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Gene Editing Modifies Tree Genomes to Reduce Lignin

Red stem from gene-editing and original green stem

Poplar plants produced from a gene-editing experiment at University of Georgia, left, had red-colored wood compared to the original green. Red stem is a known side effect of lignin modification. (University of Georgia)

5 June 2015. Plant scientists at University of Georgia used an emerging technique for gene editing to modify the genomes of poplars and related trees to make those varieties better suited for biofuels. The team from the lab of plant biologist Chung-Jui Tsai in Athens published its findings in a recent letter to the journal New Phytologist.

Poplars and related species in the genus Populus, such as aspen and cottonwood, are fast-growing trees used in packing boxes, industrial pallets, and musical instruments. Poplars also grow on marginal land, thus do not compete with food crops. These species, however, have quantities of lignin, a polymer material in trees and other plants that gives strength to the cell walls. That same quality in lignin, however, makes it difficult to break down, thus adding considerable effort and cost when processing poplar wood for commercial products, such as biofuels and pulp for making paper.

Tsai and colleagues sought to edit the genomes of poplars to reduce the concentrations of lignin, as well as tannins, a type of chemical in Populus and other plants that generate proteins poisonous to deer and livestock. The team applied the genome editing technique Crispr, short for clustered, regularly interspaced short palindromic repeats, adapted from a natural process used by bacteria to protect against attack by viruses, where a protein that deactivates or replaces genes binds to targeted RNA molecules generated by the genome. The RNA molecules then guide the editing protein, known as Crispr-associated protein 9 or Cas9, to specific genes needing changes.

Using Crispr, the researchers found they could reduce concentrations of lignin in the plants by 20 percent and condensed tannins by half, compared to trees grown in the wild.  An indicator of reduced lignin levels is a change in the color of the wood from green to red. Red stem, say the authors, is a known side effect of lignin modification in poplars and other Populus varieties, as well as maize, sorghum and pines.

Tsai notes that Crispr is simpler and and more direct than other gene editing techniques. “Compared to some other gene editing techniques,” says Tsai in a university statement, “this is incredibly simple, cost-effective and highly efficient, and it could serve as the foundation for a new era of discovery in plant genetics.” She adds that Crispr “is a mechanism that evolved naturally, but we can borrow the bacteria’s gene-cutting abilities and use it to edit very specific genes in all kinds of organisms, including plants and animals.”

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