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Marie Monniaux

Evolution of the floral regulator LEAFY in land plants.

Published on 11 December 2012

Thesis presented December 11, 2012

LEAFY (LFY) is a unique transcription factor, highly conserved within land plants. LFY directly regulates a set of genes participating in floral development in angiosperms (flowering plants), but its role in the other groups of land plants is unknown, except in the moss Physcomitrella patens where the LFY orthologous (PpLFY) regulates the first cell division in the zygote. PpLFY does not bind to the same DNA sequences as LFY from Arabidopsis thaliana, in spite of the very h​igh degree of conservation of their DNA binding domains. Thus, it appears that the properties of LFY have changed during evolution; the goal of my thesis was to find out if such changes had occurred frequently in land plants, and what are their origins and consequences on target genes regulation.
I performed SELEX experiments on LFY orthologues from all land plants, which revealed that their DNA binding specificity was highly conserved, except in the case of PpLFY. These results allowed us to build an accurate biophysical model to predict LFY binding on DNA fragments at a genomic level, which we applied on the evolution of the regulation of key target genes by LFY. We were able to predict the regulation of the floral gene AGAMOUS by LFY in various angiosperm species, et we could also show that LFY was very likely regulating gymnosperm orthologues of genes involved in floral organ identity, even before the appearance of the flower.
The change in DNA binding specificity observed for PpLFY led us to study more precisely the consequences of this change for the regulation of target genes: for this, I initiated bioinformatics​ and experimental work in P. patens. Finally, to understand how this change in DNA binding specificity had occurred during evolution, we are currently investigation the ancestral specificity of LFY in land plants.

LEAFY, floral development, transcription factor, evolution, DNA binding specificity, Arabidopsis thaliana, Physcomitrella patens

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