Transactivation properties of parsley proline‐rich bZIP transcription factors

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Abstract
Light‐responsive chalcone synthase (CHS) gene activation requires LRUCHS, a light regulatory promoter unit including the MYB recognition element MRECHS and the ACGT‐containing element ACECHS. ACECHS is bound by the parsley basic region/leucine zipper (bZIP) factors CPRF1 and 4. Factors containing the bZIP domain exist in animals, plants and yeast, and recognize DNA sequence‐specifically after formation of homo‐ or heterodimers. To determine the potential role of CPRFs in the regulation of CHS promoter activity, we investigated the functions of distinct CPRF domains in a homologous co‐transfection system. The proline‐rich domains of CPRF1 and CPRF4 activate transcription, indicating that CPRF1 and CPRF4 have transactivating properties. Over‐expression of the CPRF1 bZIP domain caused a reduction of LRUCHS‐mediated light inducibility, and point mutations throughout ACECHS affected both responsiveness to UV‐containing white light and transactivation by CPRF1::VP16. The data suggest that a CPRF1‐containing bZIP heterodimer interacts with ACECHSin vivo. We discuss regulatory steps in light‐induced CHS transcription that may be influenced by CPRF1 and/or related bZIP factors.