhouse, an examination of those trees showed reduced lignin content of up to 50% in some varieties, as well as a 228% increase in the C-L ratio in others.

Interestingly, the researchers say, 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 boost pulp yield and reduce so-called black liquor, the primary byproduct of pulping. This could help mills increase the production of sustainable fibers by up to 40%.

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 widespread levels.