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

The tryptophan decarboxylase (Tdc) gene from Catharanthus roseus (Madagascar periwinkle) encodes a key enzyme in biosynthesis of terpenoid indole alkaloids. The expression of the Tdc gene is transcriptionally induced by fungal elicitors. Tdc upstream sequences from -1818 to +198 relative to the transcriptional start site were functionally analysed to identify cis-acting elements 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. Whereas 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 truncated promoters. Combination of the data resulted in the identification of three functional regions in the -160 promoter. The region between -160 to -99 was shown to act as the main transcriptional enhancer. Two separable elicitor-responsive elements were found to reside between -99 and -87 and between -87 and -37. These two elements are not redundant in the Tdc promoter, since their combination gave a distinct elicitor response.