title: Multiple-level regulation of 2,4-diacetylphloroglucinol production by the sigma regulator PsrA in Pseudomonas fluorescens 2P24.
abstract: BACKGROUND
  Pseudomonas fluorescens 2P24 is a rhizospheric bacterium that aggressively colonizes the plant roots. It produces the antibiotic 2,4-diacetylphoroglucinol (2,4-DAPG), which contributes to the protection of various crop plants against soil borne diseases caused by bacterial and fungal pathogens. The biosynthesis of 2,4-DAPG is regulated at the transcriptional level in the expression of the phlACBD operon as well as at the posttranscriptional level by the Gac/Rsm signal transduction pathway. However, the detailed mechanism of such regulation is not clear.
  
  
  RESULTS
  In this study, we identified a binding site for the sigma regulator PsrA in the promoter region of the phlA gene. Electrophoretic mobility shift experiments revealed direct and specific binding of PsrA to the phlA promoter region. Consistent with the fact that its binding site locates within the promoter region of phlA, PsrA negatively regulates phlA expression, and its inactivation led to significant increase in 2,4-DAPG production. Interestingly, PsrA also activates the expression of the sigma factor RpoS, which negatively regulates 2,4-DAPG production by inducing the expression of the RNA-binding protein RsmA.
  
  
  CONCLUSIONS
  These results suggest that PsrA is an important regulator that modulates 2,4-DAPG biosynthesis at both transcriptional and posttranscriptional levels.
authors.affiliation: Department of Plant Pathology, China Agricultural University, Beijing, People's Republic of China.
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Wu
authors.forename: Jiucheng
authors.initials: J
authors.lastname: Liu
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Liqun
authors.initials: L
authors.lastname: Zhang
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009876:Operon; D010696:Phloroglucinol / Q000031:analogs & derivatives / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011551:Pseudomonas fluorescens / Q000235:genetics / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D012988:Soil Microbiology; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C430183:PsrA protein, Pseudomonas; D012808:Sigma Factor; D014157:Transcription Factors; C059817:2,4-diacetylphloroglucinol; D010696:Phloroglucinol; D001616:beta-Galactosidase