Synergistic control of auxin mediated transcription by ARF and C/S1 bZIP transcription factors

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In order to sustain optimal plant growth, auxin regulated transcription is adjusted according to environ-mental signals. This project studies the integration of signals into auxin-mediated transcriptional pat-terns. Using the Arabidopsis GH3.3 promoter as a model, we could demonstrate that AUXIN RESPONSE ELEMENTS (AuxREs), G-BOX RELATED ELEMENTS (GREs) and MYB RESPONSIVE ELEMENTS (MREs) cooperate in auxin-mediated transcription. Whereas AUXIN RESPONSE FACTORS (ARFs) mediate auxin-responsiveness via AuxREs, GREs and MREs act as quantitative elements. This project focuses on the impact of the group S1 basic leucine zipper (bZIP) transcription factors AtbZIP2, AtbZIP11 and AtbZIP44 which modulate auxin responses via binding to GREs. Estra-diol-induced gain- and loss-of function approaches in transgenic plants will be used to study the impact of these bZIPs on auxin-regulated transcription and its in vivo binding to the respective promoters. De-pending on bZIP expression, typical auxin responses such as initiation of lateral roots, root hair forma-tion and gravitropic responses will be studied. As C/S1 bZIP network modulates primary metabolism in response to energy stress, we postulate that the GRE/bZIP module functions as a “rheostate” which provides means to balance auxin-mediated growth responses with the energy status of the cell.