Sugarcane's Sweet Juice of Success
New strains hold potential for less intensive processing
Strains of sugarcane can be genetically engineered to improve biofuel production, all while maintaining or increasing juice production, a new study suggests. By inserting disruptive DNA into sugarcane, researchers altered lignin, a polymer that is found in plant cell walls and is one component of wood. Because lignin intensifies biofuel processing, its modification could make quick-growing sugarcane a more attractive alternative fuel source.
“Researching plant cell walls, and the genetic and environmental factors that influence their development, can significantly impact the way we use plant material for fuels and other products,” says Heather Coleman, assistant professor of biology in the College of Arts and Sciences and the study’s senior author.
In the study, reported Dec. 20, 2016, in Biotechnology for Biofuels, researchers interrupted natural lignin production in sugarcane cell walls and tested the resulting strains for actual lignin production and glucose release. Coleman and colleagues genetically engineered plants to reduce expression of three key lignin production genes. Three of the modified strains had either reduced lignin content, or beneficially altered ratios of lignin building blocks—all of which are predicted to improve biofuel production.
Joining Coleman were lead author Patrick Bewg, Coleman’s previous Ph.D. student at Queensland University of Technology; Charleson Pooviah, Syracuse postdoctoral researcher; John Ralph, professor of biochemistry at University of Wisconsin-Madison; and Wu Lan, previous Ph.D. student at University of Wisconsin-Madison.
Many plant biofuel sources exist, but naturally occurring lignin presents a processing problem in all of them. Bioethanol production in particular relies on cellulase enzymes entering cell walls and breaking down cellulose into sugars, which are fermented into ethanol. Lignin can physically prevent cellulases from getting where they need to go, requiring harsh chemicals or energy-intensive processes to loosen up cell walls, Coleman explains.
By genetically altering cell wall lignin content, producers could sidestep severe pretreatment and make bioethanol production more appealing. Currently, sugarcane biomass is disposed of by burning after its glucose-rich juice is extracted, Coleman says.
“There is a real-world business opportunity to diversify sugar industry products and optimize the raw resource by using the waste product as a source of bioethanol,” she says.
In order to test lignin modification, and confirm consistent juice production, Bewg used high-pressured “biolistics” to introduce tiny, DNA-coated gold beads into undifferentiated sugarcane tissue. The inserted DNA was coupled to an antibiotic resistance gene, used by the researchers to identify plants that incorporated the new genetic material by growing biolistic treated tissue on an antibiotic surface.
The sugarcane plants were grown and processed for juice extraction at the Centre for Tropical Crops and Biocommodities at Queensland University of Technology by Bewg. Based on analysis done at Queensland, University of Wisconsin-Madison and Syracuse, three of the lines had reduced lignin content or a modified balance of lignin subunits, which would improve cellulose activity. What’s more, all of these lines had improved glucose release.
The results go beyond sugar cane processing, Coleman says: “Much of what we do is really about understanding cell wall formation in plants. A couple of the interesting findings that have emerged from this work are that sugarcane lignin has similar characteristics to maize lignin, which is not surprising, but also that different classes of plants may actually have different starting molecules for lignin production.”
She adds that the Coleman lab is always looking for undergraduate or graduate students interested in plant developmental biology or biofuels and can be reached via email.