Science Daily, Purdue University, Oct. 5, 2007 — Why a pathogen is a pathogen may be answered as
scientists study the recently mapped genetic makeup of a fungus that
spawns the worst cereal grains disease known and also can produce toxins
potentially fatal to people and livestock.
A fungus called Fusarium graminearum causes head blight, or scab,
which causes more damage to cereal grains than any other disease.
Purdue molecular biologist Jin-Rong Xu is using the fungus' genome to
find ways to prevent it. The laboratory dish on the left shows the
pathogenic fungus that attacks wheat, barley and some other small
grains. The right dish shows Fusarium graminearum that has been
genetically modified so that it won't cause the disease. (Credit:
Purdue Agricultural Communication photo/Tom Campbell)
The fungus, which is especially destructive to wheat and barley, has
resulted in an estimated $10 billion in damage to U.S. crops over the
past 10 years. The scientists who sequenced the fungus' genes said that
the genome will help them discover what makes this particular pathogen
so harmful, what triggers the process that spreads the fungus and why
various fungi attack specific plants.
These investigations also may lead to producing plants that are
completely resistant to the fungus Fusarium graminearum, something that
hasn't been possible previously, said Jin-Rong Xu, a Purdue University
molecular biologist. He is pinpointing which genes enable the fungus to
cause the disease Fusarium head blight, or scab.
In a recent issue of the journal Science, Xu and an international
scientific team reported that certain chromosomal regions in Fusarium
graminearum appear to dictate plant and fungus molecular interactions
that allow the fungus to contaminate crops and cause disease.
The researchers located all of the genes on the fungus' chromosomes
and then determined the genes' chemical makeup, or sequence.
"The Fusarium graminearum genome was easy to assemble because, unlike
other fungal genomes, there aren't too many repetitive DNA sequences,"
Xu said. "It seems that this Fusarium can efficiently detect and remove
duplicated sequences or transposable elements, which kept the genome
clean and well-organized."
This basic information on the Fusarium graminearum genome will aid in
further research and also provide information on other fungi and their
interaction with plants, he said.
"Because we now have the genome sequence and a microarray containing
the whole genome, it will help us determine what genes allow this fungus
to behave as it does," Xu said. "It also will make it easier to identify
and determine the function of similar genes in other pathogens and their
Fusarium graminearum, which exists worldwide, cuts crop yield,
damages grain quality and produces mycotoxins. The fungus caused a
widespread head blight epidemic during the 1990s in wheat- and
barley-growing regions around the world. Experts estimate that from 1998
to 2000 the central and northern Great Plains of the United States
suffered economic losses of $2.7 billion due to the disease. In Indiana
alone in 1996, the fungus caused at least $38 million in crop loss,
according to the USDA.
The mycotoxins caused by the fungus can affect people and livestock
that ingest infected grain. Pigs, cattle, horses, poultry and people can
develop vomiting, loss of appetite, diarrhea, staggering, skin
irritation and immunosuppression. The most severe cases can be fatal.
Some scientific evidence suggests that these toxins cause cancer.
People in developing countries are at the greatest risk of eating grain
contaminated with Fusarium mycotoxins. Although not all types of
Fusarium cause disease and produce toxins, those types that do infect
other crops, including corn and hay.
Currently, fungicides aren't effective because the fungus only
attacks during the beginning of the plants' flowering stage. It's
difficult to gauge the precise time to spray, and it's expensive to try
to protect the crops over a long period. The fungus can survive through
the winter in crop remnants left in fields as natural mulch.
The pathogen is most likely to appear and cause infection in early
spring when the weather is warm and humid or rainy. By the time Fusarium
contamination is noticeable on plants, head blight has already damaged
Xu is searching for the genes involved in the infection process.
"We are using the whole-genome microarray of Fusarium graminearum to
identify the genes that are functional during plant infection," Xu said.
"We are looking at the biochemical signaling pathways that influence
whether a gene is turned on or off. This will help us find ways to
develop new, stable and environmentally safe ways to prevent these
Xu was one of the co-applicants for a $1.9 million grant from a U.S.
Department of Agriculture/National Science Foundation partnership that
funded the genome project. The endeavor was headed by Corby Kistler, a
USDA-Agricultural Research Service geneticist based at the University of
Christina Cuomo of the Broad Institute at the Massachusetts Institute
of Technology led the sequencing. Other members of the research team
included scientists from Michigan State University; Cornell University;
Pacific Northwest National Laboratory; University of Arizona; St. Louis
University; University of Tennessee; and institutions in Germany,
Canada, Austria, England, France, Ukraine and the Netherlands.
Note: This story has been adapted from material provided by