Regulatory roles of the GacS/GacA two-component system in plant-associated and other gram-negative bacteria.
The sensor kinase GacS and the response regulator GacA are members of a two-component system that is present in a wide variety of gram-negative bacteria and has been studied mainly in enteric bacteria and fluorescent pseudomonads. The GacS/GacA system controls the production of secondary metabolites and extracellular enzymes involved in pathogenicity to plants and animals, biocontrol of soilborne plant diseases, ecological fitness, or tolerance to stress. A current model proposes that GacS senses a still-unknown signal and activates, via a phosphorelay mechanism, the GacA transcription regulator, which in turn triggers the expression of target genes. The GacS protein belongs to the unorthodox sensor kinases, characterized by an autophosphorylation, a receiver, and an output domain. The periplasmic loop domain of GacS is poorly conserved in diverse bacteria. Thus, a common signal interacting with this domain would be unexpected. Based on a comparison with the transcriptional regulator NarL, a secondary structure can be predicted for the GacA sensor kinases. Certain genes whose expression is regulated by the GacS/GacA system are regulated in parallel by the small RNA binding protein RsmA (CsrA) at a posttranscriptional level. It is suggested that the GacS/GacA system operates a switch between primary and secondary metabolism, with a major involvement of posttranscriptional control mechanisms.
Heeb
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S
Laboratoire de Biologie Microbienne, Université de Lausanne, Switzerland.
Haas
D
D
D001426:Bacterial Proteins / Q000235:genetics*; D005809:Genes, Regulator; D006090:Gram-Negative Bacteria / Q000145:classification / Q000235:genetics*; D010944:Plants / Q000382:microbiology*; D011494:Protein Kinases / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*
D001426:Bacterial Proteins; C091100:GacA protein, Bacteria; D014157:Transcription Factors; D011494:Protein Kinases; C074165:lemA protein, bacterial