University of Purdue Sequencing Genes for Dangerous Fungus

At Purdue University, Jin-Rong Xu, a Purdue University molecular biologist, is searching for the genes involved in the infection process relevant to the fungus Fusarium graminearum, which spawns the worst cereal grains disease known and can also produce toxins potentially fatal to livestock and people.

Wheat and barley in particular are destroyed by the graminearum fungus. Infection in U. S. crops over the last ten years has resulted in an estimated $10 billion in damages. Scientists have sequenced the fungus' genes and are studying the mapped genetic make-up in the hope that it 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.

Sequencing occurs after researchers located all the genes on the fungus' chromosomes and then determine the genes' chemical make-up.

"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."

"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."

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 Fusarium graminearum fungus exists worldwide. It cuts crop yield and damages grain quality. In addition it produces mycotoxins that can be dangerous or even fatal.

The mycotoxins produced by the fungus affect livestock and people when fungus-infected grains are ingested. Among livestock, pigs cattle, horses and poultry can develop severe to fatal cases of disease. People who ingest the infected grains suffer the same symptoms as do the livestock and likewise develop severe to fatal cases of illness. symptoms are loss of appetite, staggering, skin irritation, vomiting, diarrhea, and immunosuppression. The most severe cases can be fatal.

People in developing countries are at the greatest risk of inadvertently eating grain contaminated with Fusarium mycotoxins. Some scientific evidence suggests that these mycotoxins may cause cancer.

During the 1990s the fungus caused a worldwide epidemic in wheat- and barley-growing regions. In the U. S. alone there was an economic loss in the Great Plains of $2.7 billion dollars.

Fungicides currently aren't effective because the fungus only attacks during the beginning of the plants' flowering stage, making a precise time for spraying hard to gauge. Additionally, the fungus can survive through the winter in crop remnants that have been left in fields as natural mulch.

Early spring is the time the pathogenic mycotoxin is most like to appear and cause infection since this is a time when the weather is rainy or warm and humid and early plants are in the early flowering stage.

"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."

The issue of genetic modification of plants is one of international and local contention and concern. Yet it must be noted that these investigations may also lead to producing plants that are completely resistant to the fungus Fusarium graminearum, according to Xu. He is pinpointing which genes enable the fungus to cause the disease precipitated by Fusarium graminearum.

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.

Susan A. Steeves, "Fungus genome yielding answers to protect grains, people and animals," Purdue University.