Mutations in the regulatory gene hrpG of Xanthomonas campestris pv. vesicatoria result in constitutive expression of all hrp genes

hrpG is a key regulatory gene for transcriptional activation of pathogenici ty genes (hrp) of Xanthomonas campestris pv. vesicatoria. We identified thr ee mutations in hrpG which render hrp gene expression constitutive in norma lly suppressing medium. The mutations in hrpG result in novel amino acid su bstitutions compared to mutations in related proteins, such as OmpR. In add ition, mutated hrpG enhances the timing and intensity of plant reactions in infection assays.