The G-box and H-box in a 39 bp region of a French bean chalcone synthase promoter constitute a tissue-specific regulatory element

Two adjacent motifs, the G-box and H-box, in the bean chalcone synthase (CHS) gene promoter are essential for floral and root specific expression. To evaluate the cooperative role of these motifs as a tissue-specific regulatory element, a synthetic 39 bp DNA fragment containing the two motifs was prepared. Polymers of this fragment were linked to minimal CHS15 promoter, or cauliflower mosaic virus 35S promoter, and fused to the beta-D-glucuronidase (GUS) reporter gene. Measurements of GUS activity in transformed tobacco plants revealed that the 39 bp polymer confers upon both minimal promoters a high level of expression that follows the typical tissue-specific expression pattern. Mutations in either the G-box or H-box motifs abolished expression, emphasizing the essential role of each motif in transcriptional activation. These results define an exclusive and cooperative element in the CHS15 promoter which contains the information necessary to establish the typical CHS15 tissue-specific expression pattern. However, this element is present within the context of the native promoter, and it requires additional cis-elements to modulate the level and temporal expression established during plant development.