LEAFY, a plant transcription factor as a model for transcriptional activation by ubiquitination

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Flowers are the most complex structure of flowering plants or angiosperms. Flowers ensure successful reproduction of angiosperms and are the basis for fruit and seed development, which are major food source for humans and animals. The plant-specific transcription factor LEAFY (LFY) is the master regulator of flower development in angiosperms. LFY specifies the emergence of the floral meristem identity and therefore, plays a central role in the developmental switch from vegetative stage (leaves and branches) to reproductive stage (flowers). Recently it has been shown that LFY activity is dependent on the interaction with the F-box protein UNUSUAL FLORAL ORGANS (UFO). UFO is an ubiquitin ligase and it is assumed that UFO is involved in protein degradation. It is known that LFY can trigger the formation of flowers from leaves in conjunction with UFO, but how UFO potentiates LFY activity has remained obscure. Although few examples of transcriptional activation by ubiquitination and possible degradation of transcription factors exist in yeast and mammals, this mechanism has so far not been ascribed to plants. The aim of this project is to unravel the biological role of LFY-UFO interaction in flower development and what the role of ubiquitination pathways is in regard of LFY activity as a test case for activation of transcription by ubiquitination in plants. I plan to investigate the mechanism of the LFY-UFO interaction in conjunction with the ubiquitin-system and to analyse the molecular consequences on target gene expression and flower development using an integrated approach using cell biology, biochemistry, molecular biology, top-notch imaging and proteomics. LFY is the perfect model to investigate this fundamental question in biology, due to its well-known characteristics and functions (structure, DNA binding properties, interacting partners, target genes, etc), as well as available tools. The knowledge gained from my studies will clearly benefit to the understanding of flower development in plants, especially since the LFY-UFO interactions was identified in several flowering plants. Besides, this project will tackle a question of general significance in biology regarding how ubiquitination can activate transcription, therefore being of great interest to communities interested in transcription and ubiquitination in other model organisms.