While rice feeds half the world, its relatively simple genome helps scientists understand the genetics of other plants. According to the Science report, "Rice is considered a model system for plant biology largely due to its compact genome (430 million base pairs, or Mb, on its 12 chromosomes) and evolutionary relationships with other large-genome cereals, such as sorghum (750 Mb), maize (2,500 Mb), barley (5,000 Mb) and wheat (15,000 Mb)."

Added NSF's Plesset, "We can use rice as a reference for understanding the organization, structure and function of much larger genomes such as maize and wheat. Scientists can use a rice gene to find its counterpart in any of the cereal genomes."

Seeking to identify the roles of the chromosome's genes by combing through molecular databases, Buell, Wing and their colleagues compared chromosome 10's proteins with those of another model plant, Arabidopsis, a member of the mustard family whose genome has been completely sequenced and extensively documented. Matches were found for about two-thirds of the proteins, indicating some of the specific genes responsible for enzyme production, binding of nucleic acids, cell growth and maintenance, cell communication, immunity, development and other functions and processes.

On the chromosome's "short arm," however, they found very little that matched Arabidopsis. Instead, there they found an abundance of heterochromatin, a stretch of highly compacted DNA with few genes among it, a chromosomal substance for which the biological function is unknown.

Though much more detailed than the draft, this version is not completely finished and has seven gaps, representing about 4 percent of the total sequence.

"This," Plesset said, "is a result of the limitation of sequencing technology. As new technologies become av
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Contact: Sean Kearns
skearns@nsf.gov
703-292-7963
National Science Foundation
5-Jun-2003