Lon Protease Is Important for Growth under Stressful Conditions and Pathogenicity of the Phytopathogen, Bacterium Dickeya solani

Abstract

The Lon protein is a protease implicated in the virulence of many pathogenic bacteria, including some plant pathogens. However, little is known about the role of Lon in bacteria from genus <i>Dickeya</i>. This group of bacteria includes important potato pathogens, with the most aggressive species, <i>D. solani</i>. To determine the importance of Lon for pathogenicity and response to stress conditions of bacteria, we constructed a <i>D. solani Δlon</i> strain. The mutant bacteria showed increased sensitivity to certain stress conditions, in particular osmotic and high-temperature stresses. Furthermore, qPCR analysis showed an increased expression of the <i>lon</i> gene in <i>D. solani</i> under these conditions. The deletion of the <i>lon</i> gene resulted in decreased motility, lower activity of secreted pectinolytic enzymes and finally delayed onset of blackleg symptoms in the potato plants. In the <i>Δlon</i> cells, the altered levels of several proteins, including virulence factors and proteins associated with virulence, were detected by means of Sequential Window Acquisition of All Theoretical Mass Spectra (SWATH-MS) analysis. These included components of the type III secretion system and proteins involved in bacterial motility. Our results indicate that Lon protease is important for <i>D. solani</i> to withstand stressful conditions and effectively invade the potato plant.