Our primary interest is in understanding the genetic and biochemical basis of disease resistance in plants. Plants are able to specifically recognize pathogens and actively respond. We are investigating how this specific recognition is accomplished and how recognition is translated into a resistant response. To address these questions we take a molecular genetic approach. We use the small mustard Arabidopsis thaliana as our standard host plant, and the bacterial pathogen Pseudomonas syringae as our standard pathogen. Recognition of specific P. syringae strains by Arabidopsis is mediated by specific disease resistance (R) genes of Arabidopsis. These R genes are thought to encode receptors that detect a signal produced directly or indirectly by bacterial proteins that are injected into the plant cell. The molecular mechanism of this detection step is poorly understood, however. Understanding this mechanism is a major goal in plant biology as it will likely lead to new approaches for engineering disease resistance in plants, as well as provide critical insights into how pathogens evolve to escape recognition and cause disease. Our work is also providing new insights into the human immune system as humans use similar proteins to detect pathogens.