TCP1 Modulates DWF4 Expression via Directly Interacting with the GGNCCC Motifs in the Promoter Region of DWF4 in Arabidopsis thaliana

Our previous studies indicated that TCP1 is a positive regulator of the brassinosteroid (BR) biosynthesis pathway by mediating the transcription of DWF4, one of the key BR biosynthetic genes in Arabidopsis thaliana. Whether TCP1 can directly bind to the promoter region of DWF4, however, has not been experimentally demonstrated. Here we provide our biochemical and genetic evidence that TCP1 mediates the expression of DWF4 by directly associating with the two GGNCCC motifs in the promoter region of DWF4. The expression levels of DWF4 are positively correlated to TCP1 abundance in planta. Electrophoretic mobility shift assays (EMSAs) using various synthetic DNA fragments suggest that the GGNCCC core sequence is critical for TCP1 binding. DNA sequences flanking the GGNCCC motifs are less important for the association of TCP1. Using DWF4p-GUS transgenic plants as an assay system, it is clearly indicated that these motifs are required for the positive regulation of DWF4 transcription by TCP1. More significantly, whole genome microarray analyses indicate that TCP1 can directly or indirectly regulate the expression of many other genes known to be important for normal plant growth and development.