Embargoed until 2:00 EST
NSF PR 01-15 - March 1, 2001
Tom Garritano, NSF
Joanne Tornow, NSF
Texas A&M University
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Plant Genome Offers Clues to Longevity
Arabidopsis can survive the loss of an enzyme that
Researchers studying the tips of chromosomes in Arabidopsis
thaliana-a weed in the mustard family-are learning
about gene functions that determine how rapidly plants
age, which could lead eventually to advances in human
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
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
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
"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,"