Strigolactones and Allelochemicals Signaling

  Identification of genes and specialized metabolites involved in allelopathy (Alexandre de Saint Germain, Sophie Jasinski)

Our agriculture is facing the challenge of agro-ecological transition, with the need to progressively reduce the use of herbicides. The development of innovative strategies for tomorrow's agriculture could come from new knowledge on the natural mechanisms of regulation of plant-plant interactions, such as allelopathy. This process by which plants release chemical compounds into the rhizosphere, molecules that modify the growth of neighbouring plants, appears to be an interesting lever for promoting the biological regulation of weeds. To date, few allelopathic compounds have been identified and our knowledge of the molecular mechanisms involved is limited, partly due to methodological constraints. The SAS team is developing projects combining genetic and metabolomic approaches to identify the genes and metabolites involved in allelopathy. Using an innovative phenotyping device for allelopathic properties and association genomics studies (GWAS), it has been possible to identify candidate genes potentially involved in the biosynthesis of allelopathic signals in the model plant Arabidopsis.

  Mechanism of strigolactone perception (Alexandre de Saint Germain, François-Didier Boyer)

Strigolactones are perceived by terrestrial plants as a plant hormone, by parasitic plants of the Orobanchaceae family (genus Striga, Orobanche, Phelipanche) as a germination stimulant and by arbuscular endomycorrhizal fungi. The strigolactone receptor in vascular plants (D14 in rice, RMS3 in pea) is a member of the large family of α/β-hydrolases. These proteins are therefore both receptors and enzymes. In 2016, the team sought to better understand the role of this enzymatic activity in the SL perception mechanism. Our results revealed a novel mechanism of hormone reception whereby the receptor performs an irreversible enzymatic reaction to generate its own ligand. The team is currently interested in strigolactone receptors (and other germination stimulants) in the sunflower parasitic plant, Orobanche cumana. In these obligate parasitic plants, a diversification of KAI2 proteins, the homologs of the D14 receptor, is observed (as in the moss, see below).  

Strigolactones are very ancient and diverse molecules. A recent study on the bryophyte Marchantia paleacea suggests that in the first land plants, strigolactones did not have a hormonal role but rather a role in the rhizosphere, particularly for the establishment of symbiosis with mycorrhizal fungi. In the model bryophyte used in the laboratory, the moss Physcomitrium patens, strigolactones appear to have a hormonal and/or allelopathic role as they are exuded by plants and regulate plant extension. The team has identified strigolactone receptors in mosses and is currently working for a better understanding of the evolution of the signalling pathways of these molecules, which certainly participated in the colonisation of the terrestrial environment by plants more than 450 million years ago. In the framework of the MALCOM-X ANR project (2022-2026), the team aims to identify the structure of allelopathic molecules in Physcomitrium patens.  

In 2008, strigolactones became a novel class of plant hormones for their role in the control of shoot branching, a discovery in which the team was involved. The team will not pursue this theme after the current thesis on the characterisation of genes of the biosynthesis pathway in pea. One of the questions currently being asked is the identification of strigolactones that inhibit branching in pea. Each species produces a mixture of different strigolactones. The thesis focuses on the downstream genes in the biosynthetic pathway that are involved in the diversification of strigolactones. Mutants for these genes, which are deficient in certain pea strigolactones, do not show the classic hyper-branching phenotype, suggesting that these (so-called canonical) strigolactones do not have a hormonal role but rather a role in the rhizosphere.