Plant Genome Offers Clues To Longevity -- Arabidopsis Can Survive The Loss Of An Enzyme That Prevents Aging

The newest finding is from work funded by the National Science Foundation (NSF) division of molecular and cellular biosciences. It follows the December 2000 completion of the Arabidopsis genome sequence, which was achieved by an international team whose U.S. component was led by NSF.

"Much of the plant genome is very similar to the human genome," said Dorothy Shippen, Texas A&M associate professor of biochemistry and biophysics. "Also, because we can do these wonderful genetic tricks in plants, we think that much of what we learn in the plant system will be ultimately translatable, and perhaps have significant impact, in human medicine."

The findings, by Shippen, colleagues Tom McKnight and Lawrence Griffing of Texas A&M's biology department, and Texas A&M postdoctoral fellow Karel Riha, are in the current issue of the journal Science.

Telomeres seal the ends of chromosomes in plants and animals much like the plastic tip on the end of a shoelace. Like the plastic tip that wears out allowing the lace to fray and become hard to use, so does the telomere break down in most cells in the human body over time. For about 10 years, scientists have been looking at telomeres in humans for connections to cancer and aging.

"The integrity of the shoelace is maintained in large part because of this plastic tip," Shippen said. "In the same way, the telomere provides the stability for the chromosomes through many divisions of the cell."

The team used Arabidopsis because its complete genome sequence lets scientists find and study genes of particular interest. To examine differences telomeres make in plants, they generated an Arabidopsis mutant without functional telomeres.

"The enzyme telomerase, which is required for maintaining these structures on the ends of chromosomes, has been eliminated from the plant," Shippen said. "Now we are following the consequences of not having telomeres, and we are finding some remarkable features in these plants."

One key difference between plants and animals, Shippen noted, is that plants continue to live for a long time despite the catastrophic events they endure without telomeres. "The plants are able to take considerable genomic abuse which is a remarkable finding and differentiates, in a fundamental way, plants from animals," she said.

In similar studies of animal systems, cells have not been able to tolerate what a plant cell can. "Mammals have to keep a stable genome more than plants," Riha said.

"In animals, there is a strictly regulated pattern of development, and there is no way of turning back," McKnight added. "But plants are always making new organs throughout their lives. Plants are more flexible." The plant model developed at Texas A&M should provide scientists with greater insights about how telomeres allow chromosomes to become stabilized.

"Telomeres are essential timekeepers for how many times a cell can divide," she explained. "There's a strong correlation between telomeres and the ability of cancer cells to divide. So, if we can understand what a cell sees in terms of telomere structure and function that allows it to decide if a telomere is functional or not in plants, we hope that will be translatable to understanding how cell division is controlled in humans," she said.