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Sugar Genes Make Rice Crops Sturdier

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PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES
The importance of rice as a crop--it currently feeds half the world's population--has fueled scientific attempts to improve yields of the plant. Earlier this year, two international teams published draft sequences of the genomes of two of the most abundant types of rice. Now results published online this week by the Proceedings of the National Academy of Sciences suggest that scientists have successfully produced a genetically modified form of rice that can survive drought, high salinity and temperature changes better than its traditional counterparts can.

Ajay K. Garg of Cornell University and his colleagues modified strains of Indica rice, which is common throughout Asia, to produce a sugar known as trehalose. Although the simple sugar is common in many bacteria and insects, few plants manufacture the molecule. Those that do, however, are classified as "resurrection" plants because of their ability to survive long periods without water and revive quickly once moisture becomes available. Previous attempts to introduce trehalose-producing genes into rice resulted in plants that were less hardy than natural plants were. In the new work, the scientists first fused two genes from E. coli that synthesize the sugar and then introduced them, together with so-called promoter sequences, into the plant. These sequences allowed the researchers to control when and where the introduced genes expressed themselves. For instance, the leaf of a plant may produce trehalose, while the edible grains do not. Overall, the plants carrying the sugar-producing genes not only fared better under stressful conditions but also displayed more efficient photosynthesis under normal circumstances. (The image above shows rice plants after exposure to drought conditions. The plant on the left is transgenic.)

Despite the encouraging findings, trehalose-containing rice will not be planted outside a laboratory for at least a few years. "We still have a lot to learn about trehalose in important crop plants," Garg notes. But if the plants are judged safe and large-scale production is feasible, the modified rice could help to feed the world's burgeoning population. Says study co-author Ray J. Wu, "Anything we can do to help crop plants cope with environmental stresses will also raise the quality and quantity of food for those who need it most."

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