Researchers at North Carolina State University (NCSU) have used a CRISPR gene-editing system to breed poplar trees with reduced levels of lignin, the major barrier to the sustainable production of wood fibres, while improving their wood properties.

The findings – published in the journal, Science – hold promise to make fibre production for everything from paper to diapers greener, cheaper and more efficient.

Clustered regularly interspaced short palindromic repeats (CRISPR) are the hallmark of a bacterial defence system that forms the basis of genome editing technology.

Led by Rodolphe Barrangou and tree geneticist Jack Wang, a team of researchers used predictive modelling 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 fibre production sweet spot, Barrangou and Wang say.

Machine learning

The machine-learning model predicted and then sorted through almost 70,000 different gene-editing strategies targeting 21 important genes associated with lignin production – some changing multiple genes at a time – to arrive at 347 strategies. More than 99% of those strategies targeted at least three genes.

From there, the researchers selected the seven best strategies that modelling 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 NCSU 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.

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 by-product of pulping, which could help mills produce up to 40% more sustainable fibres.

The 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 green-house environment.

TreeCo

Building on the long-standing legacy of innovations in the fields of plant sciences and forestry at NCSU, Barrangou and Wang created a start-up called TreeCo in 2019 to advance the use of CRISPR technologies in forest trees.

From the machine learning experience, TreeCo designs the method of delivery. Knowing exactly what will work most efficiently is probably the most challenging aspect of the journey, but TreeCo has demonstrated efficiencies in some species as high as 94%.

TreeCo works with elite germplasm to ensure the very best trees are enhanced genetically at a speed and scale impossible using conventional techniques. Starting with elite commercial germplasm enables genetic improvement of the most desirable genotypes.

Once edits occur in some cells, the team ensures the regeneration of healthy edited clones that are nurtured towards a path to the green-house. Their proprietary know-how in tissue culture applies to a range of commercial species of interest.

Edited trees are grown in the green-house to test the impact of the altered genotypes on the corresponding phenotypes and validate machine-learning informed predictions. For more information, visit https://tree-co.com/technology/

Comments