An Agrobacterium signal compound from grapevine cultivars

Two host-plant-derived phenolic compounds (acetosyringone and α-hydroxyacetosyringone), which act as chemical signals for wide host range strains of Agrobacterium tumefaciens, have remained the only virulence (vir) gene inducing compounds identified from host plant tissues. Here we report the isolation of a vir-inducing phenolic compound from a number of Vitis cultivars, including a known host for limited host range A. tumefaciens, and its identification as syringic acid methyl ester (3,5-dimethoxy-4-hydroxybenzoic acid methyl ester). The presence of this compound in wound exudates does not provide a simple explanation for host range limitation of grapevine strains as it induces vir gene expression in both limited and wide host range strains of Agrobacterium.