Strigolactone (and/or derived molecules) signalling pathways in land plants – StrigoPath

Molecular biology (transcriptomics) and organic synthesis are used in the project to have a better understanding of SL signalling pathways in the two systems. Bioactive profluorescent SLs (fluorescence is released after hydrolysis of the probe by the receptor) are synthesized. They allow the characterization of the enzymatic activity of the receptor which belongs to the super-family of a,ß-hydrolase. Gene function is analyzed using reverse genetic (TILLING in pea, homologous recombination and CRISPR-CAS9 thechnology in moss and by biochemical studies.

A novel mechanism of SL reception by the a,ß-hydrolase has been proposed based on the use of the profluorescent probes. Enzymatic characteristics of SL receptors have been defined.
SL signaling pathways are different between the moss and vascular plants: analysis of the Ppmax2 moss mutant indicates that the function of the MAX2 gene is preceded by its role in photomorphogenesis. In moss, several D14like genes (instead of one D14 and 2 D14like in pea) are candidates for encoding the SL receptor.

Tilling mutants obtained in pea for genes responding to SLs will lead to a better understanding of SL signaling for branching inhibition and internode elongation. Single and multiple moss mutants for the D14like genes will be analysed to investigate whether they are affected in SL response. Profluorescent probes will permit to characterize the enzymatic activity for different substrates of the potential SL receptors in moss

de Saint Germain et al. (2013) Novel insights into strigolactone distribution and signalling Curr. Opin. Plant Biol. 16: 583-589

Boyer et al. (2014) New Strigolactone Analogues as Plant Hormones with Low Activities in the Rhizosphere. Molecular Plant: (2014) 7: 675-690

Brevet N° de dépôt FR 12 54700. Nouveaux analogues de SLs et leur utilisation pour le Traitement des Plantes. BOYER, F.-D. ; RAMEAU, C. ; PILLOT, J.-P. ; SERVAJEAN, V. ; DE SAINT GERMAIN, A. ; BEAU, J.-M. Extension internationale : 23 mai 2013. PCT/EP2013/060624

Hoffmann B, Proust H, Belcram K, Labrune C, Boyer FD, Rameau C, Bonhomme S. (2014) Strigolactones Inhibit Caulonema Elongation and Cell Division in the Moss Physcomitrella patens. PLoS One.;9(6):e99206.

Boyer F-D, de Saint Germain A, Pouvreau J-B, Clavé G, Pillot J-P, Roux A, Rasmussen A, Depuydt S, Lauressergues D, Frei dit Frey N, Heugebaert TSA, Stevens CV, Geelen D, Goormachtig S, Rameau C (2014) New Strigolactone Analogs as Plant Hormones with Low Activities in the Rhizosphere. Molecular Plant 7: 675-690

Strigolactones are the most recent discovered class of plant hormones, carotenoid-derived, that have been shown to repress shoot branching. They are mainly produced in roots and were previously known to act in the rhizosphere as signaling the presence of the host root to parasitic plants (Striga, Orobanche) and to arbuscular mycorrhizal fungi. Their triple action as inducers of parasitic plant seed germination and of hyphal proliferation, and as inhibitors of lateral branching in plants, is a remarkable and intriguing plant signalling story. The recent discovery that strigolactones stimulate cambium activity indicates that they can induce cell proliferation in their hormonal activity. To date, more than 13 natural strigolactones have been identified in root exudates of land plants. The structural core of the strigolactones is a tricyclic lactone (ABC part) connected via an enol ether bridge to an a/ß-unsaturated furanone moiety (D ring). The structural diversity of strigolactones within and between species raises questions about possible differential activities of those molecules in their hormonal functions, in parasitic weed germination and hyphal branching. It is very likely that this class of compounds is very ancient as the arbuscular mycorrhizal symbiosis evolved for 460 million years before the appearance of roots and the moss Physcomitrella patens has been shown to produce strigolactones. In this non-vascular plant, opposite effects of strigolactones on moss protonema (filaments) development have also been observed according environmental conditions. This project aims to decipher the strigolactone signaling pathway(s) and to understand its evolution among land plants by combining two approaches, transcriptomics (RNA seq) and Structure-Activity Relationship studies in two systems: a vascular plant, Pisum sativum, and a non-vascular plant P. patens. Tritiated labeled-strigolactones will be synthesized and used in metabolism studies to identify putative bioactive SL-derived compounds and/or deactivation products. During this project, the bioactive SL or SL-derived compounds and the molecular components of the signaling pathway will be compared between the different systems under study: pea axillary buds and node/stem, protonema filaments of moss in light and dark conditions. Reverse genetics (TILLING in pea, homologous recombination in moss) and binding studies between ligands and putative receptors will further characterized the function of genes. This work will create knowledge on a new plant growth hormone that affects a diverse number of plant properties. These important traits include shoot number, fruit size, water and nutrient uptake, wood production. It will allow us to design strategies for plant improvement and management and for controlling particular potentially devastating parasitic weeds.