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Columns::April 21, 2003
Honors and Awards
UGA’s top students and teachers recognized at Honors Day ceremony
University hosts state championship for future problem solvers
The greening of South Campus
Office of Research Services appoints a new director
Education dean receives diversity award from housing residents
On-the-job training: Engineers team up with businesses for new designs
Lifelong interest in animals leads prof to career as wildlife biologist
Retirees
Kudos
Forum essay: International education
Making a scene
Across the board
Campus News
Flower(ing) power
UGA scientists plot key events in plant evolution
By Cat Holmes
clholmes@uga.edu
Since Charles Darwin grasped evolution more than 150 years ago, scientists have sought to better understand when and how the
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Arabidopsis
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vast variety of plants today diverged from common ancestors.
A new UGA study, just published in Nature, demonstrates key events in plant evolution. It allows scientists to infer what gene order may have looked like in a common ancestor of higher plants. And it shows one way plants may have differentiated from their ancestors and each other.
“By studying the completed sequence of the smallest flowering plant, Arabidopsis, we showed that most of its genes were duplicated about 200 million years ago and duplicated again about 80 million years ago,” says Andrew Paterson, the plant geneticist who directed the study. “The ensuing loss of ‘extra genes’ caused many of the differences among modern plants.”
Two years ago, scientists finished the genetic sequencing of Arabidopsis, a small, weedy plant. It was a major event--the first plant to be completely sequenced. Arabidopsis had been chosen on the assumption that it would be fairly easy, since it was small. Sometimes small packages aren’t so simple.
Seeded throughout its five chromosomes were thousands of genes that seemed to be “junk.” When UGA scientists compared all of the genes, they found evidence of duplicated “blocks” of similar sets of genes in two, four or eight different places along the chromosomes.
It’s well-known that many plants contain two or more copies of most genes. But why these copies exist and when they occurred has been unknown. Their surprising abundance in the tiny, well-studied Arabidopsis indicated that genome duplications may have played a bigger evolutionary role than was previously thought.
Why were these blocks of genes duplicated? When did it happen? Answering these questions involved a lot of computerized comparing and contrasting.
The scientists repeatedly compared related pairs of Arabidopsis genes with genes from other plants to figure out which genes had been “hanging out with each other,” says UGA graduate student Brad Chapman, who co-authored the study with John Bowers, Junkang Rong and Paterson. “Genomes with similar blocks of duplication, ‘spelled’ in similar ways, had been hanging out together for longer periods of time.”
“We tested many, many combinations,” Paterson says. “We tested Arabidopsis with cotton, cauliflower, alfalfa, soybeans, tomatoes, rice, pine trees and moss.”
After more than 22,000 such comparisons, the results were pooled, and the scientists looked for breakpoints. The breakpoints indicated duplication events, says Paterson. And the result indicates that Arabidopsis has duplicated at least twice, and perhaps a third time.
Each time a duplication event occurred, the entire genetic sequence of Arabidopsis doubled. The plant lived on with spare copies o
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Andrew Paterson
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f all of its genetic material. And over time, the “extra genes” were shuffled around or lost. This may be one explanation for how different species emerged.
“The duplication event that occurred 200 million years ago occurred in virtually all plants,” Paterson says. “The duplication event 80 million years ago affected a lot of plants, but not as many.”
The study is attracting attention in the scientific community because it combines an evolutionary approach with genomic data to learn more about the natural world.
This information will have a significant economic impact because it permits scientists to make better use of the Arabidopsis sequence.
It will also allow them to study and improve other plants whose DNA hasn’t yet been completely sequenced, such as peanuts, cotton or wheat, saving both time and money.
“For example, we can take the 2,000 genes known on the cotton map, compare them with the Arabidopsis sequence and, with this analysis, make good, educated guesses about where the other 48,000 cotton genes are,” Paterson says. |
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