StrigoPath

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.