Influence of phenolic compounds on Agrobacterium vir gene induction and onion gene transfer

Abstract Eight chalcones and benzalacetones were tested for their virulence induction on Agrobacterium tumefaciens . With one exception, they had a strong action, and in particular 4-(3,5-dimethoxy-4-hydroxy-phenyl)-but-3-en-2-one ( 10a ) was very effective with a virulence induction about 1.5–2 times that of acetosyringone ( AS ). When applied to Agrobacterium -mediated gene transfer of onion, both 10a and AS at 250 μM, led to increased gene transfer of between 25 and 35% when compared with the control. Many derivatives of AS were tested and the indispensable chemical functions required to induce vir genes were determined; for example, the presence of at least one methoxy group and a carbonyl group as in acetyl, aldehyde and acid functions. The most effective vir -inducing compound used was the original AS with two methoxy groups and an acetyl function. By testing the corresponding β-glucosides and glucosyl esters (from acids), we established that a phenolic function was also essential for virulence induction. These glucosides led to a decreased toxicity to the bacteria in relation to the original product. However, the presence of a β-glucosylated phenol function led to the total loss of vir induction while the corresponding esters, particularly the glucosyl sysingate ester, conserved a good vir induction.