Specificity of signal compounds detected by Agrobacterium tumefaciens

Agrobacterium tumefaciens is known to respond to the presence of certain phenolic compounds by expressing genes prerequisite for transformation of plant cells. One report has described the isolation and identification of virulence-inducing acetosyringone and hydroxyacetosyringone from a host plant. Since these compounds have never previously been reported from plant tissues and are not likely of widespread occurrence, it seems unlikely that these are the only signal compounds for this wide host range pathogen. We report here the structure-activity specificity of vir-induction, and present results which indicate that Agrobacterium is capable of detecting compounds which are ubiquitous or at least widespread amongst its host range. Also, the vir-inducing activities of the lignin precursors coniferyl and sinapyl alcohols are presented and discussed in terms of the biology of Agrobacterium.