Abstract
How distinct cell fates are specified at correct positions within the plant embryo is unknown. To address mechanisms of position-dependent gene activation and cell fate specification, we analyzed the regulatory region of the ATML1 gene, which is already expressed at the one-cell stage and whose expression is later restricted to the outermost, epidermal, cell layer from its inception. A sensitive multiple GFP reporter revealed a modular organization of the ATML1 promoter. Each region contributes to specific spatial and temporal aspects of the overall expression pattern, including position-dependent regulation along the apical-basal axis of the embryo. A 101-bp fragment that conferred all aspects of ATML1 expression contained known binding sites for homeodomain transcription factors and other regulatory sequences. Our results suggest that expression patterns associated with cell fate determination in the plant embryo result from positional signals targeting different regulatory sequences in complex promoters.
