Conventional breeding of trees takes time, but CRISPR gene editing should help speed things up. Now, scientists at North Carolina State University have used CRISPR to adjust the genomes of poplar trees to make them easier to turn into paper products.
Lignin is a type of natural polymer found in the branches and stems of plants that holds the fibers together and essentially makes them stiffer and stronger. While it’s important for the health of the plant while alive, lignin needs to be removed, with great effort, to “unglue” the fibers and make paper and other products.
So scientists have been experimenting with growing plants with less lignin. The problem is, tree genetics are more complex than you might expect, and traditional breeding to select for certain traits can take years to see results for each experiment. CRISPR gene editing techniques could make that turn-around much faster.
For the new study, the NC State team experimented with CRISPR to lower lignin levels in poplar trees, and increase the ratios of carbohydrates to lignin (C/L) and syringyl to guaiacyl (S/G), two molecules that make up lignin. These properties in just the right combo – 35% less lignin than wild trees, and C/L and S/G ratios that are each 200% higher than wild trees – would make for a sweet spot in paper production.
To reach this targeted sweet spot, the team used machine-learning models to predict and sort through almost 70,000 gene-editing strategies, targeting 21 genes important for lignin production. This was narrowed down to 347 strategies, from which the researchers selected the seven most promising.
Next, the team used CRISPR to genetically engineer 174 lines of poplar trees following those seven recipes, and grew them in a greenhouse for six months. And sure enough, many varieties met and even exceeded the sweet spot – some reduced lignin levels by as much as 50%, while others saw an increase of 228% in the C/L ratio.
The team said that the best results came from strategies that involved editing four to six genes, although three was enough to hit a decent 32% reduction in lignin. Editing just one gene wasn’t enough to make much of an impact at all, they found.
Downstream, the team modeled how much more sustainable pulp production could be from these CRISPR trees. They found that reducing lignin could help mills produce up to 40% more fibers in a more sustainable way, and reduce greenhouse gas emissions from the process by up to 20%.
In future studies the team plans to continue growing the edited poplars to see how well they survive compared to wild-type trees, and trial them in outdoor environments.
The research was published in the journal Science.
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