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Edwige Moyroud

Changing role and biochemical properties of a central regulator of the LEAFY floral development

Published on 6 October 2010

Thesis presented October 06, 2010

Flowers are a key innovation in plant evolution and their origin remains a mystery. LEAFY (LFY) is a unique plant transcription factor regulating f​loral development, but this gene predates flowers. My thesis work aimed to understand how the evolution of LFY biochemical properties could help explaining flower origins.
First, I took part in the structural characterization of LFY DNA-binding domain, revealing a novel protein fold bound to DNA as a cooperative dimer (Hamès et al., 2009). To exhaustively characterize its DNA binding specificity, I set up a SELEX experiment that yielded hundreds of sequences with high-affinity for LFY. Based on these sequences, I built a LFY binding site predictive model (position weight matrix) that I validated in vitro. This matrix led to a biophysical model, able to explain the set of genomic regions bound by LFY in vivo, as established in a ChIP-seq experiment in Arabidopsis seedlings, but also to detect functional orthologues​ of LFY targets genes in other angiosperms genomes.
Since LFY is present in mosses, ferns and gymnosperms that do not flower, I tested if its DNA binding specificity is different in these groups. In parallel, I uncovered correlations between the expression patterns of LFY genes and several homologs of floral homeotic genes in the gymnosperm, Welwitschia mirabilis. After demonstrating that surface plasmon resonance can be used to analyze interactions between transcription factors and entire gene promoters (Moyroud et al., 2009), I tested the interplay between LFY and its potential targets in Welwitschia and established that a pre-floral network was already at work in non-flowering plants.

Arabidopsis thaliana, Welwitschia mirabilis, LEAFY, transcription factor, SELEX, ChIP-seq, floral development

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