Modulation of Inter-kingdom Communication by PhcBSR Quorum Sensing System in Ralstonia solanacearum Phylotype I Strain GMI1000

Abstract

Ralstonia solanacearum is a ubiquitous soil-borne plant pathogenic bacterium, which frequently encounters and interacts with other soil cohabitants in competition for environmental niches. Ralsolamycin, which is encoded by the rmy genes, has been characterized as a novel inter-kingdom interaction signal that induces chlamydospore development in fungi. In this study, we provide the first genetic evidence that the rmy gene expression is controlled by the PhcBSR quorum sensing (QS) system in strain GMI1000. Mutation of phcB could lead to significant reduction of the expression levels of the genes involved in ralsolamycin biosynthesis. In addition, both the phcB and rmy mutants were attenuated in induction of chlamydospore formation in Fusarium oxysporum f. cubense and diminished in the ability to compete with the sugarcane pathogen Sporisorium scitamineum. Agreeable with the pattern of QS regulation, transcriptional expression analysis showed that the transcripts of the rmy genes were increased along with the increment of the bacterial population density. Taken together, the above findings provide new insights into the regulatory mechanisms that the QS system involves in governing the ralsolamycin inter-kingdom signaling system.

Anthranilic acid from Ralstonia solanacearum plays dual roles in intraspecies signalling and inter-kingdom communication

“…1 , 3 ). Some previous studies have also revealed that R. solanacearum employs QS to control the production of ralsolamycin to achieve a fitness advantage in inter-kingdom competition [ 24 – 26 ]. Our new findings suggested that complicated mechanisms have evolved in R. solanacearum to achieve for a competitive advantage in the microbial community.…”

“…The biosynthesis of ralsolamycin in R. solanacearum is modulated by the two nonribosomal peptide synthetases, RmyA and RmyB [ 25 ]. Interestingly, our previous study revealed that the expression of rmyAB was controlled by the phcBSR QS system [ 26 ], suggesting that QS plays an important role in inter-kingdom communication between R. solanacearum and fungi. In this study, we showed that anthranilic acid produced by TrpEG in R. solanacearum inhibits sexual mating and hypha formation in Sporisorium scitamineum .…”

PhcA and PhcR Regulate Ralsolamycin Biosynthesis Oppositely in Ralstonia solanacearum

“…In the present study, mutants were generated with the pK18mobsacB based homologue recombination, by which target genes were in-frame deleted as described previously ( Li et al, 2017 ). In brief, coding sequence of target genes was removed by the joint PCR, which conjugated both ends of flanking DNA fragments.…”

“…R. solanacearum strains and F. oxysporum f. cubense FOC4 were dropped onto same PDA agar plate and incubated at 28°C for about eight days. When two kinds of colonies interweaved each other, the FOC4 mycelia surrounded the interaction zones at about 1 cm were harvested and subjected for chlamydospore counting under microscope ( Li et al, 2017 ).…”

“…We previously demonstrated that deletion of phcB drastically decreased expression of rmyA and rmyB and impaired chlamydospores formation in a Fusarium oxysporum f. cubense (FOC4), soil-borne phytopathogens that exhibits attenuated antifungal activity against Sporisorium scitamineum ( Li et al, 2017 ). In addition, expression of rmyA and rmyB is downregulated with phcA deletion ( Perrier et al, 2018 ).…”