Thaxtomins,a family of phytotoxins produced by Streptomyces spp.,can causes plant cell necrosis at nanomolar concentrations.Thaxtomin A is the dominant form from Streptomyces scabies and has demonstrated herbicidal action.TxtE,a cytochrome P450 enzyme from S.scabies 87.22,catalyzes direct nitration of the indolyl moiety of Ltryptophan to L-4-nitrotryptophan using nitric oxide,dioxygen and NADPH,which is the key step of Thaxtomin A biosynthesis.