Berns, Markus Christian (2012) Transcriptional regulation of the Arabidopsis thaliana flowering-time gene GIGANTEA. PhD thesis, Universität zu Köln.
Plants adjust their developmental programmes to the surrounding environment, which allows them to colonise almost every habitat on earth. One key player in regulating different developmental processes in response to the environment in Arabidopsis thaliana is GIGANTEA (GI), a circadian-clock regulated protein that is most abundant in the evening. The precise timing of GI transcription is proposed to be crucial for it to fulfil its different functions such as the regulation of flowering time, raising the question of how GI itself is transcriptionally regulated. A combination of phylogenetic and genome-wide bioinformatic analysis as well as the study of transgenic promoter-reporter and complementation lines demonstrated that a highly conserved 700bp block within the GI promoter is important for many aspects of GI regulation and function. These include the response to light and temperature, control of hypocotyl growth and the regulation of flowering time. Moreover, conserved Evening Element (EE) motifs within this block were shown to be important for several specific features of GI transcription. Having shown the importance of EEs within the GI promoter, all EEs were mapped on a genome-wide level and co-occurrences with other circadian-clock related cis-regulatory elements were determined. This analysis revealed striking patterns between EEs and between other cis-elements that gave insights into the general transcriptional code in plants. Taken together, this thesis demonstrates that the pleiotropic functions of GI in light signalling, the circadian clock, freezing tolerance and the regulation of flowering time are reflected within its promoter. This work not only contributed to understanding the complex transcriptional regulation of GI and its function in the plant, but also provided novel insights into the regulation of co-expressed genes and the general transcriptional code in plants.
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