The soils of Martinique and Guadeloupe are contaminated by chlordecone (CLD), an organochlorine pesticide used in the French West Indies until 1993 to control the banana weevil. Despite a cessation of use for almost 30 years, soil still represents a continuous source of CLD that can be transferred to other environmental compartments such as surface and groundwater. This impact on ecosystems has environmental but also health consequences. Reducing soil contamination by CLD is therefore a major challenge in order to reduce exposure and, consequently, reduce the impacts on health and the environment. The objective of DéMETer is to implement an efficient, economically viable, operational and acceptable method for soil treatment with regard to CLD and its degradation products. If there are several promising remediation solutions, such as those combining chemical reduction and phytoremediation, their operational implementation requires resolving technical and societal obstacles. These are the objectives of DéMETer: 1) optimize remediation processes regarding both efficiency and cost, 2) ensure that these remediation processes are socially acceptable and acquired by the stakeholders, and 3) validate the change of scale by implementing demonstrators on site and evaluating the technical and economic constraints for their eventual implementation on a very large scale. The later (obj 4) also includes ensuring the transferability of this integrated approach to similar contexts, i.e., Guadeloupe. To achieve these objectives, DéMETer, which relies on a transdisciplinary consortium, answers the challenges of axis 1 (prevention of exposure) and axis 2 (Science and society) of the call for projects and responds to several expected outcomes of the Chlordecone IV plan.

GRaSP (Genetics of Rhizobia Selection by Pea) is a collaborative research project that proposes an original approach to improve the pea-Rhizobium beneficial interaction by mobilizing a multidisciplinary complementary expertise of four different academic French partners together with a private partner involved in the promotion of grain legume cultivation in France. Legumes, because of their ability to form a beneficial symbiotic interaction with nitrogen-fixing Rhizobium bacteria, are projected to play an increasingly important role in sustainable agriculture. Moreover, legumes are a valuable source of protein for both feed and food, but are not grown as extensively as would be expected in France and Europe due to variability in yield and protein content. For these reasons genomic approaches are being developed to improve several important agronomic traits essential to develop higher and more stable yielding varieties in major legume crops such as pea. However, to date little attention has been paid to improving the interaction with its symbiotic partner, especially when the symbiotic partner is a mix of different Rlv strains. Establishment of the symbiosis involves mutual recognition of the plant and rhizobia partners in the soil, followed by the development of root symbiotic organs called nodules. The symbiotic interaction between pea and rhizobia is specific to strains of Rhizobium leguminosarum sv. viciae (Rlv). Past research has pointed out the role of early pea-Rlv signaling events in partner selection, but a broad understanding of the genetic determinants that govern partner choice and competitiveness for nodulation between Rlv strains in mixture is lacking. In the GRaSP project, two complementary strategies are proposed to improve this knowledge. The first one will decipher the genetic architecture of the complex trait of pea-Rlv partner choice and identify specific loci that underlie this phenotype though a Genome Wide Association Study. In parallel, the second strategy will investigate the role of variation of several pea and Rlv genes that control the specificity of symbiosis, i.e. recognition by the plant of symbiotic signals produced by rhizobia. Both approaches will benefit from large pea and Rlv collections, increasing genomic resources and high-throughput phenotyping abilities that are available among the four academic partners of the consortium. A proof-of concept of the selection for improved pea-Rhizobium associations identified in the two different approaches will be tested through the expertise of the private partner in different field conditions where data for their Rlv native population diversity are already available. GRaSP will lead to predictive understanding of pea-Rlv partner choice and knowledge-based molecular strategies which will be useful to breed peas for improved nodulation in fields with highly competitive and efficient rhizobial inocula.

Legumes play a major agronomical and ecological role due to their ability to fix atmospheric nitrogen during symbiosis with rhizobia. The main legume crops are tropical species (soybean, peanut, mungbean, …) that represent more than 85% of the grain legume production. These species are all nodulated by Bradyrhizobium strains which contain nodulation genes (nod genes) necessary for the synthesis of key symbiotic signals, named Nod factors (NFs), but also T3SS genes that encode the Type 3 Secretion System. This secretory machinery, initially identified in animal and plant bacterial pathogens, permits the delivery of effector proteins inside the host cells where they interfere with various host processes including suppression of immune responses and favour the infection. For a long time, it was assumed that nodulation absolutely required NFs to trigger nodule organogenesis and infection. The T3SS machinery on the other hand was viewed as an accessory equipment, which modulates the efficiency and the host spectrum of the bacteria. However, it has been shown that some legume species of the Aeschynomene genus but also the cultivar Glycine max cv. Enrie are nodulated by Bradyrhizobium strains even if NF synthesis is disrupted. In this case, the establishment of the interaction requires that the bacteria has a functional T3SS indicating that specific Type 3 effectors can directly activate the nodulation signalling pathway in legumes, bypassing the perception of NFs. Recently, we have demonstrated that in the Bradyrhizobium strain ORS3257 this T3SS-dependent symbiosis relies on a cocktail of at least five effectors playing synergistic and complementary roles in nodule organogenesis, infection and repression of plant immune responses. Among them, we identified the nuclear-targeted ErnA effector, which is highly conserved among bradyrhizobia, as a key actor for nodule organogenesis. Furthermore, preliminary data indicate that other Bradyrhizobium strains can use other Type 3 effectors, distinct of ErnA, to trigger nodulation in legumes. Our discovery that a single effector protein is sufficient to induce nodule organogenesis without the need of NFs is a paradigm shift in the field and indicates that legume nodulation programs are not exclusively controlled by NFs. Our main goals in the current ET-Nod project are: i) to decipher the molecular mechanisms by which ErnA activates nodulation in Aeschynomene, ii) to identify new effectors (named ET-Nods) behaving like ErnA in the triggering of nodulation and iii) to characterize the importance of this effector family in the symbiotic efficiency of agronomically important legumes. For these purposes, our consortium, involving specialists in plant symbiosis and pathogenesis will i) combine biochemical, genetic and omic approaches to characterize the molecular target(s) and interactome of ErnA, ii) develop at the level of the Bradyrhizobium genus a comparative genomic analysis coupled with a mutagenesis approach to identify new ET-Nod effectors and iii) investigate, using bacterial and plant genetics, the role played by ErnA and ET-Nod effectors in various Bradyrhizobium strains during symbioses with legume crops (soybean, peanut, cowpea …). The knowledge acquired during this project could be exploited in agronomy to improve yield of several legume crops and to design new strategies aimed at transferring nitrogen-fixing symbiosis to cereals.

Plants benefit from two major symbiotic interactions with soil microbes, the Arbuscular Mycorrhizal (AM) and the Rhizobium-Legume (RL) symbioses, to improve their mineral nutrition. They generally establish such associations following recognition of symbiotic chitin-derived molecules called Myc-LCOs and Nod factors (NFs) when they are produced by AM fungi and rhizobia, respectively. These symbiotic signal molecules are perceived by members of the plant LysM-domain Receptor-Like Kinase (LysM-RLK) family, which also controls the perception of pathogenic chitinic molecules. In the model legume Medicago truncatula, we have shown that four LysM-RLK receptors are particularly important for symbiosis and/or immunity; MtNFP, MtLYK3, MtLYR3 and MtLYK9. We have also shown the presence of these four LysM-RLKs in Aeschynomene evenia, which is an exception in legumes in not requiring NFs for the RL symbiosis. How specific signal recognition through LysM-RLKs leads to the distinction of symbionts from pathogens, and what might be their functions in a NF-independent context is not well understood. Upon perception of symbiotic signals or pathogenic elicitors the regulation of Reactive Oxygen Species (ROS) and nitrogen species homeostasis, including hydrogen peroxide and nitric oxide (NO), constitutes one of the earliest known plant responses. In M. truncatula, symbiotic signals induce a rapid change in ROS and can block a pathogen-induced ROS burst, both effects being dependent on MtNFP. This supports close connections between MtNFP and ROS regulation for symbiosis and immunity. We have also shown that ROS and NO can have positive roles in both the AM and the RL symbioses, and that in A. evenia, ROS production and cell collapse are early steps of NF-independent symbiosis. We hypothesise that (i) the fine-tuned spatio-temporal dynamics of ROS and NO production via LysM receptors is a critical component of the mechanisms that enable M. truncatula to distinguish between symbiotic and pathogenic signals, (ii) LysM-RLK and ROS/NO have different roles in the establishment of the NF-independent RL symbiosis in A. evenia. The originality of the DUALITY project is to study LysM-RLK receptors and redox state that both have crucial, and closely linked, roles in symbiosis and immunity. Our objectives are to determine (1) the precise “signatures” of ROS and NO production in different biotic conditions, as well as in both NF-dependent and NF-independent nodulation; (2) the roles of key LysM-RLKs in the regulation of redox signalling; (3) the variations to LysM-RLKs and their roles in influencing redox control to enable NF-independent nodulation; and (4) how MtNFP controls interactions with contrasting outcomes. To tackle these aims, DUALITY brings together 4 partners who are leaders in the fields of LysM receptors and symbiotic signalling in M. truncatula (P1), redox signalling (P2), plant immunity (P3) and Nod factor-independent symbiosis in A. evenia (P4). The project will exploit innovative new tools such as biosensors for in vivo spatio-temporal analysis of redox states; recently obtained genetic and genomic resources for A. evenia; new M. truncatula plant mutants (in receptors and redox signalling), and new MtNFP interacting proteins. This work is anticipated to provide breakthroughs to explain the mechanisms by which some members of an important family of plant receptors largely involved in plant-microbe interactions, transmit microbial signalling via changes in redox balance that control defence to pathogens and symbiosis establishment. In turn, such knowledge may provide leads to simultaneously maintain efficient symbiosis and increase disease resistance in order to promote sustainable agriculture.

The FAO estimates a 34% increase in the world population by 2050. As a result, the productivity of important staple crops such as cereals and horticultural species needs to be boosted by an estimated 43%. Against the mosaic global climate change and shifting arable land ranges, plant and soil sciences play a primordial role in finding solutions to the internationally shared challenges of ensuring sustainable agricultural and biomass production. However, to effectively meet these challenges and demands, knowledge obtained from essential plant and soil sciences must be connected to innovative applications in agriculture and plant cultivation. Hence, sustainable biological practices such as biofertilizers (compost and microorganisms) that boost plant yield, quality or even novel functionality, and tolerance to abiotic stresses should be exploited to improve agricultural production. For this purpose, this project addresses all aspects of the global food system by being good for the consumer, good for the planet and good for the farmer. By combining the complementary expertise of different research teams and companies from Morocco, France, Germany, Turkey, Tunisia, Algeria, Japan, and Mexico, we aim at (i) developing cultivation technologies verified and demonstrated in the field to tackle some challenges simultaneously, including food insecurity, malnutrition and other diet-related health issues, rural poverty, and mitigation of climate change, (ii) exploitation of beneficial indigenous microorganisms biofertilizers and agents to achieve sustainable and highly productive agriculture, and to mitigate climate change, (iii) recycling of green and agro-industrial waste into compost and biostimulants that can be reused in agriculture allowing the improvement of the soil fertility/functioning and crops yield, and (iv) understanding of the phenotypes and molecular traits of leading staple food crops (cereals and horticultural crops) under diverse environmental conditions.