Embargoed until 5 p.m. EST
NSF PR 02-18 - March 21, 2002
Protein Plays Espionage Role in Bacterial Attack
Scientists for the first time have identified a protein
that plays a double agent role in the war between
plants and disease causing bacteria.
The plant protein, called RIN4, interacts with both
invading pathogen molecules, and with another protein
from within the plant cell itself, in the plant's
disease resistance strategy. The discovery adds important
new knowledge to how bacterial pathogens target a
host plant's molecular machinery to make it more hospitable,
even beneficial, to its plundering invasion.
"This research will increase our understanding of how
plant genes mediate resistance to pathogenic bacteria
that cause disease and crop losses," says Sharman
O'Neill, program director in the National Science
Foundation's (NSF) division of integrative biology
and neuroscience, which funded the research along
with the Department of Energy (DOE).
"This information is likely to lead to novel approaches
for pathogen control, and to improved disease resistance
in plants. The combination of genetics and biochemistry
will allow a unique assault on a disease resistance
signaling pathway," said O'Neill.
The research, done at the University of North Carolina
at Chapel Hill (UNC-CH), is reported in the March
22 issue of the journal Cell.
"This study is largely about how plants perceive pathogens,"
said senior study author Jeff Dangl of the UNC-CH
school of medicine. "When we study the interaction
between host and pathogen, we need to understand it
from the pathogen side, including the targets it wants
to hit and why, the weapons it uses, and -- on the
plant side -- what guard molecules the host deploys."
Dangl and colleagues studied how the wild mustard plant
Arabidopsis thaliana responds to Pseudomonas
syringae, a bacterial pathogen that also causes diseases
in crops like beans, peas and tomatoes. The mustard
plant has counterparts of many important human proteins
involved in disease, including cystic fibrosis and
The researchers focused on the Arabidopsis disease
resistance protein, RPM1, which they previously showed
was anchored to the inside of the plant cell membrane.
Until now, no one had found a direct interaction between
the pathogen's type III effector proteins and the
RPM1 receptor. The new study identified such a target,
the protein RIN4.
"RIN4 is a protein that bridges between the pathogen-encoded
type III disease effector and the plant-encoded disease
resistance protein," Dangl said.
When type III effectors are inside the cell, a phosphate
is added to RIN4. Dangl and colleagues postulate that
this reduces cellular defense. Thus, RIN4 "is normally
a negative regulator of defense, and the type III
effectors target it and lock it into a negative regulatory
mode. Pathogen growth would be facilitated by slowing
the host defense response," Dangl said.
But the resistance protein RPM1 appears to serve as
a "guard" for cellular proteins that are potential
targets of pathogen molecules, like RIN4.
Dangl and other researchers in this field believe that
resistance gene products such as RPM1 might be deployed
to physically associate with those targets and to
intercept the pathogen molecule when it enters the