Abstact

DNA-binding with one-finger (Dof) proteins are a family of plant-specific transcription factors distinguished by the highly conserved Dof DNA-binding domain. Various members play crucial roles in diverse plant biological processes. However, it remains unclear how the Dof domain recognizes a restricted set of promoters for gene regulation by binding to just four nucleotides, AAAG/CTTT. Here we present the crystal structure of the Dof domain of CYCLING DOF FACTOR 1 (CDF1), a well-characterized Dof protein acting as a transcriptional repressor by binding to the CONSTANS promoter to regulate photoperiodic flowering, in complex with DNA containing two cis elements. The data reveal that the Dof domain exhibits a unique zinc ribbon fold that includes a three-stranded antiparallel β-sheet and a carboxy-terminal loop, enabling DNA recognition accompanied by directional expansion of the major groove. These features facilitate binding to contiguous target cis elements in a proper arrangement to effectively regulate gene expression.