Monday, September 5, 2000
WRITER: Phil Williams, 706/542-8501, [email protected]CONTACT: Susan Wessler, 706/542-1870, [email protected]
UNIVERSITY OF GEORGIA RESEARCHERS TO LEAD $3.4 MILLION NATIONAL SCIENCE FOUNDATION PROJECT ON GENETICS OF RICE
ATHENS, Ga. -- The National Science Foundation has awarded a grant of $3.4 million to a team led by a University of Georgia botany professor for research into the role of transposable elements in rice.
The new research will be on the cutting edge of studies in the genetics of rice and could help lead to a new understanding of the world's number-one crop plant.
Transposable elements are mobile fragments of DNA that can move from one chromosomal location to another and increase their contribution to the whole genome until they can account for the majority of the genomic DNA. For years, scientists thought that these elements were "junk" and had no real function in the genomes of plants or animals. That view has dramatically changed in the past few decades, however, and transposable elements are now suspected by many scientists of having major roles in evolution, structure and function.
"Most plants have very large genomes because they contain huge amounts of transposable elements," said Dr. Susan Wessler, a professor of botany and genetics at UGA and principal investigator on the new NSF grant. "We believe that understanding how these elements function in rice will give us a new perspective on their role in evolution."
Co-principal investigators on the five-year project are Dr. John McDonald, a geneticist from UGA; Dr. Susan McCouch from Cornell University; and Dr. Sean Eddy of the Washington University School of Medicine in St. Louis.
More than 3 billion people around the globe depend on rice as their major staple. Only recently, however, has a project such as the one led by Wessler been possible. Geneticists have been making progress understanding transposable elements for some years but more often in plants like maize, where they were originally discovered. The human genome is, in fact, made up of 40 percent transposable elements,
Considerable work has already been done in understanding the genome of rice. The Genomics Institute at Clemson University is, in fact, one of the world centers for sequencing and studying the rice genome. Transposable elements make up an estimated 30 percent of the plant's genome.
"What distinguishes transposable elements from the genetic complement of an organism, among other things, is an ability to transpose and amplify," said Wessler, who is a member of the prestigious National Academy of Science. "They shake up an otherwise conservative genome and, in this way, both threaten and enhance genomic potential."
Wessler and McDonald are among the top national experts on transposable elements.
Aside from its importance as a food crop, rice is a logical next step for scientists studying transposable elements. While its importance is far less in the United States than in Asia, the genome of rice is only a fraction of the size of wheat's, making it much easier to study.
The percentage of transposable elements in any genome varies widely. The genes of some plants consist of more than 90 percent transposable elements, while in others the percentage may be less than 20 percent. Overall, however, transposable elements are a huge part of most genomes.
"The question asked all the time is whether these elements really matter," said Wessler. "The answer is that we do believe they play a significant role in genetic function and diversity."
The team's first step will be to identify by computer methods all the transposable elements in the rice genome. They will then study the elements in Wessler's lab, developing them as molecular markers to see if any of them are biologically active and contribute to genome diversity. Researchers believe some are activated in response to environmental stress.
Transposable elements may provide a way to diversify the genome in response to environmental changes.
Rice, corn, barley, wheat and sorghum are all grasses, and each species has numerous varieties bred over the centuries by farmers and scientists. The mechanisms behind all this genetic diversity is poorly understood, however, and transposable elements may play a major role in many of the plants' differences, such as size.
"The genomes of the grasses are extremely diverse, due in large part to the activity of transposable elements," said Wessler. "What we need to know is whether this diversity has functional consequences. If successful, this project will go al long way toward answering that question."
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