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Hicham Chahtane

Functional and evolutionary study of LEAFY, a key transcription factor in flower development

Published on 3 October 2014

Thesis presented October 03, 2014

Abstract :
Flower formation comprises three successive steps. First, a new meristem, containing stem cells, is formed on the flank of the inflorescence meristem. Then, this meristem adopts a floral identity. Finally, floral morphogenesis occurs that allow the development of floral organs arranged into four distinct whorls. The LEAFY (LFY) transcription factor is a major regulator of floral development in flowering plants. The aim of my thesis was to precisely understand the roles of LFY during floral development, especially during early stages. Previous studies in the model plant A. thaliana demonstrate that LFY can multimerize upon binding to DNA. By studying the functional importance of the dimerization property of LFY, we were able to show that this property is important for the regulation of its target genes, including those responsible for floral identity. In addition, by combining genetic studies, transcriptomic data​ as well as whole-genome LFY binding sites, we have shown that LFY controls a new network of genes which are directly involved in meristem formation, before its determination into flower. These data raise the prospect that this new function of LFY is in fact a non-floral function already present in most land plants.
LFY is highly conserved in all land plants, but is not part of a multigene family in contrast to most transcription factors. I studied the evolution of LFY properties, including its ability to dimerize on specific DNA sequences. For this purpose, we looked for the ancestor form of LFY and found out that LFY was already present in multicellular green algae. By studying the dimerization interface in different counterparts of LFY, we demonstrate that the acquisition of this dimerization property has played a crucial role during the evolution of the protein.
Finally, I studied the post-translational control of LFY activity which remains largely unknown. Preliminary results are presented and suggest that this mode of regulation is important for many functions of this orphan transcription factor.

LEAFY, meristem, stem cells, flower, transcription factor, dimerization, evolution