Abstract
The transcriptional regulator AmrZ is a global regulatory protein conserved within the pseudomonads. AmrZ can act both as a positive and a negative regulator of gene expression, controlling many genes implicated in environmental adaption. Regulated traits include motility, iron homeostasis, exopolysaccharides production and the ability to form biofilms. In Pseudomonas fluorescens F113, an amrZ mutant presents a pleiotropic phenotype, showing increased swimming motility, decreased biofilm formation and very limited ability for competitive colonization of rhizosphere, its natural habitat. It also shows different colony morphology and binding of the dye Congo Red. The amrZ mutant presents severely reduced levels of the messenger molecule cyclic-di-GMP (c-di-GMP), which is consistent with the motility and biofilm formation phenotypes. Most of the genes encoding proteins with diguanylate cyclase (DGCs) or phosphodiesterase (PDEs) domains, implicated in c-di-GMP turnover in this bacterium, appear to be regulated by AmrZ. Phenotypic analysis of eight mutants in genes shown to be directly regulated by AmrZ and encoding c-di-GMP related enzymes, showed that seven of them were altered in motility and/or biofilm formation. The results presented here show that in P. fluorescens, AmrZ determines c-di-GMP levels through the regulation of a complex network of genes encoding DGCs and PDEs.
Highlights
AmrZ is a highly conserved transcriptional regulator within the pseudomonads[1]
Among the twenty five genes transcriptionally activated by AmrZ, thirteen encode GGDEF, eight GGDEF-EAL, three EAL and one HD-GYP proteins. These results show that in F113, c-di-GMP levels are controlled by AmrZ in a complex regulatory network and that the low levels of c-di-GMP observed in the amrZ mutant are the result of a balance between activation and repression of a large number of genes encoding diguanylate cyclase (DGCs) and PDEs
AmrZ is a global regulator required for niche adaption in Pseudomonas fluorescens and P. aeruginosa
Summary
AmrZ is a highly conserved transcriptional regulator within the pseudomonads[1]. It was originally identified as a transcriptional activator of alginate production in Pseudomonas aeruginosa and named AlgZ2. Its implication in regulation of motility was extended by the finding of AmrZ as a repressor of flagellar synthesis in cystic fibrosis mucoid isolates of P. aeruginosa. This repression is exerted through transcriptional repression of the master regulator of flagella synthesis fleQ4. C-di-GMP levels are maintained by the opposing activity of diguanylate cyclases and phosphodiesterases[10] The former are proteins with GGDEF domains while the later are proteins containing EAL or HD-GYP domains[11,12,13]. We have previously shown by ChIP-Seq that in P. fluorescens F113, fourteen genes encoding proteins that contain GGDEF, EAL or HD-GYP domains are predicted to be targets of AmrZ1. We have used a combination of RNA-Seq and the phenotypic analysis of mutants affected in AmrZ and in c-di-GMP related genes, confirmed to be regulated by this global transcriptional regulator
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