SCIENCE & TECHNOLOGY
Monsanto, for example, is in common corn crops, the final stage of genetically engineered commercializing drought-tolerant varieties remain vibrant drought-tolerant even when water is in corn. Earlier this short supply. summer, in collaboration with Germany-based BASF, Monsanto issued a statement disclosing the identity of the gene that will lie at the heart of what the companies are calling the world’s first biotechnology-derived (meaning genetically engineered) droughttolerant crop. The companies say the product will enhance yields relative to common varieties of corn by some 10% in areas prone to the kind of moderate drought faced by western Nebraska. That region tends to get less rainfall than eastern parts of the Corn Belt. The biotech product is targeted for release in about two years. Other companies, including Syngenta and DuPont, are also gearing up to sell drought-tolerant varieties of corn. Several other crops including rice, wheat, soy, canola, sunflower, and cotton are also being studied by various agribusiness companies that aim to improve yields of those crops during dry spells.
MO N SAN TO
DROUGHT? WHAT DROUGHT? Unlike
GETTING BY ON LITTLE WATER Advances in breeding and basic science confer DROUGHT TOLERANCE to crops MITCH JACOBY, C&EN CHICAGO
ACCORDING TO the witty accusation
often attributed to Mark Twain, everyone talks about the weather, but no one does anything about it. Scientists still may not be able to do anything about the weather, but they are working to make plants that thrive despite it. By probing the biological and chemical bases of some plants’ innate ability to flourish in regions and periods of limited precipitation, researchers in industry, academia, and government labs are learning to confer drought tolerance to major food, feed, and fiber crops including rice, corn, and cotton. These scientific advances, which have been mounting in recent months, come as the combined effects of surging world population and climate change may be poised to deliver a potent one-two punch to global food supplies in the coming years. According to estimates by the United Nations’ Food & Agriculture Organization (FAO), by 2030, the world’s farmers will need to grow 30% more grain than they do currently to feed a projected global population of 8.3 billion people. Coupled with predictions by FAO and the National Oceanic & Atmospheric Administration of more frequent and more intense dry spells in the years ahead, increasing agricultural
output to meet global needs is going to be a tough challenge. Farming more land isn’t an option. “There really isn’t any additional arable land being brought into production nowadays, and there are few places in the world where you could even look to find such land,” says David A. Fischhoff, vice president for technology strategy and development at agriculture technology company Monsanto. “We need to live with the footprint we have and at the same time produce enough food to feed the world’s growing population,” he adds. Robert Berendes, head of business development at Switzerland-based Syngenta, points out that economic growth further increases the challenge. As per capita income increases, as is happening in China, for example, demand for food—and in particular meat, which depends on animal feed— increases faster than population. “So we need to produce more food using the same amount of land but with reduced amounts of water,” Berendes says. For that reason, researchers in various organizations are focusing on developing plants that produce ample yields even when water is scarce. MORE ONLINE WWW.CEN-ONLINE.ORG
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TO AGRONOMISTS, drought refers to a
water shortage that causes stress in a given crop. A severe drought will destroy any crop. But even a moderate lack of water can stress a plant. Corn, for example, may show effects of moderate water shortage through wilting, loss of leaves, a decrease in the size and number of kernels per ear, or a decrease in the number of ears raised per acre. Many generations of breeders have slowly improved crop varieties, by crossing (mating) pairs of plants that exhibit certain characteristics, such as high yield under ideal conditions and strong stalks under dry conditions; waiting for the “offspring” to mature; and then selecting the ones with the best traits for the next round of mating. That traditional approach to breeding, which is slow and labor intensive, is giving way to much faster breeding techniques supported by molecular biology, Berendes says. By examining plant DNA in search of telltale signs of traits before breeding, researchers can now predict which crosses are most likely to be successful, thereby dramatically saving time.
To learn about the instruments that facilitate research in crop analytics, click on this story at www.cen-online.org. SEPTEMBER 28, 2009
Even so, thousands of experimental lines of plants are bred and tested under controlled conditions in Monsanto’s drought-tolerance program, according to Robert S. Reiter, who serves as the company’s vice president of breeding technology. “It’s like looking at an enormous number of combinations of naturally occurring corn genes and searching for ones that have the best ability to tolerate drought,” he explains. But even with all the cross-breeding, some genetic variations that could further enhance corn’s ability to stand up to dry growing conditions still won’t be found in corn’s gene pool. That’s where genetic engineering comes in. Monsanto and BASF found that a gene first identified in bacteria that were stressed by subjecting them to cold temperatures can help plants tolerate stress induced by drought. That gene is cspB, from Bacillus subtilis. It codes for a cold-shock protein that acts as an RNA chaperone.
Such chaperones bind to and assist RNA in carrying out its basic biological functions by correcting misfolded forms of RNA. That bacterial gene has been inserted into the companies’ drought-tolerant corn. Normally when a plant undergoes some kind of stress, it starts to “hunker down, shut off fundamental processes, and conserve resources,” Reiter says. In contrast, corn enhanced with the drought-tolerance gene remains in a more normal metabolic state when water is scarce. Reiter notes that years of controlled field tests have shown a yield enhancement relative to corn lacking the extra gene of about 6–15%, depending on the year and drought intensity. Importantly, however, that stress tolerance does not lead to a decrease in crop productivity when the plants are well watered, he adds. Unlike corn, sorghum tolerates drought well naturally. That cereal species feeds millions of people mainly in developing
PLA N T B R E E D ING
Norman E. Borlaug, the father of the green revolution of the 1950s and 1960s that brought advanced breeding and agricultural practices to developing countries and rescued them from drought-induced famine, died earlier this month. Borlaug is widely credited with saving hundreds of millions of lives. He was the Distinguished Professor of International Agriculture at Texas A&M University and the recipient of the 1970 Nobel Peace Prize. After completing doctoral studies in plant pathology in the 1940s, Borlaug, who was a farm boy from Iowa, began conducting research in Mexico at the institute that later came to be known as the International Maize & Wheat Improvement Center.
TEXAS A&M
Crop Expert Saved Millions From Drought
Borlaug, 1914–2009 One of his main strategies was cross-breeding tall tropical wheat varieties that thrived and were more productive than other types of wheat in favorable growing conditions—but which buckled under the weight of their ample seeds—with shorter “dwarf” wheat plants that were sturdy enough to support large yields of heavy kernels. Borlaug’s efforts
paid off handsomely. After breeding many thousands of plants, he produced sturdy shortstalked wheat varieties that were high-yielding and resistant to common plant diseases. Those plant varieties produced three to four times higher grain yields than common varieties at that time. Using Borlaug’s new strains, Mexico, which had been importing 60% of its wheat in the 1940s, became self-sufficient by the mid-1950s. The breeding expert’s efforts in famine-stricken India and Pakistan in the 1960s led those nations, too, to self-sufficiency within a few years. Eventually, Borlaug’s breeding strategies and wheat varieties were imported to Central and South America, the Middle East, and Africa.
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SEPTEMBER 28, 2009
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SCIENCE & TECHNOLOGY
countries and is used to make biofuel in the U.S. It originates from Africa and is well adapted to growing in arid climates. Details of sorghum’s knack for thriving in hot, dry weather aren’t fully understood. But earlier this year, a large team of researchers led by plant geneticist Andrew H. Paterson of the University of Georgia, Athens, took a key step toward uncovering the biochemical basis of sorghum’s inherent drought tolerance by determining and analyzing sorghum’s complete genome sequence and comparing it with other plants’ (Nature 2009, 457, 551).
acting enzyme that enables plants to take up atmospheric CO2 through pores known as stomata faster than C3 varieties. When the pores open to allow CO2 to diffuse in and O2 to diffuse out, water also escapes from the plant. The upshot is that C4 plants keep their stomata closed more of the time than C3 plants do and thereby efficiently ACCORDING TO the team, sorghum’s minimize water loss—an important survival extra copies of certain genes coupled with trick for plants growing in arid conditions. its unusual photosynthetic pathway may Direct chemical methods for mitigating play key roles in the plant’s overall drought the effects of drought are also in the works. response. Specifically, compared with the One example, based on the properties of relatively small rice genome, sorghum has 1-methylcyclopropene, is being developed four additional copies of a certain regulatojointly by Syngenta and AgroFresh, a Dow ry gene that activates other subsidiary. Ordinarily, genes when stressed by crops exposed to drought O OH drought. Sorghum also conand other types of stress tains a surplus of hydrogenproduce ethylene, which OH O bond-breaking enzymes triggers a number of negaknown as expansins that tive responses including are believed to be linked to wilting, reduced photosyn(+)-Abscisic acid plant durability. thesis, and poor pollinaFurthermore, photosyntion. The companies say thesis in sorghum proceeds by that treating stressed corn, cereBr way of the C4 pathway, so called als, and other crops with Invinsa, because the process initially coma soon-to-be-released product bines CO2 with a three-carbon based on 1-methylcyclopropene, compound to make a C4 molecule protects the plants from the efO S O (oxaloacetic acid). Corn, which fects of moderate drought. They is a distant relative of sorghum, is explain that the compound binds NH also a C4 plant. In contrast, rice, to the plants’ ethylene receptors, wheat, and most other plants dethereby blocking ethylene from N pend on C3 photosynthesis, which transmitting the stress signals. incorporates CO2 to make a threeAbscisic acid is another plant carbon compound in the first step. hormone that may lie at the cenPyrabactin The C4 process involves a fastter of future drought-protection
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CEREAL SEQUENCING
Analyzing sorghum’s recently sequenced genome may offer clues to enhancing drought tolerance in a variety of plants.
treatments for crops. For years, researchers have known that when plants dry up or are exposed to cold, levels of abscisic acid in leaves soar. The rising concentration of abscisic acid inhibits plant growth, conserves water, and generally signals plants to slow down, which helps them cope with adverse growing conditions. Applying abscisic acid directly to farm crops isn’t an option because the compound is expensive and sensitive to light. So researchers have tried to tease out the molecular basis of abscisic acid’s action to find suitable chemical treatments that can protect crop yields in the face of drought. Earlier this year, a team of researchers led by University of California, Riverside, plant biologist Sean R. Cutler reported in Science the discovery of such a molecule (2009, 324, 1068). The group found that pyrabactin, a stable synthetic sulfonamide, turns on the abscisic acid signaling pathway in the plant Arabidopsis thaliana, a widely studied model organism. Cutler explains that abscisic acid and its mimic, pyrabactin, trigger the signaling process by binding to a protein called PYR1, which in turn binds to and inhibits the action of a phosphatase enzyme. A half century ago, advances in breeding led to enormous boosts in grain yields, bringing self-sufficiency to developing countries. Labeled the green revolution, those agricultural practices enabled food production to keep pace with worldwide population growth. Since then, crop yields have increased dramatically, but so has population—and it continues to grow. To meet skyrocketing food-production needs, scientists such as Monsanto’s Fischhoff are working to double yields in the U.S. of key crops such as corn by 2030 relative to yields in 2000. The strategy, he says, is to continue improving plant traits such as drought tolerance through further advances in breeding, biotechnology, and agronomic practices. “It’s a tall order,” Fischhoff admits, “but I think it’s an achievable goal.” ■
