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, P-resorcylate, protocatechuate, p-hydroxybenzoate, and vanillin. Of these compQunds, only the latter five 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.

Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria

“…As described above, plants exude high levels of nutrients, and many of these act as chemoattractants for the bacteria. Different strains have been described to be positively chemotactic to sugars; amino acids; various dicarboxylic acids such as succinate, malate, fumarate; and aromatic compounds including shikimate, quinate, protocatechuate, vanillate, acetosyringone, gallate, catechol, and luteolin (15,34,62,201,371,372,414). One protein involved in sugar chemotaxis is ChvE of A. tumefaciens (Table 1), which is a chromosomally encoded sugar binding protein located in the periplasmic space (63).…”

Identification of the pcaRKF gene cluster from Pseudomonas putida: involvement in chemotaxis, biodegradation, and transport of 4-hydroxybenzoate

“…Chemotaxis and transport are two physiological functions that operate in this capacity, and a number of studies have shown that aromatic acids such as benzoate and 4-hydroxybenzoate are strong chemoattractants for Pseudomonas putida, as well as a number of other species of gram-negative bacteria including Agrobacterium spp. and rhizobia (19,20,31,39,40). However, very little is known about the characteristics of the presumed receptor proteins that are responsible for initial attractant recognition.…”

Agrobacterium-Mediated Genetic Transformation: History and Progress

“…These results indicated that the motility and chemotaxis are critical to A. tumefaciens infection under natural conditions (Hawes & Smith, 1989). Wild-type A. tumefaciens strains both containing and lacking Ti plasmid exhibited chemotaxis toward excised root tips from all plant species tested and toward root cap cells of pea and maize, suggesting that the majority of chemotactic responses in A. tumefaciens appear to be chromosomally encoded (Loake et al, 1988;Parke et al, 1987). However, the chemotactic response to some phenolic compounds, for example acetosyringone, which were identified as strong vir gene inducers, is controversial.…”