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Cécile Hames

Structural and functional study of the Arabidopsis thaliana LEAFY floral regulator

Published on 26 September 2008

Thesis presented September 26, 2008

LEAFY (LFY) protein is a key regulator of floral development. Its gradually increased expression governs the sharp floral transition and LFY subsequently controls the patterning of flower meristems by inducing the expression of the floral homeotic genes APETALA1 (AP1), APETALA3 (AP3) and AGAMOUS (AG). According to some theories of evolution, LFY should have also played a central role in the appearance of flowering plants (Angiosperms). Despite a wealth of genetic data, how LFY functions at the molecular level is poorly understood. LFY is the only member of a transcription factor family specific of plant kingdom and its primary sequence looks like no other. The most important breakthrough of my PhD work, the obtention of the 3-D structure of LFY C-terminal domain (LFY-C) from Arabidopsis thaliana bound to two of its target genes, AP1 and AG, now helps us to better understand how this original protein works. LFY-C adopts a novel seven-helix fold and forms base- specific contacts in both the major and the minor grooves of DNA. LFY-C binds DNA as a cooperative dimer mediated by two basic residues. This cooperativity could partly explain LFY’s effectiveness in triggering sharp flowering transition. The structure reveals also an unexpected similarity between LFY and HTH proteins such as homeodomain transcription factors or paired protein involve in animal development. Finally, allowing us to study LFY orthologues from all terrestrial plants in a novel way, these data provide a unique framework to elucidate the molecular mechanisms underlying the evolutionary history of flowering plants.

Floral development, Angiosperms, LFY, LFY-C, Arabidopsis thaliana, flowering transition, homeodomain transcription factors

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