A protein called enhanced disease susceptibility 1 (EDS1) plays a central role in plants' ability to defend themselves from pathogens. But in the almost two decades since it was discovered, how EDS1 works at the molecular level has been a mystery. Solving the mystery will help scientists enhance disease resistance in crops.
Two papers published in the Dec. 9 issue of Science demonstrate how EDS1 activates different components of the plant immune system, "a compartmentalization of the immune response that is novel," according to John M. McDowell, professor of plant pathology, physiology, and weed science in the College of Agriculture and Life Sciences at Virginia Tech.
In the invited article, "Beleaguered Immunity," in the Perspectives section of the journal, McDowell describes the discoveries being presented. Saikat Bhattacharjee, research scientist in plant sciences at the University of Missouri, is first author on one article, and Katharina Heidrich, Ph.D. student in Professor Jane Parker's group at the Max-Planck-Institute for Plant Breeding Research, Cologne, Germany, is first author of the other article. The two teams worked separately on the mystery but coordinated the submission of their articles to Science since the papers complement each other. "They independently confirm key findings and each manuscript has unique aspects," said McDowell, who is familiar with the system being studied through his research on EDS1 and on pathogen effector proteins.
It has been thought that EDS1 works downstream of a plant's first line of defense against pathogens; that its job has been to relay signals from the front line. "These papers show that EDS1 interacts physically with surveillance proteins within the plant cell," he said. “Moreover, EDS1 appears to play a role in activating distinct immune responses from different compartments within the plant cell.”
The research also shows how the EDS1 protein is attacked by virulence proteins from the pathogen, called effector proteins. Using the model plant, Arabidopsis, and a model pathogen, Pseudomonas syringae, the researchers observed that P. syringae drills through the plant cell wall and secretes effector proteins that target EDS1. "Plants have evolved a molecular hub that includes guardian proteins for EDS1," said McDowell. "So when EDS1 is attacked, surveillance proteins spread the alarm and various immune responses are activated to isolate the infection.
"This new research provides important confirmation of predictions about how pathogens operate," he said.
"How signals are relayed from the surveillance proteins to activate antimicrobial responses remains a mystery, but this detailed understanding of how EDS1 interacts with surveillance proteins may help scientists design a protein to guard EDS1 against attacks and make crops more disease resistant."
Arabidopsis is studied because it has a small genome and is easily manipulated, but EDS1 is present in almost all plants, McDowell said. "Almost everything we've learned from Arabidopsis we have been able to apply to crops." P. syringae is the model pathogen because it causes disease in many plants.