Gains in grain: Better rice growth - through science

EAST LANSING - Tao Sang and his colleagues have spent hundreds of hours shaking rice plants. Shaking them, that is, in the name of science. Sang is professor of plant biology at Michigan State University and the leader of a research team that has identified the genetic mutation that keeps rice grains from falling off their stalks. The results of their five-year research project, which could help to increase rice harvests - and feed more people around the world - made the cover of Friday's issue of Science, arguably the world's leading scientific journal. As genetic mutations in rice go, the one that Sang and his colleagues have found has been singularly important for human life, because it's responsible for the changes that made rice cultivation worthwhile starting thousands of years ago. Strengthening seeds The rice that sits on supermarket shelves today is descended from wild grasses, which shed their seeds fairly easily, Sang said. That helps the wild varieties spread their populations, and helps ensure the survival of the species. But it doesn't help farmers who need rice plants that hang onto their seeds at least long enough for those seeds to be harvested. That's where the mutation comes in. When humans began cultivating rice nearly 10,000 years ago, they favored plants that would hang onto their mature grains - plants that had a homozygous recessive genotype at chromosomal location sh4. For Sang and his collaborators, research associate Changbao Li and graduate student Ailing Zhou, identifying that single genetic change was an arduous process, requiring them to isolate the DNA of about 12,000 seedlings, to cross reference individual plants' genetic markers with the degree to which they hold onto their seeds. "Even when we narrowed it down to one chromosome region, which still includes hundreds of genes, we needed to chop, chop, chop it into really small pieces to look at where the recombination occurred," Sang said. Innovative blueprint Two innovations sped the process along. One was the fact that Li developed a new, faster method of DNA isolation. Sang estimates it cut at least a year off the project. The other was the mapping of the rice genome, completed last summer by a group of international scientists, which gave the MSU group a blueprint with which to work. The mutation they identified produces a kind of protein called a "transcription factor," that makes its way into the nuclei of a plant's cells and sets off a series of other changes. The changes center around what's known as the "abscission layer," a barrier of thin-walled cells that develops along the base of the grain as it ripens and ultimately serves as the breaking point separating the grain from the plant. In rice plants that have the mutation, abscission layers form incompletely, which helps the mature grains hang onto the plant longer. "With better knowledge of this abscission pathway, which is very poorly known, there's the possibility of using biotechnology to optimize separation of the fruits and grains, to optimize the amount of labor (in harvesting) and minimize the loss of fruits," Sang said. Optimizing the harvest In rice, it could help scientists optimize different plants to different styles of harvesting, minimizing harvest losses for a crop that feeds more than half the world's population. Ronald Phillips, director of the Center for Microbial and Plant Genomics at University of Minnesota, studies the genetics of shattering in American wild rice, a species that is still hard to cultivate because it drops its seeds very easily. Phillips said the impact of this sort of research could be "tremendous," particularly for his state's wild rice farmers, who can lose a year's profits with one bad wind storm. The potential impact doesn't end there. Because rice is genetically similar to other cereal crops, such as wheat and barley, the research could be applied much more broadly. "Once you have it in one, you can begin to look for the same gene sequences in other crop plants," said Richard Triemer, chairman of the MSU Plant Biology Department. "It has implications well beyond rice, though rice alone is enough. It feeds most of the world." "Source":[ http://www.checkbiotech.org/root/index.cfm?fuseaction=news&doc_id=12555&start=1&control=207&page_start=1&page_nr=101&pg=1].

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