Supercharged Photosynthesis Advanced Genetic Tools Could Help Boost Crop Yields and Feed Billions More People

Supercharged Photosynthesis Advanced genetic tools could help boost crop yields and feed billions more people. Availability: 10-15 years by Kevin Bullis In December, geneticists announced that they’d made a major advance in engineering rice plants to carry out photosynthesis in a more efficient way—much as corn and many fast-growing weeds do. The advance, by a consortium of 12 laboratories in eight countries, removes a big obstacle from scientists’ efforts to dramatically increase the production of rice and, potentially, wheat. It comes at a time when yields of those two crops, which together feed nearly 40 percent of the world, are dangerously leveling off, making it increasingly difficult to meet rapidly growing food demand. Supercharged Photosynthesis BreakthroughEngineering rice plants to extract energy from sunlight far more efficiently than they do now. Why It MattersCrop yields aren’t increasing fast enough to keep up with demand from a growing population. Key PlayersPaul Quick, International Rice Research Institute Daniel Voytas, University of Minnesota Julian Hibberd, University of Cambridge Susanne von Caemmerer, Australian National University The supercharged process, called C4 photosynthesis, boosts plants’ growth by capturing carbon dioxide and concentrating it in specialized cells in the leaves. That allows the photosynthetic process to operate much more efficiently. It’s the reason corn and sugarcane grow so productively; if C4 rice ever comes about, it will tower over conventional rice within a few weeks of planting. Researchers calculate that engineering C4 photosynthesis into rice and wheat could increase yields per hectare by roughly 50 percent; alternatively, it would be possible to use far less water and fertilizer to produce the same amount of food. The December results, achieved by the C4 consortium and led by Paul Quick at the International Rice Research Institute (IRRl) in the Philippines, introduced key C4 photosynthesis genes into a rice plant and showed that it carried out a rudimentary version of the supercharged photosynthesis process. “It’s the first time we’ve seen evidence of the C4 cycle in rice, so it’s very exciting,” says Thomas Brutnell, a researcher at the Danforth Plant Science Center in St. Louis. Brutnell is part of the C4 Rice Consortium headed by IRRI, which has funding from the Bill & Melinda Gates Foundation, but was not directly involved in the most recent breakthrough. Despite the genetic changes, the altered rice plants still rely primarily on their usual form of photosynthesis. To get them to switch over completely, researchers need to engineer the plants to produce specialized cells in a precise arrangement: one set of cells to capture the carbon dioxide, surrounding another set of cells that concentrate it. That’s the distinctive wreath anatomy found in the leaves of C4 plants. However, scientists still don’t know all the genes involved in producing these cells and suspect that they could number in the dozens. New genome editing methods that allow scientists to precisely modify parts of plant genomes could help solve the problem. Using conventional breeding to manipulate more than one or two genes is a “nightmare,” Brutnell says, let alone trying to engineer a plant with dozens of gene changes. Genome editing could make it possible to change a large number of genes easily. Says Brutnell: “Now we have the toolbox to go after this.” It can be a decade or more before even simple crop modifications reach farmers, let alone changes as complex as reëngineering how plants carry out photosynthesis. But once scientists solve the C4 puzzle in a plant such as rice, they hope, the method can be extended to dramatically increase production of many other crops, including wheat, potatoes, tomatoes, apples, and soybeans. Hydrogen from Algae Genetically modified algae could be efficient producers of hydrogen and biofuels. by Prachi Patel Algae are a promising source of biofuels: besides being easy to grow and handle, some varieties are rich in oil similar to that produced by soybeans. Algae also produce another fuel: hydrogen. They make a small amount of hydrogen naturally during photosynthesis, but Anastasios Melis, a plant- and microbial-biology professor at the University of California, Berkeley, believes that genetically engineered versions of the tiny green organisms have a good shot at being a viable source for hydrogen. Algae power: While regular green algae absorb most of the light falling on them (right), algae engineered to have less chlorophyll let some light through (left). When grown in large, open bioreactors in dense cultures, the chlorophyll-deficient algae will let sunlight penetrate to the deeper algae layers and thereby utilize sunlight more efficiently. Melis has created mutant algae that make better use of sunlight than their natural cousins do. This could increase the hydrogen that the algae produce by a factor of three. It would also boost the algae’s production of oil for biofuels. The new finding will be important in maximizing the production of hydrogen in large-scale, commercial bioreactors. In a laboratory, Melis says, “[we make] low-density cultures and have thin bottles so that light penetrates from all sides.” Because of this, the cells use all the light falling on them. But in a commercial bioreactor, where dense algae cultures would be spread out in open ponds under the sun, the top layers of algae absorb all the sunlight but can only use a fraction of it. Melis and his colleagues are designing algae that have less chlorophyll so that they absorb less sunlight. That means more light penetrates into the deeper algae layers, and eventually, more cells use the sunlight to make hydrogen. The researchers manipulate the genes that control the amount of chlorophyll in the algae’s chloroplasts, the cellular organs that are the centers for photosynthesis. Each chloroplast naturally has 600 chlorophyll molecules. So far, the researchers have reduced this number by half. They plan to reduce the size further, to 130 chlorophyll molecules. At that point, dense cultures of algae in big bioreactors would make three times as much hydrogen as they make now, Melis says. “If you can increase the productivity by means of thinning out the [chlorophyll], it’s going to affect any product that you make,” says Rolf Mehlhorn, an energy technologist at the Lawrence Berkeley National Laboratory. Algae that use sunlight more effectively would produce more oil, he says. Startups such as Solix Biofuels, based in Fort Collins, CO, and LiveFuels, based in Menlo Park, CA, are trying to extract oil from algae; the oil can be refined to make diesel and jet fuel. The process is still at least five years from being used for hydrogen generation. Researchers will first have to increase the algae’s capacity to produce hydrogen. During normal photosynthesis, algae focus on using the sun’s energy to convert carbon dioxide and water into glucose, releasing oxygen in the process. Only about 3 to 5 percent of photosynthesis leads to hydrogen. Melis estimates that, if the entire capacity of the photosynthesis of the algae could be directed toward hydrogen production, 80 kilograms of hydrogen could be produced commercially per acre per day. Switching 100 percent of the algae’s photosynthesis to hydrogen might not be possible. “The rule of thumb is, if we bring that up to 50 percent, it would be economically viable,” Melis says. With 50 percent capacity, one acre of algae could produce 40 kilograms of hydrogen per day. That would bring the cost of producing hydrogen to $2.80 a kilogram. At this price, hydrogen could compete with gasoline, since a kilogram of hydrogen is equivalent in energy to a gallon of gasoline. In 2000, Melis, working with researchers at the National Renewable Energy Laboratory (NREL), found that depriving the algae of sulfur nutrients forced the cells to make more hydrogen. The researchers were only able to deprive the algae of sulfur for a few days at a time, but during that time, about 10 percent of the algae’s photosynthetic capacity went toward making hydrogen. Researchers at NREL are making progress in increasing hydrogen-production efficiency, according to lead researcher Michael Seibert. They can now force the algae to generate hydrogen for up to three months, as opposed to just a few days. Seibert expects that Melis’s chlorophyll-trimmed algae will be useful when the process is transferred to large bioreactors. Until the NREL researchers test the mutant algae, though, he says that it may be too early to tell. Name:___________________________________ Period:__________ Engineering with Photosynthesis 1. Explain this new discovery. 2. What does photosynthesis have to do with this discovery? 3. Represent this technology in a drawing. 4. Who are the scientists behind this discovery? 5. How do you think this discovery could affect the people of the world? 6. What could change in our community with this discovery? 7. Explain why your life might change because of this discovery. 8. Do you see any problems with this new technology? .

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