Embargoed until 2:00 P.M., EST
NSF PR 02-15 - February 27, 2002
Researchers Discover Mechanism of Plant Resistance
Plants have effective mechanisms aimed at protecting
themselves against bacteria and fungi. Research funded
by the National Science Foundation (NSF) and published
in the February 28 issue of Nature uncovers
the molecular basis by which this resistance occurs.
The work holds promise for designing hardier crops.
"We've identified a key molecular pathway within plant
cells," says scientist Jen Sheen of the molecular
biology department at Massachusetts General Hospital
(MGH), who authored the Nature paper with several
of her colleagues. "If we activate this pathway in
leaves, we've found that we can make them more resistant
to pathogens like bacteria and fungi."
Adds Jane Silverthorne, program director in NSF's biological
sciences directorate, "This is an exciting step forward.
For the first time, we have a detailed description
of an important plant signaling pathway. This information
will be valuable to furthering our understanding of
basic signaling mechanisms in plants, as well as for
developing crops with improved resistance to pathogens."
Sheen says plants have an effective and sophisticated
immune system. Their first line of defense is a thick
cell wall covered with cuticle layers that acts somewhat
like human skin. If a pathogen is able to penetrate
this physical barrier, for example through a wound,
the pathogen will usually be detected by receptors
on the surface or inside of the plant cells. One of
the best characterized pathogen receptors has a feature
characteristic of other plant receptors known as a
Leucine-rich repeat (LRR) receptor kinase. This receptor
kinase can recognize a structure on bacterial pathogens
called flagellin that makes the bacteria motile.
"There's a conserved region in the flagellin that's
present on a wide range of bacterial pathogens, so
plants are very effective at detecting pathogens.
Highlighting the conservation and similarity of immune
systems in plants and animals, bacterial flagellin
can also trigger innate immune response through a
LRR receptor in mammals," explains Sheen.
When the plant receptor binds flagellin, a complex
set of cellular events follow, resulting in the expression
of key immune response genes.
"The receptor in plant cells is connected to a signaling
cascade that activates gene expression through what's
known as transcription factors," Sheen says. In particular,
these transcription factors may trigger the production
of certain plant signals, reminiscent of cytokines
in mammals, that then turn on a lot more downstream
genes directly involved in the defense mechanism of
the plant, Sheen explains.
The whole process is a complicated cascade of events
that Sheen and her colleagues are continuing to unravel.
"We are currently investigating the downstream genes
involved in this cascade. Ultimately, it looks like
the end result is that the plant is able to produce
a variety of anti-microbial proteins, enzymes and
chemicals." Sheen adds that the ultimate goal of this
type of research is to be able to engineer plants
to become more pathogen-resistant.
The study was also supported by the U.S. Department
of Agriculture, the National Institutes of Health,
the Toyobo Biotechnology Foundation, and the Uehara
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