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Arnaud Stigliani

Modeling DNA binding and function of key floral transcription factors

Published on 2 October 2019
Thesis presented October 02, 2019

In angiosperms, the development of flowers takes place in several stages. The meristem, a stem cell reservoir from which all the plant’s aerial organs emerge, first differentiate into an inflorescence meristem. Floral meristems then emerge from the flanks of the inflorescence meristem to give birth to the different organs that compose the flower: the petals, sepals, stamens and carpel. Each of these phases is finely regulated by transcription factors, a family of proteins that bind to DNA to induce gene activation or repression. If this thesis allowed us to contribute to the JASPAR database, which gather transcription factor binding profiles, its main goal is to provide a new perspective on the understanding of the phenomena that control flower development through the study of a handful of key transcription factors in the regulation of floral development. We have tried to explain the parameters that influence the binding of these transcription factors using bioinformatics models associated with genomics experiments.
We have analysed the auxin response factors (ARF) through the study of two representatives of this family of 23 proteins: ARF2 and ARF5. The transcription factors of this family are known to bind in dimers and we have shown that ARF2 and ARF5 prefer different spacings between monomeric binding sites on DNA. We have also shown that some configurations seem to favour the activation of bound genes.
Then, we have studied LFY, a master transcription factor of floral development. We have improved an existing binding model and have seen that the integration of genomic data of various kinds provides a better understanding of the binding of the transcription factor in vivo.
Finally, we have analyzed the preferences of MADS box transcription factors, known to bind the same DNA sequences and whose role is to determine the identity of floral organs. Through the study of the SEP3/AG complex, which controls the formation of the carpel, we have found that the tetramerization domain of these factors confers binding specificity, potentially explaining that groups of MADS box transcription factors regulate the formation of different floral organs by activating distinct genes.

Transcription factor, Gene regulation, flower development, Bioinformatics

On-line thesis.