Nuclear factors GT-1 and 3AF1 interact with multiple sequences within the promoter of the Tdc gene from Madagascar periwinkle: GT-1 is involved in UVlight-induced expression

Plant secondary metabolites of the terpenoid indole alkaloid (TIA) class co mprise several compounds with pharmaceutical applications. A key step in th e TIA biosynthetic pathway is catalysed by the enzyme tryptophan decarboxyl ase (TDC), which channels the primary metabolite tryptophan into TIA metabo lism. In Catharanthus roseus (Madagascar periwinkle), the Tdc gene is expre ssed throughout plant development. Moreover, Tdc gene expression is induced by external stress signals, such as fungal elicitor and UV light. In a pre vious study of Tdc promoter architecture in transgenic tobacco it was shown that the -538 to -112 region is a quantitative determinant for the express ion level in different plant organs. Within this sequence one particular re gion (-160 to -99) was identified as the major contributor to basal express ion and another region (-99 to -37) was shown to be required for induction by fungal elicitor. Here, the in vitro binding of nuclear factors to the -5 72 to -37 region is described. In extracts from tobacco and C. roseus, two binding activities were detected that could be identified as the previously described nuclear factors GT-1 and 3AF1, based on their mobility and bindi ng characteristics. Both factors appeared to interact with multiple regions in the Tdc promoter. Mutagenesis of GT-I binding sites in the Trk promoter did not affect the basal or elicitor-induced expression levels. However, i nduction of the Tdc promoter constructs by UV light was significantly lower , thereby demonstrating a functional role for GT-1 in the induction of Tdc expression by UV light.