The scientists found that both of these effector molecules effectively shut down the PAMP pathway. But the plant's R-proteins detect this, and come to the rescue.
"The R-proteins detect the insidious activity by which the pathogen's effectors block the PAMP pathway," Mackey said. "PAMP defense responses are probably often effective, but they may be blocked by the pathogen's effector proteins. If an R-protein recognizes a pathogen's presence, it usually induces a very strong immune response, in most cases stopping a would-be infection.
"This work further suggests that plants use an active, complex immune system to combat pathogens," he said. "They have complicated surveillance systems that detect various infection-causing molecules and trigger defensive responses."
A next step in this line of work is to look at other pathogen effector proteins and analyze their role in causing infections.
Mackey conducted the study with Ohio State colleagues Min Gab Kim, a graduate student in the department of plant cellular and molecular biology, and graduate student Luis da Cunha and post-doctoral fellow Aidan McFall, both in the department of horticulture and crop science; Youssef Belkhadir and Jeffrey Dangl, both with the department of biology at the University of North Carolina, Chapel Hill; and Sruti DebRoy, formerly of the U.S. Department of Energy Plant Research Laboratory at Michigan State University.