Involvement of ralfuranones in the quorum sensing signalling pathway and virulence of Ralstonia solanacearum strain OE1‐1. (9th March 2017)

• Record Type: Journal Article
• Authors: Mori, Yuka; Ishikawa, Shiho; Ohnishi, Hideyuki; Shimatani, Mika; Morikawa, Yukino; Hayashi, Kazusa; Ohnishi, Kouhei; Kiba, Akinori; Kai, Kenji; Hikichi, Yasufumi
• Is Part Of: Molecular plant pathology. Volume 19:Number 2(2018)
• Page Start: 454
• Page End: 463
• Publication Date: 2017-03-09
• Subjects: quorum sensing -- ralfuranones -- Ralstonia solanacearum -- soil‐borne -- plant‐pathogenic bacterium -- virulence; Plant diseases -- Molecular aspects -- Periodicals; Plant-pathogen relationships -- Molecular aspects -- Periodicals; 571.936
• DOI: 10.1111/mpp.12537
• Languages: English
• ISSNs: 1464-6722

Abstract

Summary: The soil‐borne, plant‐pathogenic Ralstonia solanacearum strain OE1‐1 produces and secretes methyl 3‐hydroxymyristate (3‐OH MAME) as a quorum sensing (QS) signal, which contributes to its virulence. A global virulence regulator, PhcA, functioning through the QS system, positively regulates the expression of ralA, which encodes furanone synthase, to produce aryl‐furanone secondary metabolites, ralfuranones. A ralfuranone‐deficient mutant (Δ ralA ) is weakly virulent when directly inoculated into tomato xylem vessels. To investigate the functions of ralfuranones, we analysed R. solanacearum transcriptome data generated by RNA sequencing technology. Δ ralA expressed phcB, which is associated with 3‐OH MAME production, and phcA at levels similar to those in strain OE1‐1. In addition, Δ ralA exhibited down‐regulated expression of more than 90% of the QS positively regulated genes, and up‐regulated expression of more than 75% of the QS negatively regulated genes. These results suggest that ralfuranones affect the QS feedback loop. Ralfuranone supplementation restored the ability of Δ ralA cells to aggregate. In addition, ralfuranones A and B restored the swimming motility of Δ ralA to wild‐type levels. However, the application of exogenous ralfuranones did not affect the production of the major exopolysaccharide, EPS I, in Δ ralA . Quantitative real‐time polymerase chain reaction assays revealed that the deletion of ralA results in the down‐regulated expression of vsrAD and vsrBC, which encode a sensor kinase and a response regulator, respectively, in the two‐component regulatory systems that influence EPS I production. The application of ralfuranone B restored the expression of these two genes. Overall, our findings indicate that integrated signalling via ralfuranones influences the QS and virulence of R. solanacearum .