Embargoed Until 4 P.M., EST
NSF PR 96-88 - December 19, 1996
This material is available primarily for archival purposes. Telephone
numbers or other contact information may be out of date; please see current
contact information at media
contacts.
Disease Resistance Mechanism Identified in Plants
A molecular mechanism for plant disease resistance
has been identified for the first time by researchers
funded by the National Science Foundation (NSF).
Studying "bacterial speck disease" in tomatoes as
a model, the researchers confirmed a decades-old notion
that disease resistance in plants is triggered by
the interaction of proteins produced by both a resistance
gene in the plant and an "avirulence" gene in the
disease-causing microorganism. The avirulence protein
acts much like an antigen in animals, eliciting an
immune response from the plant. Researchers suspect
that the resistance mechanism observed in tomatoes
also occurs in many other plants. Their results appear
in the December 20 issue of the journal Science.
Having identified this basic gene-for-gene resistance
mechanism, researchers plan to further explore the
phenomenon. Biologist Greg Martin of Purdue University
in Indiana says the findings will have wide application.
"It turns out that plants resist diverse pathogens
-- including bacteria, fungi and viruses -- by using
very similar defense mechanisms. By understanding
how a plant recognizes one pathogen, we should begin
to understand how plants identify many different pathogens,"
Martin said.
"This is the first demonstration that there is a lock-and-key
mechanism at the molecular level involved with the
plant's ability to recognize and mount a resistance
response to a pathogen," adds Steven Scofield, a research
geneticist at the University of California at Davis
Center for Engineering Plants for Resistance Against
Pathogens, an NSF Science and Technology Center.
For some 40 years, researchers have known that a plant's
ability to fend off an attacking bacterial or viral
disease is somehow linked to the complementary activity
of genes in both the plant and the pathogen - the
disease-causing agent. Previous genetic research has
suggested that an avirulence gene in the pathogen
triggers a resistance response in the infected plant.
The researchers tested this conjecture using bacterial
speck disease, caused by a bacterium known as Pseudomonas
syringae pv. tomato (Pst). It is well known that
resistance to Pst is contained in the tomato's Pto
resistance gene, which has been bred into most commercial
tomato varieties. The researchers speculated that
the bacterial avirulence gene (AvrPto) enters the
plant cell by moving across the plant cell wall and
its inner lining, the plasma membrane. Once inside
the plant cell, it directly interacts with the tomato
plant's Pto resistance gene.
To test this, the researchers first inserted the avirulence
gene into a variety of tobacco plant that had been
genetically engineered to carry the tomato resistance
gene. The tobacco plant was used in this experiment
because it was easier to genetically manipulate than
a tomato plant. The result was a pattern of cell death
or necrosis known to result from the resistance gene,
suggesting that the products of the resistance and
the avirulence genes were interacting directly.
"These findings set the stage to allow us to genetically
engineer disease-resistant crops," Brian Staskawicz,
a biologist at UC-Berkeley concludes.
Editors: For a color photo of scientist Greg
Martin at work in his lab with a tomato plant call
Steve Tally, Purdue University at: (317) 494-9809.
|