East Lansing, Michigan
September 6, 2007
Evil forces thrive in an unstable
environment.
At least, that’s the picture being painted in the first waves of
data being reaped from the genome sequence of the fungal plant
pathogen, Fusarium graminearum. The sequencing has provided
scientists a road map to someday combat a fungus that infects
wheat and barley crops, rendering them unusable.
In the September 7 edition of the journal
Science, Frances Trail,
Michigan State University
associate professor of plant biology and of plant pathology, and
Jonathan Walton, professor in the MSU-Department of Energy (DOE)
Plant Research Laboratory, joined scientists around the world in
picking over the inner workings of the fungus. The discovery:
The real estate in some parts of the chromosomes, where many
switches of disease and toxins reside, is unstable. Other areas
of the chromosomes, where basic metabolism and other vital
functions dwell, are stable.
“Those unstable areas are places where the organism is ready to
evolve,” Trail said. “In those genes there’s a lot of mutation.
They can change a lot without killing the fungus. The genes that
are involved in basic metabolism can’t change without killing
the fungus.
“We’re starting to see this kind of a pattern as genomes have
been looked at. It tells us something about what makes a
pathogen a pathogen.”
Understanding the layout of the genome is a high-stakes
proposition. This fungus is a serious pathogen of wheat and
barley in Michigan and throughout the Midwest. It causes
Fusarium head blight, which reduces grain yields, and taints
grain with mycotoxins that have been found to be detrimental to
human and animal health.
Fusarium begins its blighting ways as pinprick-sized pods that
spit spores into the air. The spores float over grain fields,
landing on flowering wheat and barley. The spores colonize the
wheat flowers. The often cool, wet weather of the Midwest
provides an ideal environment for the fungus to take hold.
The result: fields of blight, identified by withered, bleached
heads of grain. At harvest, many of the grains are shrunken and
white, and harbor the mycotoxins.
The fungal plant pathogen has some 14,000 genes sequenced. Trail
said the roles of some of them are understood, including which
ones help form the spores or help produce toxins. Trail’s team
figures that there are 2,000 genes dedicated to making the
spores.
“Those spores have to get out to cause the new disease cycle,”
she said. “If we can figure out that whole mechanism, it’s
likely that we can figure out a way to control it.”
Understanding the sequence is the first step in the process.
From there, the task is understanding the makeup of the genes –
where they’re strong and organized, where they’re unstable and
ready to change strategy. For instance, Trail wonders if that
flexibility in the pathogenic-holding parts of the chromosome is
the reason this fungus can produce so many different mycotoxins
– including zearalenone, which can mimic sex hormones in
mammals, including possibly people, and potentially cause
developmental and reproductive problems.
The research was funded by a joint program between the U.S.
Department of Agriculture, the National Science Foundation and
the DOE as well as supported by the Michigan Agricultural
Experiment Station. The sequencing was performed at the Broad
Institute at MIT.
Walton’s lab helped annotate the completed genome – that is,
inspect a subset of the 14,000 gene sequences for accuracy and
then compare them to genes in other organisms. In this way, they
identified genes that Fusarium has that are lacking in related
fungi that aren’t pathogenic on plants.
“This gives us additional clues as to what Fusarium needs to be
a pathogen, which we hope will lead to new strategies to control
the disease”. |
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