AUTHOR=Li Peng , Cao Xiulan , Zhang Liwen , Lv Mingfa , Zhang Lian-Hui 

TITLE=PhcA and PhcR Regulate Ralsolamycin Biosynthesis Oppositely in Ralstonia solanacearum

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.903310

DOI=10.3389/fpls.2022.903310

ISSN=1664-462X

ABSTRACT=<p>Ralsolamycin, one of secondary metabolites in <italic>Ralstonia solanacearum</italic>, is known to be involved in crosstalk between <italic>R. solanacearum</italic> and fungi. Ralsolamycin formation is catalyzed by two-hybrid synthetases of RmyA (non-ribosomal peptide synthetase) and RmyB (polyketide synthase). A methyltransferase PhcB catalyzes formation of 3-OH MAME or 3-OH PAME, signals for the quorum sensing (QS) in <italic>R. solanacearum</italic>, while PhcB positively modulates ralsolamycin biosynthesis. A two-component system of PhcS and PhcR can response these QS signals and activate <italic>phcA</italic> expression. Here, we experimentally demonstrated that deletion of <italic>phcA</italic> (Δ<italic>phcA</italic>) substantially impaired the ralsolamycin production and expression of <italic>rmyA</italic> and <italic>rmyB</italic> in <italic>R. solanacearum</italic> strain EP1, and failed to induce chlamydospore formation of plant fungal pathogen <italic>Fusarium oxysporum</italic> f. <italic>cubense</italic> (stran FOC4). However, deletion of <italic>phcR</italic> significantly increased ralsolamycin production and expression of <italic>rmyA</italic> and <italic>rmyB</italic>, and <italic>phcR</italic> mutants exhibited enhanced ability to induce chlamydospore formation of FOC4. Results of the electrophoretic mobility shift assay suggested that both PhcA and PhcR bind to promoter of <italic>rmy</italic> operon. Taken together, these results demonstrated that both PhcA and PhcR bind to promoter of <italic>rmy</italic> operon, but regulate ralsolamycin biosynthesis in an opposite way. It could extend our knowledge on the sophisticated regulatory networks of ralsolamycin biosynthesis in <italic>R. solanacearum</italic>.</p>