Fungus Genome Yielding Answers to Protect Grains, People, and Animals

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Fungus Genome Yielding Answers To Protect Grains, People And Animals

Science Daily — 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 )

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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 plant interactions. "

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 the grain.

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 infections. "

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 Minnesota.

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.