Corn Smut Packs Health Benefits

PALO ALTO, Calif.Corn smut, a fungus that infects maize, can target its attack by choosing which of its genes to activate in order to maximize the effectiveness of its onslaught. This is the first time tissue-specific targeting has been found in a pathogen, according to new research from Stanford University. The finding upends conventional notions of how pathogens attack and could point the way to new approaches to fighting disease not only in plants but also in people.

"This establishes a new principle in plant pathology, that a pathogen can tailor its attack to specifically exploit the tissue or organ properties where it is growing," said Virginia Walbot, professor of biology and senior author of a paper published in Science. "It would be as if a pathogen of a human could recognize whether it is in muscle or kidney or skin, and activate different genes to exploit the host more effectively."

The researchers found that only about 30 percent of the genes in the corn smut genome are always activated, or "expressed," regardless of whether it is in seedlings, adult leaves or the tassel. The other 70 percent of the genome is what the fungus would pick and choose from, depending on the tissue it was infecting. Some of those genes were expressed in only one of the three organs the researchers studied; the others were activated in two of the three. The team also discovered that different parts of the maize plant activated different genes in response to being attacked.

We hope that other people working on pathogens of all types will go back now and ask, 'when the pathogen is found in different parts of the body, is it actually using different weapons?'" Walbot said. "We think this discovery will stimulate many new experiments with existing pathogens."

Corn smut, though a common pathogen, does not devastate maize crops and so relatively little work had been done by plant pathology researchers to study it. In Mexico, the fungus is called "huitlacoche," and the tumors, which are used in cooking, are sometimes purposely grown on ears of corn.

"If you order a mushroom omelet in Mexico, the fungus that you are eating is Ustilago maydis, or corn smut," Walbot said.

Though the new findings may not have much impact on those who savor corn smut for its culinary delights, researchers are likely to take note. "That is just a prediction, but I think pathologists will be quick to pounce on this," she said.