Synergistic Action of Phenolic Signal Compounds and Carbohydrates in the Induction of Virulence Gene Expression of Agrobacterium tumefaciens.

Virulence (vir) gene expression of Agrobacterium tumefaciens is activated by plant phenolic compounds such as alpha-hydroxyacetosyringone (HOAS), acetosyringone (AS), methyl syringate, coniferyl alcohol and sinapyl alcohol. Inositol was found to be a potentiating factor of vir-inducing activity, which enhanced the vir-inducing activity of AS and HOAS in a synergistic manner, in particular at a low concentrations of AS and HOAS. Of the other sugars tested D-glucose, L-rhamnose, D-xylose and D-galacturonic acid, the main components of plant cell wall polysaccharides, remarkedly potentiated the vir-inducing activity of AS, indicating the cooperative action of the signal compounds and sugars in Agrobacterium infection to plants.