Structure-Function of AG-like MADS in Gymnosperms

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Janeau, Aline | Zubieta, Chloé | Hugouvieux, Véronique | Lucas, Jérémy | Parcy, François

Edité par CCSD -

International audience. The last key stage in plant evolution lead to the appearance of flowers in which both reproductive organs (stamens and carpels) are co-localised and protected by sterile organs (petals and sepals) in Angiosperms. In this novel structure, the main morphological changes were observed for the female organ, from nude ovules in Gymnosperms to the carpel protecting the ovule in flowering plants. This new structure increased the efficiency of fertilization and seed dispersal, likely leading to the present-day diversity and domination of terrestrial ecosystems by flowering plants. Despite this morphological evolution, at the molecular level, female reproductive organ development in Gymnosperms appears to be regulated by the same key factor: C-class MADS box transcription factors. The mechanism controlling carpel identity has been well studied in Angiosperms, and involves tetrameric heterocomplexes formed by two MADS proteins, SEPALLATA (SEP; E-class) and AGAMOUS (AG; C-class). SEP proteins are key factors for tetramer formation in Angiosperms, MADS floral organ identity tetramers do not form without a SEP protein and tetramer formation is required for gene expression regulation. In Gymnosperms, no SEP homologs have been identified, however, AG homologs have been identified and showed homotetramerisation capacity in vitro. However, detailed investigation of the molecular mechanisms of action of AG homologues in Gymnosperms is not available. Using an integrated structural approach from the atomic to the organism level, I am investigating the structure-function of AG-like MADS complexes from Gymnosperms. Homologs from two different species are used: GNETUM GNEMON MADS 3 (GGM3) from Gnetum gnemon and CYCAS AGAMOUS (CyAG) from Cycas edentate. I will present my recent findings, that combine in vitro and in vivo experiments, from structural and DNA binding properties analysis, to functional and protein transcriptional activity analysis of this complexes.

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