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JBEI and USDA researchers boost switchgrass biofuels potential by adding a maize gene; more starch, easier to extract

Researchers with the US Department of Energy (DOE)’s Joint BioEnergy Institute (JBEI) and the US Department of Agriculture’s Agricultural Research Service (ARS), have demonstrated that introducing a maize (corn) gene into switchgrass (Panicum virgatum), a potential feedstock for advanced biofuels, more than doubles (250%) the amount of starch in the plant’s cell walls, resulting in higher glucose release for fermentation with or without biomass pretreatment.

The gene, a variant of the maize gene known as Corngrass1 (Cg1), holds the switchgrass in the juvenile phase of development, preventing it from advancing to the adult phase. The results of this research are described in an open access paper published in the Proceedings of the National Academy of Sciences (PNAS).

Chuck
Biofuel properties and digestibility of Cg1-augmented switchgrass. (A) Saccharification assay using dilute base pretreatment of field grown leaves of wild type and three classes of transformants. (B) Potassium iodide staining of upper nodes of field grown stems of Cg1 (Left) and wild type (Right). (C) Starch measurements of field grown stems of wild type and two independent transformants of each class. (D) Saccharification assay of stems and leaves of wild type and two independent weak transformants without biomass pretreatment after 24 h of digestion. (E) Saccharification assay over 72 h of stems of two field grown wild-type plants and two weakly expressing transformants using method I without pretreatment. (F) Saccharification assay over 72 h of stems of two field grown wild-type plants and two weakly expressing transformants using method II without pretreatment. Chuck G S et al. PNAS 2011;108:17550-17555.
Click to enlarge.

Plant biomass can be broken down to monosaccharides (saccharification) and converted to fuels. Plant cell walls are composed of cellulose microfibrils embedded in a cross-linked network of matrix polysaccharides and copolymerized with lignin. This complex structure inhibits the saccharification of cell wall polysaccharides by cell wall degrading enzymes. Furthermore, byproducts of the harsh pretreatments necessary to enable saccharification inhibit growth of microorganisms used to produce biofuels. Therefore, improving saccharification efficiency is one of the major goals in developing an efficient, cost-effective biofuel industry.

...Plants go through a series of development stages over time in response to a variety of stimuli, both external and internal. Each phase displays unique morphological and physiological characteristics that change when the plant undergoes a transition to the next phase. One such developmental transition is the switch from the juvenile to adult phase of development. In general, juvenile plant material is less lignified and displays differences in biomass accumulation and character. These juvenile traits may reduce the recalcitrance of biomass to conversion into fermentable sugars. By controlling the genes that regulate the juvenile to adult phase transition in plants, it may be possible to modify or enhance the biomass properties of a wide range of bioenergy feedstocks.

The dominant maize Corngrass1 (Cg1) mutant fixes plant development in the juvenile phase and affects both biomass accumulation and saccharification efficiency. Cg1 mutants increase biomass due to continuous initiation of axillary branches (tillers) and leaves. The resulting biomass has reduced adult characteristics and ectopic juvenile cell identities. In addition, Cg1 mutant leaves contain decreased amounts of lignin and increased levels of glucose and other sugars compared with wild type, which could provide an improved substrate for saccharification.

—Chuck et al.

Lignocellulosic biomass is the most abundant organic material on earth. Studies have consistently shown that biofuels derived from lignocellulosic biomass could be produced in the United States in a sustainable fashion and could replace today’s gasoline, diesel and jet fuels on a gallon-for-gallon basis. Unlike ethanol made from grains, such fuels could be used in today’s engines and infrastructures and would be carbon-neutral, meaning the use of these fuels would not exacerbate global climate change.

Among potential crop feedstocks for advanced biofuels, switchgrass offers a number of advantages. As a perennial grass that is both salt- and drought-tolerant, switchgrass can flourish on marginal cropland, does not compete with food crops, and requires little fertilization.

The original Cg1 was isolated in maize about 80 years ago. We cloned the gene in 2007 and engineered it into other plants, including switchgrass, so that these plants would replicate what was found in maize. The natural function of Cg1 is to hold pants in the juvenile phase of development for a short time to induce more branching. Our Cg1 variant is special because it is always turned on, which means the plants always think they are juveniles.

—George Chuck, lead author, with joint appointments at ARS and UC Berkeley

Chuck and his colleague Sarah Hake, another co-author of the PNAS paper and director of the Plant Gene Expression Center, proposed that since juvenile biomass is less lignified, it should be easier to break down into fermentable sugars. Also, since juvenile plants don’t make seed, more starch should be available for making biofuels. To test this hypothesis, they collaborated with Simmons and his colleagues at JBEI to determine the impact of introducing the Cg1 gene into switchgrass.

In addition to reducing the lignin and boosting the amount of starch in the switchgrass, the introduction and overexpression of the maize Cg1 gene also prevented the switchgrass from flowering even after more than two years of growth, an unexpected but advantageous result. The lack of flowering limits the risk of the genetically modified switchgrass from spreading genes into the wild population, says Chuck.

The results of this research offer a promising new approach for the improvement of dedicated bioenergy crops, but there are questions to be answered. For example, the Cg1 switchgrass biomass still required a pre-treatment to efficiently liberate fermentable sugars.

The alteration of the switchgrass does allow us to use less energy in our pre-treatments to achieve high sugar yields as compared to the energy required to convert the wild type plants. The results of this research set the stage for an expanded suite of pretreatment and saccharification approaches at JBEI and elsewhere that will be used to generate hydrolysates for characterization and fuel production.

—Blake Simmons, head of JBEI’s Deconstruction Division

Another question to be answered pertains to the mechanism by which Cg1 is able to keep switchgrass and other plants in the juvenile phase.

Co-authoring the PNAS paper with Chuck and Simmons were Christian Tobias, Lan Sun, Florian Kraemer, Chenlin Li, Dean Dibble, Rohit Arora, Jennifer Bragg, John Vogel, Seema Singh, Markus Pauly and Sarah Hake.

This research was supported in part by DOE’s Office of Science and by the USDA-ARS. JBEI is one of three Bioenergy Research Centers established by the DOE’s Office of Science in 2007. It is a scientific partnership led by Berkeley Lab and includes the Sandia National Laboratories, the University of California campuses of Berkeley and Davis, the Carnegie Institution for Science, and the Lawrence Livermore National Laboratory.

Resources

  • George S. Chuck, Christian Tobias, Lan Sun, Florian Kraemer, Chenlin Li, Dean Dibble, Rohit Arora, Jennifer N. Bragg, John P. Vogel, Seema Singh, Blake A. Simmons, Markus Pauly, and Sarah Hake (2011) Overexpression of the maize Corngrass1 microRNA prevents flowering, improves digestibility, and increases starch content of switchgrass. PNAS 108 (42) 17550-17555 doi: 10.1073/pnas.1113971108

Comments

HarveyD

Introducing this gene into humans could end up with 10+B long lasting juveniles? It would be interesting to come back in 100 years or so to see how many are still alive.

SJC

When you can get 10 tons per acre per year just gasify it and create that high octane gasoline from DME.

HarveyD

Yes, longer lasting juvenile grass could produce more if it is reproductive during that stage. The fact that it doesn't flower or produce seeds is ideal for whoever markets it. Growers will become captive of whoever has the patent rights.

Bob Wallace

Switchgrass is a native of the American prairie. It evolved on the sort of marginal land where we might want to grow it.

Switchgrass also fixes (sequesters) a large amount of carbon underground due to a very extensive and deep root system. It can be grown on "used up" farmland such as burned out cotton fields to bring the soil back up to crop production levels.

Bands of switchgrass could be grown between fields of other crops as a way to trap runoff fertilizer and topsoil.

Growers will have to buy the seed only once since it's a perennial.

SJC

good points

Treehugger

Well, I am wondering if the plant will keep its robustness and ability to grow in marginal land as well as its perennial character once you have introduce a gene like this one that tries to boost its sugar production yield. Maybe it will but that is to be shown. Boosting the yield of a plant is often obtained at the expense of its robustness. But like you say there might use of it to as trap for runoff fertilizer.

HarveyD

BW...industry will certain find ways to make it an annual type plant to ensure higher profits.

Chops

HarveyD....If you don't like it, don't buy it. Keep planting the native variety and get the native plant yields.

SJC

Until the GM pollen is blown into the native fields and Monsanto sues the farmers for patent violations.

msevior

This will get grown as soon as there is demand for it. Which of the next-gen biofuel companies is ready to start pilot production with switch-grass as feedstock?

Reel$$

It's good to see progress in biofuels which will play a role in transition from oil. Most GM plant types are annuals - forcing farmers to buy new seed. This is questionable. If the patent holder wants to squeeze more $$ out of their product sell growers a 5 year fixed perennial at higher cost. This saves the whole reseed process over the license period.

HarveyD

chops....that's how the USA and many other countries got into the mess we"re in now.

HarveyD

Reel$$ burning bio-fuels to move a vehicle is still an antic way to transport passengers and cargo. We will have to wean ourselves from that acquired unhealthy inefficient habit.

Electric trains + e-tractors at each end can move cargo faster and more efficiently.

Electrified road vehicles can move passengers much more efficiently.

Improved ICEVs are a lure promoted and paid for by the oil/liquid fuel industries.

Bob Wallace

"Improved ICEVs are a lure promoted and paid for by the oil/liquid fuel industries."

I'd say that more efficient ICEVs are an attempt by ICEV manufacturers to hold on to market share.

That's not a bad thing. If we can cut our oil use significantly through efficiency that both stretches our oil supply and reduces atmospheric CO2.

The only down side is that it could slow the growth of EVs and, from the way I understand it, the price of EVs is due to low manufacturing volumes.

If we could get the price of EV batteries down to where it is expected they will settle the ICEV should start a rapid disappearance.

One of the Texas utility companies has just moved to a three stage TOU billing system with nighttime rates set at $0.068/kWh. Driving a Honda Fit EV that uses 0.35kWh/mile means a per mile cost of $0.024/mile.

Driving a 35MPG Honda Fit on $4/gallon gasoline will cost $0.114/mile.

Who, besides someone who often drives more than 120 miles per day, is going to buy the model that costs five times as much per mile to operate?


Bob Wallace

"Improved ICEVs are a lure promoted and paid for by the oil/liquid fuel industries."

More likely improved ICEVs are a response to increased MPG requirements.

Car manufacturers are responding to the reality of higher fleet mileage requirements. They're working to increase mileage for their liquid fuel fleets and they are working to bring affordable EVs to market.

I'm sure there are individuals within car companies who love the internal combustion engine and will work hard to make it as efficient as possible in order to keep it viable as long as possible. But that's OK. They'll stretch our oil supply and cut CO2 emissions through their efforts.

And improvements in vehicle weight and aerodynamics will benefit EVs as well as ICEVs.

The oil/liquid fuel industries are more likely spending their money funding FUD about EVs. Just like the coal industry spends money spreading FUD about renewable energy.

Reel$$

I expect the PHEV to play a major role in electrification. The Prius will likely set the near term sales record for plug-in vehicles. Despite its paltry AER, consumers trust and like the Prius and the plug-in version will be their baby step to full BEV.

Toyota now claims sales of 3 Million Prii, in 70 countries. All these owners are potential PHEV customers.

Bob Wallace

I also expect the PHEV to play a major role in electrification.

Right up to the point where we get ~200 mile range EVs at a price comparable to their PHEV counterparts.

At that point I expect the ICE to go the way of the carburetor.

I don't think it's going to be possible to build a small fuel engine as cheaply as the batteries which will replace it. And with V2G the extra batteries are going to be profit centers for EV owners.

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