Elicitor-responsive promoter regions in the tryptophan decarboxylase gene from Catharanthus roseus

The tryptophan decarboxylase (Tdc) gene from Catharanthus roseus (Madagasca r periwinkle) encodes a key enzyme in biosynthesis of terpenoid indole alka loids. The expression of the Tdc gene is transcriptionally induced by funga l elicitors. Tdc upstream sequences from -1818 to +198 relative to the tran scriptional start site were functionally analysed to identify cis-acting el ements that determine basal expression or respond to elicitor. In a loss-of -function analysis promoter derivatives with 5' or internal deletions fused to the gusA reporter gene were analysed in transgenic tobacco plants. Wher eas promoter activity dropped considerably following deletion down to -160, this short promoter derivative was still elicitor-responsive Subsequently, the -160 to -37 region was further studied by gain-of-function experiments , in which subfragments were tested as tetramers cloned on two different tr uncated promoters. Combination of the data resulted in the identification o f three functional regions in the -160 promoter. The region between -160 to -99 was shown to act as the main transcriptional enhancer. Two Separable e licitor-responsive elements were found to reside between -99 and -87 and be tween -87 and -37. These two elements are not redundant in the Tdc promoter , since their combination gave a distinct elicitor response.