December 6, 2023

Traditional tree breeding takes time, but CRISPR gene editing should help speed things up. Now, scientists at North Carolina State University have used CRISPR to tweak the genomes of poplar trees to make them easier to turn into paper products.

Lignin is a natural polymer found in plant branches and stems that holds fibers together, essentially making them harder and stronger. While lignin is important to the health of plants when they are alive, it takes a lot of effort to remove lignin to “degumming” fibers and make paper and other products.

Therefore, scientists have been trying to grow plants with lower lignin content. The problem is, tree genetics is more complicated than you might think, and traditional breeding to select for certain traits can take years to see the results of each experiment. CRISPR gene-editing technology could make this transition even faster.

In the new study, the NC State team attempted to use CRISPR to reduce lignin levels and increase carbohydrate-to-lignin (C/L) and syringyl-to-guaiac (S/G) levels in poplar. The ratio of the two molecules that make up lignin. The right combination of these properties – 35% less lignin than wild trees, and 200% higher C/L and S/G ratios than wild trees – will be the sweet spot for paper production.

To reach this sweet spot, the team used machine learning models to predict and classify nearly 70,000 gene-editing strategies, targeting 21 genes important for lignin production. The researchers narrowed the field to 347 strategies, from which the seven most promising were selected.

Next, the team used CRISPR to genetically engineer 174 poplar trees with the seven recipes and grew them in a greenhouse for six months. Sure enough, many varieties met or even exceeded the sweet spot—some saw a 50% reduction in lignin levels, while others saw a 228% increase in C/L ratios.

The team says the best results came from strategies that involved editing four to six genes, although three genes were enough to reduce lignin by 32%. They found that editing just one gene was simply not enough to have much of an effect.

Downstream, the team modeled how much sustainable pulp production these CRISPR trees could achieve. They found that reducing lignin could help factories produce up to 40 percent more fiber in a more sustainable way and reduce greenhouse gas emissions in the process by up to 20 percent.

In future studies, the team plans to continue growing the edited poplars to see how they fare compared to wild-type trees, and to experiment in outdoor settings.

The study was published in the journal science.

source: North Carolina State University