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RpoN (sigma54) controls production of antifungal compounds and biocontrol activity in Pseudomonas fluorescens CHA0.
Molecular Plant-Microbe Interactions
Pseudomonas fluorescens CHA0 is an effective biocontrol agent of root diseases caused by fungal pathogens. The strain produces the antibiotics 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT) that make essential contributions to pathogen suppression. This study focused on the role of the sigma factor RpoN (sigma54) in regulation of antibiotic production and biocontrol activity in P. fluorescens. An rpoN in-frame-deletion mutant of CHAO had a delayed growth, was impaired in the utilization of several carbon and nitrogen sources, and was more sensitive to salt stress. The rpoN mutant was defective for flagella and displayed drastically reduced swimming and swarming motilities. Interestingly, the rpoN mutant showed a severalfold enhanced production of DAPG and expression of the biosynthetic gene phlA compared with the wild type and the mutant complemented with monocopy rpoN+. By contrast, loss of RpoN function resulted in markedly lowered PLT production and plt gene expression, suggesting that RpoN controls the balance of the two antibiotics in strain CHA0. In natural soil microcosms, the rpoN mutant was less effective in protecting cucumber from a root rot caused by Pythium ultimum. Remarkably, the mutant was not significantly impaired in its root colonization capacity, even at early stages of root infection by Pythium spp. Taken together, our results establish RpoN for the first time as a major regulator of biocontrol activity in Pseudomonas fluorescens.
Amino Acid Sequence, Anti-Bacterial Agents/metabolism, Antifungal Agents/metabolism, Base Sequence, Chromosomes, Bacterial/genetics, DNA, Bacterial/genetics, DNA-Binding Proteins/chemistry, DNA-Binding Proteins/genetics, DNA-Directed RNA Polymerases/chemistry, DNA-Directed RNA Polymerases/genetics, Genes, Bacterial, Molecular Sequence Data, Mutation, Pest Control, Biological, Phenols, Phloroglucinol/analogs & derivatives, Phloroglucinol/metabolism, Plant Diseases/microbiology, Plants/microbiology, Plasmids/genetics, Pseudomonas fluorescens/genetics, Pseudomonas fluorescens/growth & development, Pyrroles, RNA Polymerase Sigma 54, Sigma Factor/chemistry, Sigma Factor/genetics, Symbiosis
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