rpoN1, but not rpoN2, is required for twitching motility, natural competence, growth on nitrate, and virulence of Ralstonia solanacearum

Abstract

The plant pathogen Ralstonia solanacearum has two genes encoding for the sigma factor σ54: rpoN1, located in the chromosome and rpoN2, located in a distinct “megaplasmid” replicon. In this study, individual mutants as well as a double mutant of rpoN were created in R. solanacearum strain GMI1000 in order to determine the extent of functional overlap between these two genes. By virulence assay we observed that rpoN1 is required for virulence whereas rpoN2 is not. In addition rpoN1 controls other important functions such twitching motility, natural transformation and growth on nitrate, unlike rpoN2. The rpoN1 and rpoN2 genes have different expression pattern, the expression of rpoN1 being constitutive whereas rpoN2 expression is induced in minimal medium and in the presence of plant cells. Moreover, the expression of rpoN2 is dependent upon rpoN1. Our work therefore reveals that the two rpoN genes are not functionally redundant in R. solanacearum. A list of potential σ54 targets was identified in the R. solanacearum genome and suggests that multiple traits are under the control of these regulators. Based on these findings, we provide a model describing the functional connection between RpoN1 and the PehR pathogenicity regulator and their dual role in the control of several R. solanacearum virulence determinants.

Involvement of ralfuranones in the quorum sensing signalling pathway and virulence of Ralstonia solanacearum strain OE1‐1

“…Ray et al . () revealed the broad conservation and stability of rpoN2 in the R. solanacearum species complex. They speculated that rpoN2 might be involved in the adaptation of the bacterium to a specific niche or environmental condition during its life cycle.…”

“…r54 (rpoN) is involved in the regulation of nitrogen metabolism, and subsequently affects many other biological activities in diverse Proteobacteria (Buck et al, 2000). In R. solanacearum, RpoN1, but not RpoN2, helps to regulate the transcription of twitching motility-related genes, and affects the nitrate assimilation pathway and virulence (Ray et al, 2015). Furthermore, rpoN2 expression is dependent on rpoN1.…”

“…rpoN1 and rpoN2). rpoN1 also influences the virulence of strain GMI1000 (Ray et al, 2015). Furthermore, the expression of solI and solR, which are associated with the SolI/R acyl-homoserine lactone QS system, depends on PhcA and RpoS (Flavier et al, 1997).…”

RpoN (σ 54 ) Is Required for Floc Formation but Not for Extracellular Polysaccharide Biosynthesis in a Floc-Forming Aquincola tertiaricarbonis Strain

“…It has also been revealed that some bacteria, including Xanthomonas oryzae pv. oryzae, Bradyrhizobium japonicum, Rhizobium etli, Burkholderia fungorum, and Ralstonia solanacearum, carry two copies of rpoN (31)(32)(33)(34), and four copies of rpoN are encoded in the genome of Rhodobacter sphaeroides (35). The four paralogues were designated rpoN1, rpoN2, rpoN3, and rpoN4, and their GϩC contents were 68.29%, 68.48%, 69.57%, and 56.13%, respectively.…”

The phenotype and pathogenicity of Ralstonia solanacearum transformed under prolonged stress of excessive exogenous nitrogen

“…The motility of R. solanacearum is reflected in two aspects: swimming motility and twitching motility. Swimming motility is controlled only by flagellum, but flagellum formation and movement in R. solanacearum are regulated by very complex genes and are influenced by cell concentrations and other signalling molecules, such as nitrate (Dalsing & Allen, ; Ray, Kumar, Peeters, Boucher, & Genin, ; Tans‐Kersten, Brown, & Allen, ). In general, changes in mobility contribute to the adaptation of R. solanacearum to a variety of environments.…”