Swimming against the tide: chemotaxis in Agrobacterium.

Chemotaxis in bacteria is an excellent model for signal transduction processes. In Agrobacterium tumefaciens, the causative agent of crown gall tumour on wounded plants, it is a vital part of the organism's biology. A chromosomally-determined chemotaxis system causes the bacterium to be attracted into the rhizosphere by chemoattractants in plant exudates. By interfacing with this system, the multifunctional products of two Ti-plasmid encoded genes, virA and virG, allow the sensing of specific wound phenolics such as acetosyringone. This attracts Ti-plasmid harbouring A. tumefaciens to wound sites, where the higher acetosyringone concentrations lead to virA and virG-mediated induction of the vir-genes. The products of the induced genes, act in concert to effect transfer of the T-DNA to the plant cell.