Molecular Mechanisms of Two-Component System GacS/GacA in Plant-Pathogenic Bacteria

GacS/GacA global two-component regulatory systems are comprised of a membrane-bound environmental sensor, GacS, and a transcriptional response regulator, GacA. GacS/ GacA homologs have since been identified in some plant pathogenic bacterial. 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. 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.