July 2011

Pouring energy into biofuels

Learning about biofuels in Brazil

The American Society for Biochemistry and Molecular Biology is playing a vital role in creating the next generation of biofuels. Last fall, the society co-sponsored a week-long advanced course aimed at inspiring interested graduate students and postdoctoral fellows to join the biofuels revolution. At a small resort in the lush coastal city of Ubatuba, Brazil, 40-odd international participants gathered to attend lectures and participate in intense roundtable discussions.

The aim wasn’t to have attendees listen to endless talks, says Bettie Sue Masters, past president of ASBMB and principle organizer of the school. “It was really interactive,” she says. In the daily roundtable sessions, participants had the chance to discuss their own work or research aspirations or to solicit lecturers’ career advice.

Besides being a terrific chance for young researchers to learn about this burgeoning field, it also proved to be a great way to forge a strong partnership between ASBMB and colleagues in the Brazilian Society for Biochemistry and Molecular Biology and the International Union of Biochemistry and Molecular Biology. These groups are planning to cosponsor future meetings, including one in the fall of 2012 on protein folding and protein-protein interactions.

“It was much better than we ever thought it would be – a valuable experience for everyone involved,” Masters says.

However, ethanol also has a number of drawbacks. Crops used most often to produce it can be finicky about where they’ll grow. For example, sugarcane, another common source for ethanol, thrives in Florida but not in Michigan, and corn needs rich, pampered soil and not rocky, arid land. Additionally, since the most common sources of ethanol also are food for people, it sets up a competition over the best land between food and fuel.

“It could lead to an unstable market,” says Dominique Loque, a research scientist at the Joint BioEnergy Institute in Emeryville, Calif. “Only rich people will be able to drive and eat.”

Consequently, many researchers have suggested gathering energy from the vegetative tissues of plants instead of the parts we use for food. Stems, branches, and leaves contain cellulose, a polymer of glucose in the cell wall that holds ample energy for conversion to biofuels. Indeed, potential energy in cellulose is often more than 10 times that available in starch from a given plant. Moreover, these plant organs are frequently a throw-away byproduct of the food industry, so conversion to biofuels could prevent waste.

However, notes Bush, switching from corn kernels to foliage isn’t so simple. Though researchers have actively worked on improving corn and other food plants for hundreds of years, the focus has been on the seed, not the greenery. As a result, about half of corn’s above-ground biomass is in its ears. If the new biofuel focus is the rest of the plant, Bush says, researchers better get cracking on making new energy crops, such as grasses— significantly bigger.

That’s one of his lab’s projects. With colleagues at Colorado State University and the International Rice Research Institute in the Philippines, Bush is working on identifying genes that are responsible for making the most of rice’s green biomass. Rice is a good model for improving other grasses’ biomass, he says, since the genomes of all 20 rice varieties have been sequenced. Bush notes that in this work, rice is an experimental model and not a target as a biofuel crop.

“A long time ago, many breeders learned that if you see a very large plant, 50 percent larger than the others, to just ignore it— they put most of their carbon into vegetative growth and have lower seed production,” he says. But those big plants are just what he and his colleagues are looking for. The researchers have spent many days walking through rice fields searching for the largest plants produced either through hybrid crosses or mutagenesis. Using modern deep sequencing approaches, Bush and his colleagues can then locate the gene responsible for the plants’ extraordinary size. The team is now close to identifying the first promising gene from that approach.

Bush’s lab also is working on another way to make more greenery through bypassing the feedback system that controls a plant’s photosynthesis rate. Leaves are the hotbed for photosynthesis, and as plants spin sunlight into sucrose, that product is transported to non-photosynthetic tissues in the plant’s vascular system. If production exceeds export, Bush explains, plants shut off photosynthesis until the sweet stuff can distribute to other parts of the plant through its vascular system. Using sugarbeet as a model system, he and his colleagues have engineered plants whose cells have a sucrose transport gene placed behind a constitutively active promoter. Consequently, the leaves are constantly pumping out sucrose— and thus, keeping low sucrose in the leaves and preventing negative feedback on photosynthesis. Over a season, he hypothesizes, this furious activity translates into significantly more biomass per plant.

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