Contribution of a lectin, LecM, to the quorum sensing signalling pathway of Ralstonia solanacearum strain OE1‐1

Abstract

Summary The soil‐borne bacterium Ralstonia solanacearum invades the roots and colonizes the intercellular spaces and then the xylem. The expression of lecM , encoding a lectin LecM, is induced by an OmpR family response regulator HrpG in R. solanacearum strain OE1‐1. LecM contributes to the attachment of strain OE1‐1 to the host cells of intercellular spaces. OE1‐1 produces methyl 3‐hydroxymyristate (3‐OH MAME) through a methyltransferase (PhcB) and extracellularly secretes the chemical as a quorum sensing (QS) signal, which activates QS. The expression of lecM is also induced by the PhcA virulence regulator functioning through QS, and the resulting LecM is implicated in the QS‐dependent production of major exopolysaccharide EPS I and the aggregation of OE1‐1 cells. To investigate the function of LecM in QS, we analysed the transcriptome of R. solanacearum strains generated by RNA sequencing technology. In the lecM mutant, the expression of positively QS‐regulated genes and negatively QS‐regulated genes was down‐regulated (by >90%) and up‐regulated (by ~60%), respectively. However, phcB and phcA in the lecM mutant were expressed at levels similar to those in strain OE1‐1. The lecM mutant produced significantly less ralfuranone and exhibited a significantly greater swimming motility, which were positively and negatively regulated by QS, respectively. In addition, the extracellular 3‐OH MAME content of the lecM mutant was significantly lower than that of OE1‐1. The application of 3‐OH MAME more strongly increased EPS I production in the phcB ‐deleted mutant and strain OE1‐1 than in the lecM mutant. Thus, the QS‐dependent production of LecM contributes to the QS signalling pathway.

Major exopolysaccharide, EPS I, is associated with the feedback loop in the quorum sensing of Ralstonia solanacearum strain OE1‐1

“…We first analysed the transcriptomes of R. solanacearum strains, the Δ epsB mutant, the phcB ‐deletion mutant Δ phcB (Kai et al , ), the phcA ‐deletion mutant Δ phcA (Mori et al , ) and the strain OE1‐1 (Kanda et al , ), which were cultured in one‐quarter‐strength M63 medium (1/4 M63; Cohen and Rickenberg, ) until the optical density at 600 nm (OD 600 ) was 0.3. RNA sample preparation and sequencing were performed as previously described (Hayashi et al ., ). RNA‐Seq data mapping and analyses were performed with an Illumina HiSeq 2000 system (Illumina, Madison, WI, USA) according to the protocols of Hayashi et al .…”

“…RNA‐Seq data mapping and analyses were performed with an Illumina HiSeq 2000 system (Illumina, Madison, WI, USA) according to the protocols of Hayashi et al . (). For each strain, we conducted two biologically independent experiments.…”

“…Furthermore, functional PhcA induces the expression of lecM , encoding the lectin LecM (Meng et al , ; Mori et al , ). LecM affects the extracellular stability of 3‐OH MAME, contributing to the phc QS signalling pathway (Hayashi et al , ).…”

“…The transcriptome analysis showed that deletion of epsB led to significantly reduced expression levels of lecM . LecM affects the extracellular stability of 3‐OH MAME, contributing to the phc QS signalling pathway (Hayashi et al , ). We next assayed the extracellular 3‐OH MAME contents of R. solanacearum strains Δ epsB , epsB ‐comp and OE1‐1.…”

Modulation of Quorum Sensing as an Adaptation to Nodule Cell Infection during Experimental Evolution of Legume Symbionts

“…EfpR represses the Rsc3146 to -3148 genes. In an efpR mutant, the strong induction of Rsc3146 to -3148 genes affects a large part of the PhcA regulon either by modulating PhcA activity, by acting on the expression of some PhcA target genes, or by inhibiting one of the positive feedback loops of activation of PhcA(16,33). Dashed lines indicate potential indirect effects.…”