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Cellulosic Plants Engineered for Improved Biofuel Production

Dominque Loque, right and co-author Henrik Scheller with engineered Arabidopsis plants

Dominque Loque, right and co-author Henrik Scheller with engineered Arabidopsis plants (Roy Kaltschmidt, Berkeley Lab)

Researchers at the Joint BioEnergy Institute in Berkeley, California developed a process to re-engineer the cell walls of plants to make them better feedstocks for biofuels. The team led by bio-engineer Dominique Locque of Lawrence Berkeley National Laboratory, one of the Joint BioEnergy Institute partners and a division of the U.S. Department of Energy, published its findings in the April 2013 issue of the Plant Biotechnology Journal (paid subscription required).

Locque’s team that included members from Shanghai Jiaotong University in China addressed the problem of processing lignocellulosic biomass into a suitable feedstock to make biofuels. Cellulosic plants are rich in complex polysaccharide sugars that can be fermented into ethanol and other biofuels, but those sugars are protected by lignin, a polymer in the cell walls that make the sugars difficult to extract.

A solution for overcoming the lignin barriers to these sugars in a way that still encourages plant growth has so far eluded researchers. “Unfortunately, most efforts to reduce lignin content during plant development,” says Locque, “have resulted in severe biomass yield reduction and a loss of integrity in vessels, a key tissue responsible for water and nutrient distribution from roots to the above-ground organs.” Lignin is not only a problem for biofuels, it also causes difficulties for producers of wood pulp and animal feeds, traditional commercial processors of cellulosic plants.

Locque and colleagues experimented with a synthetic biology process to re-engineer the way plants develop to reduce cell wall barriers and boost polysaccharide sugar content, while still enabling plants to grow. The experiments involved Arabidopsis plants, often used as lab models in much the same way that mice are used in biomedical experiments.

The researchers rewired the regulation of lignin development in Arabidopsis plants by creating an artificial positive feedback loop to disconnect development of secondary cell walls in specific plant tissues. The results showed the plants had less lignin, but more polysaccharide deposits in the cell walls. The team also pretreated the engineered plants to further improve the release of sugars with enzymes, as tests showed comparing treated-engineered plants to wild versions. “In other words,” says Locque, “we accumulated the good stuff, polysaccharides, without spoiling it with lignin.”

Because the cell regulatory process re-engineered by Joint BioEnergy Institute team is well conserved in evolution, the researchers believe the re-engineering technique can be easily applied to other plant species similar in fiber structure to Arabidopsis plants. In addition to greater biofuel production, the technique can also provide benefits to commercial pulping and foraging operations, with stronger cereal straws, and reduced crop lodging and seed losses.

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