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Two signaling pathways of butenolide compounds, strigolactones (SLs) and karrikins (KARs), have been recently discovered in plants. SLs are a class of plant hormone involved in repressing shoot branching and having a role in both parasitic and symbiotic interactions in the rhizosphere. KARs, found in fire smoke, can stimulate seed germination and seedling development. SLs and KARs act through similar signaling pathways and share the F-box protein MORE AXILLARY GROWTH2 (MAX2) and receptors of the same alpha/beta-hydrolase subfamily, DWARF14 (D14) for SLs and KARRIKIN INSENSITIVE2 (KAI2) for KARs. KAI2 is the ancestral form and it has been suggested that it could be the receptor of an endogenous ligand, a potential novel plant hormone. In collaboration with François-Didier Boyer (ICSN, Gif sur Yvette), who developed fluorescent probes, we found a novel mechanism of hormone reception not described previously. We showed that the catalytic activity of the SL receptor leads to a receptor/product complex necessary for recruiting partners of the SL signaling pathway. Today, I would like to come back in the group of Catherine Rameau in order to bring my expertise in biochemistry. This project aims two major goals: first I would like to elaborate a strategy to determine the endogenous substrate(s) of the KAI2 receptor based on an in vitro rapid chemical library screening using profluorescent probes. Second, I want to compare SL and KAR perception in different plant models already used in Rameau’s lab: Physcomitrella patens (used for evolutionary studies), tomato (an important agronomical plant where repressing shoot branching would be a good application) and parasitic plants. During my post-doc, I obtained several tools (constructs) that I could use for the project. Moreover, I gained expertise in biochemical methods (enzymatic assay, binding assay and mass spectrometry, and crystallization). I will use these skills for a better understanding of the different mechanisms of perception involved.
My research is focused on plant architecture signaling and more precisely on strigolactone perception, a phytohormone involved in the control of shoot branching. My overall strategy, both during my PhD completed in 2012 at the Institut Jean-Pierre Bourgin (IJPB) of INRA-Versailles and during my first postdoc at the SALK Institute in San Diego (USA), has been to: (i) Identify genes involved in the strigolactone perception by forward and reverse genetic approaches, (ii) Elucidate the perception mechanism of strigolactone by the RMS3 protein using biochemical approach (iii) Look for crosstalk between strigolactone and the other classical developmental hormones as gibberellin and auxin. Using genetic, biochemistry and chemistry, in the model plant Arabidopsis thaliana and the crop Pisum sativum, I have been able to pinpoint a new paradigm in plant hormone perception in which the receptor acts as an enzyme to generate its own substrate and induce signaling transduction. During my AgreenSkills fellowship in IJPB lab, my research focused on the study of strigolactone perception evolution in land plant by characterizing the SL receptor homologues in the bryophyte model Physcomitrella patens and the parasitic plant Phelipanche ramosa.
Ligerot Y, de Saint Germain A, Waldie T, Troadec C, Citerne S, Kadakia N, Pillot JP, Prigge M, Aubert G, Bendahmane A, Leyser O, Estelle M, Debellé F, Rameau C., 2017. The pea branching RMS2 gene encodes the PsAFB4/5 auxin receptor and is involved in an auxin-strigolactone regulation loop. PLoS Genet. 8;13(12):e1007089. Doi: 10.1371/journal. pgen.1007089.
de Saint Germain A, Guillaume Clavé, Marie Ange BadetDenisot, Jean-Paul Pillot, Jean-Pierre Lecaer, Frank Pelissier, Pascal Retailleau, Jean-Bernard Pouvreau, Virginie Puech, Colin Turnbull, Sandrine Bonhomme, Joanne Chory, Catherine Rameau and François-Didier Boyer, 2016. An histidine covalent receptor/butenolide complex is involved in strigolactone perception. Nat Chem Biol. 12 (10), 787-794.
de Saint Germain A, Ligerot Y, Dun EA, Pillot JP, Ross JJ, Beveridge CA, Rameau C., 2013. Strigolactones stimulate internode length independently of gibberellins. Plant Physiol., 163(2):1012-1025.
de Saint Germain A, Bonhomme S, Boyer FD, Rameau C. Novel insights into strigolactone distribution and signalling. Curr Opin Plant Biol. 16(5):583-589. Doi: 10.1016/j.pbi.2013.06.007.
Braun N, de Saint Germain A, Pillot JP, Boutet-Mercey S, Dalmais M, Antoniadi I, Li X, Maia-Grondard A, Le Signor C, Bouteiller N, Luo D, Bendahmane A, Turnbull C, Rameau C., 2012. The pea TCP transcription factor PsBRC1 acts downstream of Strigolactones to control shoot branching. Plant Physiol. 158(1):225-38.
Boyer F.-D., Rameau C, Pillot J-P, De Saint-Germain A, Pouvreau J.-B. Nouveaux analogues de strigolactones spécifiquement actif sur le contrôle de la ramification des plantes agissant faiblement sur la germination des plantes parasites de type Orobanche. Patent number : FR 11 58917