Ithaca, New York
May 15, 2003
The gene for an enzyme that is
key to natural disease resistance in plants has been discovered
by biologists at the Boyce
Thompson Institute for Plant Research (BTI) and at
Cornell University. The
researchers say that by enhancing the activity of the enzyme
they might be able to boost natural disease resistance in crop
plants without resorting to pesticides or the introduction of
non-plant genes.
The research, reported in the latest (May 16) issue of the
journal Cell, describes the discovery of the gene that codes for
an enzyme (a protein that carries out a chemical reaction) that
is activated when
a plant senses it is being attacked by a pathogen. When
activated, the enzyme produces nitric oxide (NO), a hormone that
tells the plant to turn on its defense arsenal.
According to plant pathologist Daniel F. Klessig, lead author of
the Cell paper and president of BTI, located on the Cornell
campus, the discovery provides a new understanding of the
biochemical and genetic pathways in plants that enable them to
protect themselves from disease.
"It's known that the hormone nitric oxide plays an important
role in immunity in plants as well as in humans and other
animals," says Klessig. "But the enzyme responsible for its
production in plants was unknown until now. With this discovery,
we may be able to modify plants so that they produce nitric
oxide more quickly, or in larger amounts, when they are attacked
by a disease-causing pathogen, enabling them to better protect
themselves from invaders."
Authors of the Cell paper, "The Pathogen-Inducible Nitric Oxide
Synthase (iNOS) in Plants is a Variant of the P Protein of the
Glycine Decarboxylase Complex," also include Meena Chandok, a
BTI senior research associate; Anders Jimmy Ytterberg, Cornell
doctoral candidate in plant biology; and Klaas J. van Wijk,
Cornell assistant professor of plant biology.
"This discovery really is a surprise because the plant enzyme
looks very different from mammalian nitric oxide-synthesizing
enzymes,"said Brian Crane, Cornell assistant professor of
chemistry and chemical biology. Crane now is working with
Klessig and Chandok to determine the three-dimensional structure
of the protein that will lead biologists to understand its
chemical mechanism.
The discovery is significant, the researchers note, because NO
is a critical early-warning signal to the plant that it needs to
activate its immune response. The difficulty inherent in the
research, according to Klessig, was that the plant's
NO-producing enzyme has a completely different sequence than
enzymes with similar activity found in all animals. The new
research suggests, he says, that the
chemistry the plant and animal enzymes use to produce NO also is
different.
These differences, Klessig says, could provide clues concerning
the way the animal enzyme works, which, in turn, could lead to
improved treatment of human diseases by enhancing the activity
of the enzyme.
"Part of the success of the green revolution depends on the use
of chemical-based fungicides and other pesticides to protect
crops against microbial pathogens and insects," says Klessig.
"An
alternative strategy to protect crops utilizes a plant's own
natural defenses. An approach in which plant molecular
biologists have overproduced plant proteins with antimicrobial
activity, such as PR
proteins or defensin, has met with only limited success to date,
perhaps because only a small portion of the defense arsenal is
involved.
"Our discovery of the enzyme that produces the critical
early-defense signal, NO, means that we now may be able to
regulate the production of this signal.
The turning up of this signal should lead to the turning on of a
large portion of the defense arsenal. The end result could be
crop plants that can better ward off disease without the use of
potentially harmful fungicides and other pesticides, or the
introduction of non-plant genes."
Van Wijk, whose research group identified the protein by tandem
mass spectrometry, stresses that without the availability of the
very sensitive mass spectrometry instruments and the plant
genome
information "we would not have been able to find this."
The Boyce Thompson Institute was opened in 1924 and is an
independent, not-for-profit plant research organization. BTI
funding for the Cell research was provided, in part, by a Plants
and Human Health Grant from the Triad Foundation.
Related World Wide Web sites: The following sites provide
additional information on this news release. Some might not be
part of the Cornell University community, and Cornell has no
control over their content or availability.
BTI: <http://bti.cornell.edu>
Cell: <http://www.cell.com>
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