Pseudomonas syringae pv. tomato exploits light signals to optimize virulence and colonization of leaves

Bacterial pathogens that inhabit the phyllosphere are exposed to light during their life cycle. Light enhances plant defenses and regulates opening of stomata, an entry point for foliar bacterial pathogens such as Pseudomonas syringae pv. tomato DC3000 (PsPto). However, the extent to which pathogens exploit light signals to promote virulence and plant infection is poorly understood.

Researchers of the CBGP (UPM-INIA) belonging to the group “Phytopathogenic Bacteria” have revealed that light perception induced genetic reprogramming in PsPto that entailed significant changes in stress tolerance and virulence-related traits. The effects of the presence, absence and quality of light on gene expression, together with the physiological stage of the plants with respect to the diurnal cycle at the time of inoculation determine the virulence output. In addition, this work presents evidence for nocturnal priming, a phenomenon in which PsPto cells express selected virulence traits prior to dawn when light is absent, and this expression contributes to virulence by optimizing entry into leaves through the stomata following dawn. Thus, just as plants exploit light cues to maximize their resistance to pathogens, bacteria can exploit light cues to maximize their virulence on plants.