In vitro inhibition of shikimate hydroxycinnamoyltransferase by acibenzolar acid, the first metabolite of the plant defence inducer acibenzolar-S-methyl

Acibenzolar acid, the first metabolite formed in planta from defence inducer acibenzolar-S-methyl (ASM), has been shown to be an inhibitor of enzyme shikimate hydroxycinnamoyltransferase (HST), extracted grapevine or tobacco cell suspension cultures. Using a purified recombinant Arabidopsis thaliana HST, inhibition was found competitive, acibenzolar acid binding reversibly site HST:p-coumaroyl-CoA complex, with Ki value 250 μM. The other hydroxycinnamoyltransferases tested course this study, using either hydroxypalmitic putrescine, tyramine, quinic as acyl acceptors were not, only slightly, inhibited by acid. To understand specificity interaction we analyzed structure-activity relationship series benzoic analogues, AtHST substrates inhibitors. This analysis confirmed previously published data on substrate flexibility HST and demonstrated that both carboxyl group thiadiazole moiety are playing important role site. which cannot form ester bond p-coumaric however less potent than protocatechuic 3-hydroxybenzoic acids, used HST. Our results show is probably directly linked promiscuity unlikely play direct defence-inducing properties ASM plants.