Multiple CsrA Proteins Control Key Virulence Traits inPseudomonas syringaepv.tomatoDC3000

Abstract

The phytopathogenic bacterium Pseudomonas syringae pv. tomato DC3000 has a complex Gac-rsm global regulatory pathway that controls virulence, motility, production of secondary metabolites, carbon metabolism, and quorum sensing. However, despite the fact that components of this pathway are known, their physiological roles have not yet been established. Regarding the CsrA/RsmA type proteins, five paralogs, three of which are well conserved within the Pseudomonas genus (csrA1, csrA2, and csrA3), have been found in the DC3000 genome. To decipher their function, mutants lacking the three most conserved CsrA proteins have been constructed and their physiological outcomes examined. We show that they exert nonredundant functions and demonstrate that CsrA3 and, to a lesser extent, CsrA2 but not CsrA1 alter the expression of genes involved in a variety of pathways and systems important for motility, exopolysaccharide synthesis, growth, and virulence. Particularly, alginate synthesis, syringafactin production, and virulence are considerably de-repressed in a csrA3 mutant, whereas growth in planta is impaired. We propose that the linkage of growth and symptom development is under the control of CsrA3, which functions as a pivotal regulator of the DC3000 life cycle, repressing virulence traits and promoting cell division in response to environmental cues.

Homologues of the RNA binding protein RsmA in Pseudomonas syringae pv. tomato DC3000 exhibit distinct binding affinities with non‐coding small RNAs and have distinct roles in virulence

“…; Table ). We also observed that mutation of the rsmA1 gene alone did not affect GABA utilization, protease activity and pyoverdine production (except a minor increase in motility) (Figs and ), suggesting that RsmA1 plays a very minimal role, as previously reported (Ferreiro et al , ). Based on these results, we mainly focused on RsmA2, RsmA3 and RsmA4 for the majority of our studies.…”

“…RsmA (CsrA) plays a critical role in virulence among many pathogenic bacteria (Ancona et al , ; Andrade et al , ; Barnard et al , ). It has been reported that deletion of a single csrA gene in Pst DC3000 did not affect virulence, but bacterial growth was reduced in the csr2 and csr3 mutants (Ferreiro et al , ). In our study, we confirmed that deletion of a single rsmA gene did not change its ability to cause disease.…”

“…In a previous report, three paralogues, i.e. csrA1 , csrA2 and csrA3 in Pst DC3000, were evaluated for their roles in motility, alginate biosynthesis, syringafactin production and virulence, and the authors concluded that CsrA1 to CsrA3 were not required for virulence (Ferreiro et al , ). However, in our study we demonstrated that RsmA2 and RsmA3 were required for virulence in Pst DC3000 and bacterial growth in planta , and RsmA4 might also play a minor role in virulence.…”

“…They showed that CsrA2 (RsmA2) is the most conserved member among 250 prokaryotic genomes examined, and CsrA3 (RsmA3) is nearly identical to CsrA2, but is present only in the Pseudomonas fluorescens group (RsmE). They further reported that CsrA3 and CsrA2 were found to play roles in motility, syringafactin and alginate production, and promote growth in planta, but not symptom development (Ferreiro et al , ). Here, we labelled these CsrA proteins in Pst DC3000 as RsmA proteins because deduced amino acids of RsmA proteins in Pst DC3000 shared relatively higher identities and similarities to RsmA proteins from other Pseudomonas strains than to CsrA proteins from E. coli and Erwinia species (Fig.…”

“…However, the molecular mechanism and virulence‐related target genes of the CsrA/RsmA proteins in Pst DC3000 remain elusive. A recent study identified five alleles of CsrA (RsmA) proteins present in Pst DC3000 and characterized three single mutants ( csrA1 to csrA3 ) (Ferreiro et al , ). They showed that CsrA2 (RsmA2) is the most conserved member among 250 prokaryotic genomes examined, and CsrA3 (RsmA3) is nearly identical to CsrA2, but is present only in the Pseudomonas fluorescens group (RsmE).…”