AN AGROBACTERIUM 2-COMPONENT REGULATORY SYSTEM FOR THE DETECTION OF CHEMICALS RELEASED FROM PLANT WOUNDS

Crown gall tumorigenesis by Agrobacterium tumefaciens requires the co-ordinate transcriptional induction of a set of pathogenesis genes. At least three classes of environmental stimuli act synergistically to induce these genes: (i) monocyclic aromatic hydrocarbons such as acetosyringone, coniferyl alcohol, and vanillin, (ii) neutral or acidic monosaccharides such as glucose and glucuronic acid, and (iii) acidic pH. Three proteins are required to sense and respond to these stimuli: (i) VirA, a transmembrane sensory protein and histidine protein kinase, (ii) VirG, a transcriptional activator which is phosphorylated by phosphoryl VirA, and (iii) ChvE, a periplasmic sugar-binding protein. VirA and VirG are members of the so-called two-component family of regulatory proteins. This regulatory system continues to offer new discoveries in the areas of signal transduction, host-microbe interactions, and host range.