THE CHROMOSOMAL RESPONSE REGULATORY GENE CHVI OF AGROBACTERIUM-TUMEFACIENS COMPLEMENTS AS ESCHERICHIA-COLI PHOB MUTATION AND IS REQUIRED FOR VIRULENCE

In an effort to identify the Agrobacterium tumefaciens phosphate regul atory gene(s), we isolated a clone from an A. tumefaciens cosmid libra ry that restored regulated alkaline phosphatase activity to an Escheri chia coli phoB mutant. The gene that complemented phoB was localized b y subcloning and deletion analysis, and the DNA sequence was determine d. An open reading frame, denoted chvI, was identified that encoded a predicted protein with amino acid similarity to the family of bacteria l response regulators and 35% identity to PhoB. Surprisingly, an A. tu mefaciens chvI mutant showed normal induction of phosphatase activity and normal virG expression when grown in phosphate-limiting media. How ever, this mutant was unable to grow in media containing tryptone, pep tone, or Casamino Acids and was also more sensitive than the wild type to acidic extracellular pH. This mutant was avirulent on Kalanchoe di agremontiana and was severely attenuated in vir gene expression. The p H-inducible expression of virG was also abolished. Growth of the chvI mutant was inhibited by K. diagremontiana wound sap, suggesting that a virulence may be due, in part, to the inability of this mutant to surv ive the plant wound environment.