Oxygen-sensing hydroxyproline regulates Pseudomonas syringae virulence

Pseudomonas syringae is a globally important gram-negative plant pathogen. P. syringae uses its type III secretion system (T3SS) to drive host invasion and disease. However, how host-derived signals are sensed and are routed to T3SS regulators remains unclear. Building on extensive work defining RhpRS as a central switch, we have recently revealed a novel hydroxyproline (hyp) modification at Pro89 in the RhpS HAMP domain, which is elevated in minimal medium but suppressed by hypoxia. We hypothesise that a conserved prolyl hydroxylase (ProH) catalyzes this modification to repress rhpR and activate T3SS and motility gene expression, while limiting biofilm expression. Based on these preliminary results, we propose a novel signaling pathway of ProH–Hyp–RhpRS–virulence, 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.