Contact Information Rod Wing, professor Department of Plant Sciences 520-626-9595 rwing@genome.arizona.edu Related Web site Rice Genome Sequencing Consortium

Scientists who are decoding chromosome 10 of the rice genome have discovered that it has 3,471 genes - twice as many as expected - and it is nearly identical to other grains, particularly sorghum and maize. This advance, reported in the June 6 issue of Science, will assist in improving a crop that has been cultivated for more than 9,000 years and consumed by more than half the world's population.

"The nice thing about rice is that it has a very compact genome," said Rod Wing, a professor of plant sciences at the University of Arizona in Tucson and director of the Arizona Genomics Institute.

"Rice has 12 chromosomes and is considered a model plant for research in cereals. By decoding the rice genome we'll understand the regulatory networks involved in disease tolerance, drought tolerance and other mechanisms that will help in the breeding of rice varieties that are higher yielding, more stress tolerant and more environmentally friendly," Wing said.

The project is led by Wing, C. Robin Buell of The Institute for Genomic Research (TIGR) in Rockville, Md., and W. Richard McCombie of Cold Spring Harbor Laboratory in New York. Funding for the project came from the U.S. Department of Agriculture, National Science Foundation (NSF), National Institutes of Health and the Department of Energy.

A portion of chromosome 10 was also sequenced by the Plant Genome Initiative at Rutgers University.

The researchers are part of a 10-nation consortium decoding the entire rice genome. Wing and his team were responsible for the entire sequence and analysis of chromosome 10 and a draft sequence of the "short arm" of chromosome 3.

The consortium published a draft sequence of the complete rice genome in Science last December that included a more conservative estimate of the number of genes in chromosome 10, the smallest in the genome.

Going from the draft to the finished version has been painstakingly precise and costly, said Buell, because the process requires considerable lab work by an extended team of research associates. There are no short cuts. The resulting view, however, is immensely clearer - "like looking at the cosmos through a regular telescope, and then looking at it through the Hubble telescope," he said.

The work demonstrates the value of pursuing the full rice sequence in detail, according to Judith Plesset, a program director in the NSF Directorate for Biological Sciences, which supported the project. "One of the lessons here is, 'Don't think you know everything simply because you've done the draft,'" she said.

Buell, Wing and their colleagues combed through molecular databases, comparing proteins in chromosome 10 with those in Arabadopsis, a model plant from the mustard family with a genome that has been completely sequenced and documented. The researchers found matches for about two-thirds of the proteins, enabling them to identify specific genes for enzyme production, binding of nucleic acids, cell growth and maintenance, cell communication, immunity, development and other functions.

On the chromosome's "short arm," however, the team found very little that matched Arabidopsis. Though much more detailed than the draft, this version is not completely finished and has seven gaps, representing about four percent of the total sequence.

"This is a result of the limitation of sequencing technology," Plesset said. "As new technologies become available, these gaps will be filled."

Thus far other members of the international consortium have completed the sequencing for rice chromosomes 1 and 4. A full sequence for chromosome 3 is expected to be announced by the end of 2004. Once the entire rice genome is sequenced, scientists say they can use it as a model for estimating gene order in the much larger genomes of maize, barley and wheat.

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