COLLEGE STATION — Researchers at Texas A&M and in New York have found a key to protecting plants from rice blast, the major disease affecting rice worldwide.
“This work represents a new approach to fighting rice blast,” said Dr. Daniel Ebbole, assistant professor of plant pathology and microbiology at Texas A&M University and a researcher with the Texas Agricultural Experiment Station. “Crop losses from the pathogen were estimated at 11 to 30 percent worldwide between 1975 and 1990. It’s the most important disease of rice.”
The researchers have confirmed that a specific yeast pheromone can keep the fungus Magnaporthe grisea from infecting rice. It does that by inhibiting production of a specialized cell in the fungus — called an appressorium — which allows M. grisea to penetrate host plant cells.
They must now find the best way to apply the knowledge but are optimistic that it will provide a useful tool in the fight against rice blast.
The findings were reported Thursday in the weekly journal Science. Ebbole, Texas A&M graduate student Janna Beckerman, and Dr. Fred Naider of the College of Staten Island’s department of chemistry authored the article.
The group was building on previous research by examining expression of an M. grisea gene needed for the formation of the appressorium.
They found that yeast extract inhibited appressorium formation in newly germinated spores of M. grisea. The response was specific to the mating type of the fungus, and this finding led them to believe it was a reaction to a pheromone-like substance that kept the appressorium from forming.
The fungus has two mating types, each necessary for the fungus to reproduce sexually. Known as MAT1-1 and MAT1-2 mating types, they are roughly analogous to gender in humans, with one of each type necessary for the fungus to reproduce sexually. Each mating type produces its own specific pheromone, a chemical that helps attract the other.
The researchers then experimented with the yeast pheromone, called alpha-factor pheromone, on M. grisea. Yeast is one of the best understood of all simple organisms and is a fungus, Beckerman said, which helped the researchers decide that a yeast pheromone might affect appressorium formation in the rice blast fungus.
“It was a guess, but it was a very good guess. It was a biorational approach,” said Beckerman, the paper’s lead author, who will receive her doctorate in plant pathology and microbiology in August.
The researchers confirmed that when synthetically produced alpha- factor pheromone stimulates the MAT1-2 strains, the M. grisea fungus does not develop appressoria.
Ebbole’s lab has also partially purified the pheromone factor produced by MAT1-1 strains of M. grisea that is recognized by MAT1-2 strains of the fungus and blocks appressorium formation.
“It’s using sex as a benevolent weapon, at least for us. It’s not so benevolent for the fungus,” Beckerman said.
Beckerman will be a post-doctoral researcher at the University of Minnesota following graduation. Ebbole’s laboratory, meanwhile, will continue working with strains of M. grisea that are common in the field, because the research they did was with laboratory-bred strains that are easier to work with.
They’ll collaborate with Dr. Marco A. Marchetti, a U.S. Department of Agriculture plant pathologist who works at the experiment station in Beaumont, on research involving field strains of the fungus.
Ebbole’s lab also will work on isolating the fungus genes that produce the pheromones, and they will examine the genetics of the pheromone response.
The pheromone could be directly applied to rice but would be expensive to manufacture and degrades easily in the environment. The researchers will seek similar but simple, inexpensive chemical compounds that will allow direct applications in the field.
Another possibility would be using the pheromone in genetically engineered plants or to have the pheromone produced by bacteria naturally inhabiting the leaf surface, Ebbole said.
However, Beckerman said, a solution should be much easier to find now that pheromonal affect has been identified.
“Because it specifically affects the rice blast fungus and won’t affect other fungi, plants or animals, a pheromone-based approach will be environmentally benign,” Beckerman said.
Funding for the research was provided in part by grants from the National Institutes of Health and the Texas Higher Education Coordinating Board.
“This is a great example of how support for basic science research can lead to new and unexpected approaches for solving important problems,” Ebbole said.
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