Vir-gene-inducing activities of hydroxycinnamic acid amides in Agrobacterium tumefaciens

Expression of Agrobacterium tumefaciens virulence genes and transformation of dicots by this organism are dependent upon host plant phenolic compounds . Several alkylsyringamides have recently been shown to be powerful inducer s of these vir-genes. These synthetic amides, and especially ethylsyringami de, are much stronger inducers than syringic acid. In this work, four alkyl amides derived from ferulic or sinapic acids were synthesized by a dicycloh exylcarbodiimide method and tested for their potential to induce vir-gene e xpression on A. tumefaciens strains harbouring virB::lacZ or virE::lacZ fus ion plasmids. Their effectiveness was compared to that of ethylsyringamide and tyraminylferulamide, a naturally occurring amide in plants. Whatever th e amine moiety of the amide (ethylamine, propylamine, tyramine or beta-alan ine ethyl ester) conjugation of the acid functional group clearly diminishe d the toxicity to the bacteria of the respective acid at high concentration and thereby increased the vir-inducing potential. However, none of the ind ucers tested exhibited higher activity than acetosyringone, the reference c ompound for vir-gene induction, with the exception of ethylsyringamide at c oncentrations above 1 mM. When tested on Agrobacterium tumefaciens strain A 348(pSM243cd), ethylferulamide and ethylsinapamide were more efficient than the corresponding phenolic acids but only above 100 mu M. (C) 1998 Elsevie r Science Ltd. All rights reserved.