"Footprint" Shows Master Switch Simultaneously Controls Plants' Disease Defenses

"Because their core sets of genes are so similar, a genetic 'footprint' like the one we found could be a binding site for a universal switch for the immune system among many plant species," said Dr. Jeffery L. Dangl, John N. Couch associate professor of biology at UNC-CH. "This discovery, on this scale, is a first for plant biology."

Working with Arabidopsis, a member of the mustard family widely considered the "laboratory mouse" of the plant kingdom, the scientists analyzed expression of about 8,000 plant genes and tested them under 14 different conditions that either turned on or turned off the plant's immune system. New genomics technology enabled them for the first time to simultaneously test the large group of genes, which are a third of the total number of genes in Arabidopsis.

"We found a small group of about 30 genes that all behaved the same way under the different treatments we subjected them to," Dangl said. "That meant that they were responding to something in common. We found that each gene in this group has one short sequence of DNA, in essence a footprint, in a position called the promoter, which controls when the genes are turned on and off. "

A report on the discovery appears in the Dec. 1 issue of Nature Genetics, a major scientific journal. Besides Dangl, other UNC-CH authors are former undergraduate Aaron Levine and postdoctoral fellow Dr. Thomas Eulgem. Syngenta authors are Drs. Klaus Maleck, Allen Morgan, Jurg Schmid, Kay Lawton and Robert A. Dietrich, a former postdoctoral fellow at UNC-CH.

Among the 30-gene group, the researchers found, are 10 to 15 previously unknown genes that probably play important but undefined roles in protecting plants against disease.

"Now we can use the footprint to find the controlling switch and eventually engineer it to create a plant that would respond better or more quickly to attack by disease-causing organisms such as bacteria and fungi," Dangl said. "This could be very important for food production and plant health in general."

Scientists study Arabidopsis because it's small and can produce five to six generations a year rather than just one or two like traditional crop plants, the biologist said. That rapid reproduction allows them to study the plant's genetics faster than they could with other species.

Understanding Arabidopsis completely will teach scientists an enormous amount about all other flowering plants, which are closely related genetically. The new genomics technology, developed by Patrick Brown and David Botstein at Stanford University, has been applied to yeast, fruit flies and humans but not to plants in a large, systematic way, he said.

"This is a classic example of a tight, open collaboration between the university and private industry and highlights the value of including undergraduates in research on campus," Dangl said. "Among its contributions, Syngenta gave us access to technology we needed but did not have on campus at the time, and that collaboration has paid off."

"Our research project has yielded some very novel information that already is proving helpful to other scientists around the world," he said. "All our raw data will be available publicly over our Web site for anyone to use and to help them make further discoveries."