Structure of Ralsolamycin, the Interkingdom Morphogen from the Crop Plant Pathogen Ralstonia solanacearum

Abstract

Ralsolamycin, an inducer of chlamydospore formation in fungi, was recently reported from the plant pathogenic bacterium Ralstonia solanacearum. Although interpretation of tandem mass data and bioinformatics enabled a preliminary chemical characterization, the full structure of ralsolamycin was not resolved. We now report the recovery of this secondary metabolite from an engineered R. solanacearum strain. The structure of ralsolamycin was elucidated by extensive spectroscopic analyses. Chemical derivatization as well as bioinformatics were used to assign the absolute stereochemistry. Our results identified an erroneous genome sequence, thereby emphasizing the value of chemical methods to complement bioinformatics-based procedures in natural product research.

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

“…A previous study showed that R. solanacearum produces ralsolamycin to induce chlamydospore formation in fungi [ 24 ]. As both R. solanacearum and S. scitamineum are plant pathogens, we investigated whether competition exists between the two pathogens.…”

“…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.…”

“…Small molecule signals are increasingly recognized as important interspecies or inter-kingdom communication signals in microbial communities [ 23 ]. Ralsolamycin from R. solanacearum has been identified as an inducer of chlamydospore formation in fungi such as Ascomycetes , Basidiomycetes and Zygomycetes [ 24 ]. The biosynthesis of ralsolamycin in R. solanacearum is modulated by the two nonribosomal peptide synthetases, RmyA and RmyB [ 25 ].…”

Near-Complete Genome Sequence of Ralstonia solanacearum T523, a Phylotype I Tomato Phytopathogen Isolated from the Philippines

“…The chromosome encodes a complete gene cluster for micacocidin biosynthesis, a siderophore utilizing a hybrid pathway of nonribosomal peptide synthetase, and a type I iterative polyketide synthase ( 11 ). The megaplasmid encodes genes involved in the production of the antibiotic lipopeptide ralstonin/ralsolamycin, with established phytotoxic ( 12 , 13 ) and antifungal ( 12 , 14 ) activities, and a putative bacteriocin. Biosynthetic gene clusters for exopolysaccharide, terpene, and homoserine lactone production were detected.…”

Conserved Responses in a War of Small Molecules between a Plant-Pathogenic Bacterium and Fungi

“…Although R. solanacearum has been studied primarily because of its severe impacts on plant hosts, it has recently been shown to impact plant-prokaryote community composition ( 5 ), and it also interacts intimately with many soil fungi through volatile and diffusible signaling ( 6 – 8 ). The lipopeptide ralsolamycin (synonym ralstonin A), produced by a hybrid polyketide synthase/nonribosomal peptide synthetase (PKS-NRPS) biosynthetic gene cluster ( rmy ) ( 7 , 9 , 10 ), was shown to induce chlamydospore formation in a phylogenetically diverse panel of plant-associated and/or soil-inhabiting fungi representing members of the Mucoromycota, Ascomycota, and Basidiomycota ( 7 ). Among the assayed fungi were members of the genus Fusarium .…”