Novel insights into the action of SHI/STY transcriptional regulators during plant development

Sammanfattning: One key player in plant organogenesis is the phytohormone auxin, and this thesis reveal that members of the SHI/STY gene family participate in the regulation of auxin homeostasis and organ development in Arabidopsis thaliana. Using inducible constructs, ChIP, and EMSA, we could show that the SHI/STY members act as transcriptional activators directly binding to the promoter of the auxin biosynthesis gene YUC4. Additional putative downstream targets were identified encoding transcription factors, other auxin biosynthesis enzymes and enzymes involved in cell wall modulations. This work also brings novel insight into SHI/STY-dependent regulation of cotyledon and leaf vascular patterning and stamen number. Detailed expression studies of SHI/STY genes and several downstream targets confirm their overlapping spatial and temporal expression pattern during cotyledon, leaf, stamen and gynoecium development, clearly supporting the partially redundant function of the SHI/STY family members during the development of these organs. In addition, the expression of SHI/STY members is partially mediated through a conserved motif in their promoter region, a GCC-box, which appears to be essential for SHI/STY expression in aerial organs. Furthermore, a group of putative upstream regulators belonging to the AP2/ERF family have been identified, which requires the GCC-box for their transcriptional regulation of the SHI/STY genes.