"When we started looking more closely, and put bacteria on a plant surface, stomata close. It's like they say 'oh, we have to close the doors!'" Melotto said. "Even if it is in bright daylight, when the stomata are supposed to be open, they close."
Some bacteria have gotten smarter. Melotto and Underwood found that plants recognized human-infecting bacteria, such as E. coli, and kept the stomata closed to them. Plant-infecting bacteria, like those most destructive to crops, have figured out a way to reopen the shut-down ports.
It appears those plant-based bacteria produce a phytotoxin, a chemical called coronatine, to force the pores back open. For bacteria, entry is crucial to causing disease and probably survival. They could die if left lingering on the surface. Animal-based bacteria do not produce coronatine.
"Now that we know a key step in bacteria's attack, we have something we can learn to interfere with," Melotto said. "From this we can learn about disease resistance."
It's a weighty issue. Bacterial diseases can be catastrophic to crops. One disease, called fire blight, did $40 million in destruction to Michigan apple trees in 2000 alone and all but eliminated commercial pear crops in Michigan for that year.
He also sees useful human health implications. Understanding that animal pathogens, like dangerous E. coli, cannot easily gain access inside the plant helps scientists know how to best combat bacteria that cause foodborne illness. It is important to know, he explained, whether foodborne illnesses rest on the surface of an edible plant, or nestle inside, impervious to washing.
"We are thinking about the mysteries of plant pathologies, but these have broad implications," He said. "We haven't understood very well how plants and bacteria interact, but we're finally seeing the ligh
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Contact: Sheng Yang He
hes@msu.edu
517-353-9181
Michigan State University
7-Sep-2006