Regulatory RNA as mediator in GacA/RsmA-dependent global control of exoproduct formation in Pseudomonas fluorescens CHA0.
In Pseudomonas fluorescens CHA0, an antagonist of root-pathogenic fungi, the GacS/GacA two-component system tightly controls the expression of antifungal secondary metabolites and exoenzymes at a posttranscriptional level, involving the RNA-binding protein and global regulator of secondary metabolism RsmA. This protein was purified from P. fluorescens, and RNA bound to it was converted to cDNA, which served as a probe to isolate the corresponding chromosomal locus, rsmZ. This gene encoded a regulatory RNA of 127 nucleotides and a truncated form lacking 35 nucleotides at the 3' end. Expression of rsmZ depended on GacA, increased with increasing population density, and was stimulated by the addition of a solvent-extractable extracellular signal produced by strain CHA0 at the end of exponential growth. This signal appeared to be unrelated to N-acyl-homoserine lactones. A conserved upstream element in the rsmZ promoter, but not the stress sigma factor RpoS, was involved in rsmZ expression. Overexpression of rsmZ effectively suppressed the negative effect of gacS and gacA mutations on target genes, i.e., hcnA (for hydrogen cyanide synthase) and aprA (for the major exoprotease). Mutational inactivation of rsmZ resulted in reduced expression of these target genes in the presence of added signal. Overexpression of rsmA had a similar, albeit stronger negative effect. These results support a model in which GacA upregulates the expression of regulatory RNAs, such as RsmZ of strain CHA0, in response to a bacterial signal. By a titration effect, RsmZ may then alleviate the repressing activity of RsmA on the expression of target mRNAs.
Heeb
Stephan
S
Laboratoire de Biologie Microbienne, Université de Lausanne, CH-1015 Lausanne, Switzerland.
Blumer
Caroline
C
Haas
Dieter
D
D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D001483:Base Sequence; D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D004269:DNA, Bacterial; D020689:Exopeptidases / Q000235:genetics; D005798:Genes, Bacterial; D005809:Genes, Regulator; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics; D016296:Mutagenesis; D009690:Nucleic Acid Conformation; D010088:Oxidoreductases / Q000235:genetics; D050891:Oxidoreductases Acting on CH-NH2 Group Donors; D011551:Pseudomonas fluorescens / Q000235:genetics / Q000378:metabolism*; D012329:RNA, Bacterial / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012808:Sigma Factor / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D004269:DNA, Bacterial; C091100:GacA protein, Bacteria; D009097:Multienzyme Complexes; D012329:RNA, Bacterial; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; C095468:RsmA protein, Erwinia carotovora; D012808:Sigma Factor; D014157:Transcription Factors; C069567:sigma factor KatF protein, Bacteria; C088386:homoserine lactone; D010088:Oxidoreductases; D050891:Oxidoreductases Acting on CH-NH2 Group Donors; C112800:glycine dehydrogenase (cyanide-forming); C074165:lemA protein, bacterial; C449646:AprA protein, Pseudomonas fluorescens; D020689:Exopeptidases; D015107:4-Butyrolactone