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Structure, fonction et évolution de LEAFY, facteur de transcription clé du développement floral

Abstract : LEAFY (LFY) is a key transcription factor for plant development, particularly for flowering in angiosperms. LFY is highly conserved in plants, including non-flowering species. Despite a wealth of genetic data about LFY and its regulatory network in the model plant Arabidopsis thaliana, how the protein works at the molecular level is not fully understood. It has two conserved domains: a DNA binding domain and a N-terminal domain of unknown function. My two main projects were to understand the role of the N-terminal domain and to study LFY DNA binding specificity evolution. We obtained LFY N-terminal domain crystal structure and discovered it was a Sterile-Alpha-Motif (SAM) mediating LFY oligomerisation. We validated the importance of that property for flower development in A. thaliana. Using both in vitro analyses and a ChIP-seq experiment, we pointed out that oligomerisation is required for proper DNA binding. It enables cooperative binding on several LFY binding sites, increases the protein selectivity towards DNA and allows LFY to access genomic regions where the chromatin conformation normally prevents binding. This integrative study provides a better understanding of how LFY works. The rewiring of transcriptional networks provides a rich source of evolutionary novelty. As LFY is highly conserved and single copy in most plant genomes, we asked whether its DNA binding specificity had evolved. We showed that LFY was present since multicellular algae and that it underwent at least two major shifts in DNA-binding specificity during plant evolution. We provided a structural explanation for the two newly identified DNA binding modes and we identified a LFY form with a relaxed specificity that could have served as an intermediate between evolutionary transitions.
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Camille Sayou. Structure, fonction et évolution de LEAFY, facteur de transcription clé du développement floral. Sciences agricoles. Université Grenoble Alpes, 2013. Français. ⟨NNT : 2013GRENV029⟩. ⟨tel-01222909⟩

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