Chemotaxis to plant phenolic inducers of virulence genes is constitutively expressed in the absence of the Ti plasmid in Agrobacterium tumefaciens

Abstract

The virulence (vir) genes are required in the early stages of plant tumor formation and are located together on the tumor-inducing (Ti) plasmid in Agrobacterium tumefaciens. Five of the vir genes are expressed inducibly in response to the following monocyclic phenolic compounds: acetosyringone, catechol, gallate, beta-resorcylate, protocatechuate, p-hydroxybenzoate, and vanillin. Of these compounds, only the latter six, excluding vanillin [corrected] served as chemoattractants and only the latter three served as growth substrates for A. tumefaciens A348. Strain A136, isogenic except for lack of the Ti plasmid, demonstrated chemotactic behavior and nutritional capabilities similar to those of strain A348. The chemotactic response to the vir gene inducers was expressed constitutively.