Cyanidin Is a Host Signal for Pseudomonas Syringas to Regulate Virulence and Biofilm

Pseudomonas syringae is a widespread plant pathogen, causing huge economic losses and presenting a threat to food security worldwide. Like many other Gram-negative pathogens, P. syringae uses its type III secretion system (T3SS) to invade host plants and cause lethal diseases. Although a number of components have been identified to regulate T3SS, how the bacterium senses host signal(s) and further transduces the signal(s) to the known regulatory factors remain largely unknown. We have recently identified a novel host signal, cyanidin, which directly binds and activates the two-component system RhpRS and thus inhibits T3SS as well as biofilm of P. syringae. Pro40 in the Nterminal sensor domain and Pro89 in the HAMP domain of RhpS play essential roles in cyanidin perception. Based on these preliminary results, we propose a novel signaling pathway of cyanidin-RhpRS-T3SS/biofilm, whose verification is the focus of the proposal. Genetic and biochemical characterizations of this novel signaling pathway is the first step toward identifying signals to which the T3SS responds, and toward the development of new strategies for disease control based on T3SS manipulation. Our long-term goal is to leverage the outcomes of the herein proposed studies to develop better therapies against P. syringae infection.