ABSTRACT: Lon protease plays vital roles in many biological processes in Pseudomonas syringae, including type III secretion systems (T3SS), transcription regulation, protein synthesis and energy metabolism. Lon also functions as a transcriptional regulator in other bacterial species (e.g., Escherichia coli and Brevibacillus thermoruber). Therefore, we hypothesise that Lon has dual functions in P. syringae. To reveal the molecular mechanisms of Lon as a transcriptional regulator and protease under different environmental conditions, we used a combination of transcriptome sequencing (RNA-seq), chromatin immunoprecipitation sequencing (ChIP-seq) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify the genes or proteins regulated by Lon. As a transcriptional regulator, Lon bound to the promoter regions of PSPPH_4788, gacA, fur, gntR, clpS, lon and glyA and consequently regulated 1-dodecanol oxidation activity, motility, pyoverdine production, gluconokinase activity, N-end rule pathway, lon expression and serine hydroxymethyltransferase (SHMT) activity in King’s B medium (KB). In minimal medium (MM), Lon regulated SHMT activity and lon expression by binding to the promoter regions of glyA and lon, respectively. As a protease, Lon regulated the T3SS and metabolic pathways (e.g., amino acid metabolism). In MM, Lon regulated the polysaccharide metabolic process by controlling PSPPH_0514, AlgA, CysD and PSPPH_4991. Taken together, these data demonstrate that Lon acts as a transcriptional regulator or protease in different environments and tunes its virulence and metabolic functions accordingly.
