Lack of RsmA-Mediated Control Results in Constant Hypervirulence, Cell Elongation, and Hyperflagellation in Pectobacterium wasabiae

Abstract

The posttranscriptional regulator RsmA controls the production of plant cell wall degrading enzymes (PCWDE) and cell motility in the Pectobacterium genus of plant pathogens. In this study the physiological role of gene regulation by RsmA is under investigation. Disruption of rsmA gene of the Pectobacterium wasabiae strain, SCC3193 resulted in 3-fold decrease in growth rate and increased virulence. The comparison of mRNA levels of the rsmA− mutant and wild-type using a genome-wide microarray showed, that genes responsible for successful infection, i.e. virulence factors, motility, butanediol fermentation, various secretion systems etc. were up-regulated in the rsmA− strain. The rsmA− strain exhibited a higher propensity to swarm and produce PCWDE compared to the wild-type strain. Virulence experiments in potato tubers demonstrated that in spite of its more efficient tissue maceration, the rsmA− strain's ability to survive within the host is reduced and the infection site is taken over by resident bacteria. Taken together, in the absence of RsmA, cells revert to a constitutively infective phenotype characterized by expression of virulence factors and swarming. We hypothesize that lack of control over these costly energetic processes results in decreased growth rate and fitness. In addition, our findings suggest a relationship between swarming and virulence in plant pathogens.

Regulation of Bacterial Virulence by Csr (Rsm) Systems

“…RsmA also represses the expression of cell wall-degrading enzymes in these bacteria (101,355). It is interesting to note that induction of the alarmone (p)ppGpp activates rsmB expression in P. atrosepticum, which is reminiscent of links between the Csr and the stringent response systems in E. coli and L. pneumophila (31,198,355,356).…”

“…In various species, CsrA/RsmA regulates environmental stress responses and regulatory factors that mediate stress responses, including the stringent response (31), osmotic resistance (91), heat resistance (91), oxidative stress (92)(93)(94), the global stress sigma factors RpoS (94)(95)(96) and AlgU (97), and the RNA chaperone Hfq (30). Global studies of CsrA/RsmA target RNAs and transcriptome effects suggest that CsrA/RsmA regulates the expression of many additional stress response genes that have not been studied in detail (31,56,(98)(99)(100)(101). Furthermore, the levels of the CsrA/RsmA-inhibitory sRNAs are controlled by several regulators that mediate stress responses, including DeaD/SrmB (10), Hfq (57,102), RpoS (32), AlgU (86), Crp (103), and (p)ppGpp/DksA (104)(105)(106).…”

The Global Response Regulator ExpA Controls Virulence Gene Expression through RsmA-Mediated and RsmA-Independent Pathways in Pectobacterium wasabiae SCC3193

“…The aRNA from each biological replicate of the four strains was coupled with one of three different dyes: HyPer 5 (Amersham), Cy3 (Amersham), and Alexa Fluor 488 (Invitrogen). Dye coupling was performed as described in our previous microarray study of SCC3193 (23).…”

“…Accordingly, the negative regulation of these virulence-related genes in Pectobacterium by RsmA has been well documented (7,8,15,24,25,28). Recently, we conducted a microarray analysis of the impact of an RsmA mutant on the global gene expression pattern in P. wasabiae SCC3193 (23). The resulting data revealed increased transcription of a number of genes involved in virulence, as well as fermentation and glycogen metabolism in the rsmA mutant.…”

“…The ExpS/ExpA TCS regulates large parts of the transcriptome of Pectobacterium via modulation of a posttranscriptional system consisting of RsmA, an RNA-binding protein that promotes RNA decay or stabilization, and a positive small regulatory RNA encoded by rsmB, which modulates the activity of RsmA (5,7,16,(23)(24)(25). The ExpS/ExpA TCS and its homologues in many gammaproteobacteria appear to primarily induce the transcription of genes encoding these small nontranslated RNAs (sRNAs); these include rsmB in P. wasabiae and Pectobacterium carotovorum and rsmX, rsmY, and rsmZ in Pseudomonas syringae DC3000 or Pseudomonas fluorescens (20,(25)(26)(27)(28)(29).…”