Ralfuranone Biosynthesis in Ralstonia solanacearum Suggests Functional Divergence in the Quinone Synthetase Family of Enzymes

Abstract

Ralstonia solanacearum is a destructive crop plant pathogen and produces ralfuranone, i.e., a monophenyl-substituted furanone. Extensive feeding experiments with (13)C-labeled L-phenylalanine now proved that all carbon atoms of the heterocycle derive, after deamination, from this aromatic amino acid. A genetic locus was identified which encodes the aminotransferase RalD and the furanone synthetase RalA. The latter is a tridomain nonribosomal peptide synthetase (NRPS)-like enzyme which was characterized (1) biochemically by the ATP-pyrophosphate exchange assay, and (2) genetically through gene inactivation and transcriptional analysis in axenic culture and in planta. This is the first study to our knowledge on the biochemical and genetic basis of R. solanacearum secondary metabolism. It implies new chemistry for NRPSs, as RalA-mediated biosynthesis requires C-C-bond and subsequent C-O-bond formation to establish the furanone ring system.

Application of an Efficient Gene Targeting System Linking Secondary Metabolites to their Biosynthetic Genes in Aspergillus terreus

“…Recently the NRPS-like genes responsible for the biosynthesis of ralfuranone and microperfuranone, natural products that shares structural similarity with butyrolactones and aspulvinones were reported. 15, 16 Our data suggest that the biosynthetic route of butyrolactones and aspulvinones are similar to that of ralfuranone and microperfuranone.…”

Regulation Involved in Colonization of Intercellular Spaces of Host Plants in Ralstonia solanacearum

“…The production of transaminase and furanone synthase, which are encoded by ralD and ralA , respectively, depends on functional PhcA via the phc QS system. Both the transaminase and furanone synthase are involved in the biosynthesis of ralfuranone I (Schneider et al, 2009; Wackler et al, 2011; Kai et al, 2014). Ralfuranone I is non-enzymatically converted into ralfuranone B in the supernatant (Kai et al, 2016).…”

Spatial regulation of a common precursor from two distinct genes generates metabolite diversity

“…It is usually expected that core synthetic genes, in a given species, are behind the biosynthesis of different core intermediates, as demonstrated in a study showing that all individual NRPKS in A. nidulans generate a unique PKS product. 5 Phylogenetic analysis, using the protein sequences of those NRPS-like homologs obtained from the Broad Institute Aspergillus comparative database, revealed several other characterized NRPS-like homologs including TdiA (terrequinone A biosynthesis in A. nidulans ), 8 RalA (ralfuranone biosynthesis in Ralstonia solanacearum ), 28 MicA (microperfuranone biosynthesis in A. nidulans ), 29 AtqA (asterriquinone biosynthesis in A. terreus ), 7 BtyA (butyrolactone biosynthesis in A. terreus ), 7 and EchA (echosides biosynthesis in Streptomyces sp. LZ35) 30 (Fig.…”