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 Dickeya. This group of bacteria includes important potato pathogens, with the most aggressive species, D. solani. To determine the importance of Lon for pathogenicity and response to stress conditions of bacteria, we constructed a D. solani Δlon 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 lon gene in D. solani under these conditions. The deletion of the lon gene resulted in decreased motility, lower activity of secreted pectinolytic enzymes and finally delayed onset of blackleg symptoms in the potato plants. In the Δlon 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 D. solani to withstand stressful conditions and effectively invade the potato plant.
Highlights
Bacteria from the genus Dickeya, together with Pectobacterium, are classified as soft rot Pectobacteriaceae (SRP) [1]
A lon deletion mutant of D. solani was constructed using the gene doctoring method, a modified protocol for lambda red recombination dedicated to the pathogenic bacterial strains
The gene encoding the Lon protease was substituted with the kanamycin resistance cassette, amplified from the pDOC-K plasmid
Summary
Bacteria from the genus Dickeya, together with Pectobacterium, are classified as soft rot Pectobacteriaceae (SRP) [1]. The virulence factors that are primarily involved in the development of the disease symptoms caused by D. solani are plant cell wall degrading enzymes (PCWDE). This group of proteins encompasses pectinases, cellulases and proteases, whose joint action leads to maceration of plant tissues. An effective infection process requires an array of other virulence determinants These include the ability to actively move (motility) toward wounded tissue (chemotaxis), production of antioxidants, siderophores, secreted effectors and, cellular factors that provide survival under unfavorable environmental conditions inside the host plant. The effectors frequently manipulate host signaling pathways to disable the plant’s defense systems to enable successful infection (reviewed in [8])
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