Light cues induce transcriptional reprogramming and protective anticipation of environmental water loss in Pseudomonas syringae

The ecological significance of light perception in non-phototrophic bacteria remains largely elusive. In terrestrial environments, diurnal oscillations in light are often temporally coupled to other environmental changes, including increased temperature and evaporation. Here we report that light functions as an anticipatory cue that triggers protective adaptations to tolerate a future rapid loss of environmental water in leaf-associated Pseudomonas syringae pv. syringae (Pss) and other terrestrial pseudomonads. Global transcriptome analyses in Pss showed that light control occurs almost entirely through a bacteriophytochrome photoreceptor that senses red, far-red and blue wavelengths and influences 30% of the Pss genome. Bacteriophytochrome-mediated light control disproportionally upregulates water-stress adaptation functions and confers enhanced fitness when cells encounter light prior to water limitation. These data demonstrate that non-phototrophic bacteria can use light as a cue to mount an adaptive anticipatory response against a physiologically unrelated but ecologically coupled stress. Comparative gene expression profiling analysis of RNA-seq data for Pseudomonas syringae pv. syringae strain B278a and isogenic mutants following brief exposure to different light wavelengths