Pascal Ratet

• Dr.
• Research Director at French National Centre for Scientific Research

The emergence of commensalism and mutualism often derives from ancestral parasitism. However, in the case of rhizobium-legume interactions, bacterial strains displaying both pathogenic and nodulation features on a single host have not been described yet. Here, we isolated such a bacterium from Medicago nodules. On the same plant genotypes, the T4 s...

The establishment of symbiotic interactions between leguminous plants and rhizobia requires complex cellular programming activated by Rhizobium Nod factors (NFs) as well as type III effector (T3E)-mediated symbiotic signaling. However, the mechanisms by which different signals jointly affect symbiosis are still unclear. Here we describe the mechani...

Mitigating pre-harvest sprouting (PHS) and post-harvest food loss (PHFL) is essential for enhancing food securrity. To reduce food loss, the use of plant derived specialized metabolites can represent a good approach to develop a more eco-friendly agriculture. Here, we have discovered that soybean seeds hidden underground during winter by Tscherskia...

Immunity and senescence play a crucial role in the functioning of the legume symbiotic nodules. The miss-regulation of one of these processes compromises the symbiosis leading to death of the endosymbiont and the arrest of the nodule functioning. The relationship between immunity and senescence has been extensively studied in plant organs where a s...

Losses due to disease and climate change are among the most important issues currently facing crop production. It is therefore important to establish the impact of climate change, and particularly of high carbon dioxide (hCO2), on plant immunity in cereals, which provide 60% of human calories. The aim of this study was to determine if hCO2 impacts...

Wheat is one of the most important crops in the world. Its production can be influenced by a diversity of beneficial and pathogenic rhizospheric microbes, including fungi. Amongst them, beneficial Trichoderma spp. can be used as alternatives to chemical fertilizers, as they are cheap and harmless to the environment. Our study aimed to isolate, iden...

Soybean is a pivotal staple crop worldwide, supplying the main food and feed plant proteins in some countries. In addition to interacting with mutualistic microbes, soybean also needs to protect itself against pathogens. However, to grow inside plant tissues, plant defense mechanisms ranging from passive barriers to induced defense reactions have t...

LEAFY plant-specific transcription factors, which are key regulators of flower meristem identity and floral patterning, also contribute to meristem activity. Notably, in some legumes, LFY orthologs such as Medicago truncatula SINGLE LEAFLET (SGL1) are essential in maintaining an undifferentiated and proliferating fate required for leaflet formation...

Medicago (Medicago truncatula) establishes a symbiosis with the rhizobia Sinorhizobium sp, resulting in the formation of nodules where the bacteria fix atmospheric nitrogen. Loss of immunity repression or early senescence activation compromises symbiont survival and leads to the formation of non-functional nodules (fix-). Despite many studies explo...

Medicago truncatula NODULE ROOT1 (MtNOOT1) and Pisum sativum COCHLEATA1 (PsCOCH1) are orthologous genes belonging to the NOOT-BOP-COCH-LIKE (NBCL) gene family which encodes key transcriptional co-regulators of plant development. In Mtnoot1 and Pscoch1 mutants, the development of stipule, flower and symbiotic nodules is altered. MtNOOT2 and PsCOCH2...

13th International Conference of the French Society of Plant Biology August 29 ‐ 31 2022; Montpellier ‐ France

The Multi-Trait selection index (MTSI) has been used to select highly productive and stable faba bean landraces across various traits. Fifteen productive, morphological, and phenological traits with desired and undesired selection gains (SGs) were evaluated in fifteen faba bean landraces under Mediterranean field conditions between 2019–2021. Accor...

Most major crops are polyploid species and the production of genetically engineered cultivars normally requires the introgression of transgenic or gene-edited traits into elite germplasm. Thus, a main goal of plant research is the search of systems to identify dominant mutations. In this article, we show that the Tnt1 element can be used to identif...

In cultivated grasses, tillering, leaf and inflorescence architecture, as well as abscission ability, are major agronomical traits. In barley (Hordeum vulgare), maize (Zea mays), rice (Oryza sativa), and brachypodium (Brachypodium distachyon), NOOT-BOP-COCH-LIKE (NBCL) genes are essential regulators of vegetative and reproductive development. Grass...

In the environment microbes interact with plants and provide them with benefits that include protection against biotic and abiotic stresses as well as improved nutrition. However, plants are also exposed to parasites and pathogens. To manage appropriate responses, evolution has resulted in improved tolerance of plants to beneficial microbes while k...

The induction of plant somatic embryogenesis is often a limiting step for plant multiplication and genetic manipulation in numerous crops. It depends on multiple signaling developmental processes involving phytohormones and the induction of specific genes. The WUSCHEL gene (WUS) is required for the production of plant embryogenic stem cells. To exp...

In cultivated grasses, tillering, spike architecture and seed shattering represent major agronomical traits. In barley, maize and rice, the NOOT‐BOP‐COCH‐LIKE (NBCL) genes play important roles in development, especially in ligule development, tillering and flower identity. However, compared with dicots, the role of grass NBCL genes is underinvestig...

Legumes have the capacity to develop root nodules hosting nitrogen-fixing bacteria, called rhizobia. For the plant, the benefit of the symbiosis is important in nitrogen-deprived conditions, but it requires hosting and feeding massive numbers of rhizobia. Recent studies suggest that innate immunity is reduced or suppressed within nodules [1-10]; th...

Some plants can engage symbiosis with nitrogen !xing soil bacteria, allowing them to grow when soils are poor in nitrogen. This symbiotic association results in the formation of a unique plant root organ called the nodule. In these nodules, bacteria can convert atmospheric dinitrogen into ammonia that can be used by the plant. Establishment of a su...

Some plants can engage symbiosis with nitrogen fixing soil bacteria, allowing them to grow when soils are poor in nitrogen. This symbiotic association results in the formation of a unique plant root organ called the nodule. In these nodules, bacteria can convert atmospheric dinitrogen into ammonia that can be used by the plant. Establishment of a s...

Maillet et al., 2019, Supplementary Figures as single file

Some plants are able to grow in nitrogen-poor soils because they can establish symbiosis with rhizobia or frankia (actinobacteria) bacteria, which are able to reduce the non-limiting atmospheric gaseous nitrogen (N2) to NH3 to the benefit of their host. The capacity to establish this symbiosis, also called root nodule symbiosis (RNS), is confined t...

The formation of nitrogen‐fixing nodules on legume hosts is a finely tuned process involving many components of both symbiotic partners. Production of the exopolysaccharide succinoglycan by the nitrogen‐fixing bacterium Sinorhizobium meliloti 1021 is needed for an effective symbiosis with Medicago spp., and the succinyl modification to this polysac...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Rhodophiala bifida (R. bifida) is a representative of the Amaryllidaceae plant family and is rich in montanine, an alkaloid with high pharmaceutical potential. Despite the interest in these compounds, many steps of the biosynthetic pathway have not been elucidated. In this study, we identified the alkaloids produced in different organs of R. bifida...

Objectives The aim of this study was to develop a Trifolium pratense hairy root (HR) production protocol and select HR lines with high isoflavone yield following elicitor treatments. Results We obtained 13 independent HR lines, producing approximately three times more isoflavonoids than seedlings (3.3 mg/g dry weight) and in which 27 isoflavonoids...

Plants of the legume family host massive intracellular bacterial populations in the tissues of specialized organs: the nodules. In these organs, the bacteria, named rhizobia, can fix atmospheric nitrogen and transfer it to the plant. This special metabolic skill provides to the legumes an advantage when they grow on nitrogen scarce substrates. Whil...

Medicago truncatula is able to perform a symbiotic association with Sinorhizobium spp. This interaction leads to the formation of a new root organ, the nodule, in which bacteria infect the host cells and fix atmospheric nitrogen for the plant benefit. Multiple and complex processes are essential for the success of this interaction from the recognit...

Symbiotic interactions between legume plants and rhizobia result in the formation of nitrogen-fixing nodules, but the molecular actors and the mechanisms allowing for the maintenance of nodule identity are poorly understood. Medicago truncatula NODULE ROOT1 (MtNOOT1), Pisum sativum COCHLEATA1 (PsCOCH1) and Lotus japonicus NOOT-BOP-COCH-LIKE1 (LjNBC...

Massive intracellular populations of symbiotic bacteria, referred to as rhizobia, are housed in legume root nodules. Little is known about the mechanisms preventing the development of defense in these organs although genes such as Sym CRK and DNF 2 of the model legume Medicago truncatula are required for this control after rhizobial internalization...

The NOOT‐BOP‐COCH‐LIKE (NBCL) genes are orthologs of Arabidopsis thaliana BLADE‐ON‐PETIOLE1/2. NBCLs are developmental regulators essential for plant shaping mainly through the regulation of organ boundaries, the promotion of lateral organ differentiation and the acquisition of organ identity. In addition to their roles in leaf, stipule and flower...

Legumes form endosymbiotic interaction with host compatible rhizobia, resulting in the development of nitrogen-fixing root nodules. Within symbiotic nodules, rhizobia are intracellularly accommodated in plant-derived membrane compartments, termed symbiosomes. In mature nodule, the massively colonized cells tolerate the existence of rhizobia without...

Medicago truncatula was chosen by the legume community, along with Lotus japonicus, as a model plant to study legume biology. Since then, numerous resources and tools have been developed for M. truncatula. These include, for example, its genome sequence, core ecotype collections, transformation/regeneration methods, extensive mutant collections, an...

Strain CCMM B554, also known as FSM-MA, is a soil dwelling and nodule forming, nitrogen-fixing bacterium isolated from the nodules of the legume Medicago arborea L. in the Maamora Forest, Morocco. The strain forms effective nitrogen fixing nodules on species of the Medicago, Melilotus and Trigonella genera and is exceptional because it is a highly...

Maize roots can be colonized by free-living atmospheric nitrogen (N2)-fixing bacteria (diazotrophs). However, the agronomic potential of non-symbiotic N2-fixation in such an economically important species as maize, has still not been fully exploited. A preliminary approach to improve our understanding of the mechanisms controlling the establishment...

Figure A. Experimental gnotobiotic systems for axenic inoculation of maize plantlets with the bacterial N2-fixing endophytes Herbaspririllum seropedicae and Azospririllum brasilense. (a) System used for bacterial counting and metabolomic analyses. 7d = seven days after inoculation, 14d = fourteen days after inoculation. (b) System used for measurin...

Aeschynomene evenia has emerged as a new model legume for the deciphering of the molecular mechanisms of an alternative symbiotic process that is independent of the Nod factors. Whereas most of the research on nitrogen-fixing symbiosis, legume genetics and genomics has so far focused on Galegoid and Phaseolid legumes, A. evenia falls in the more ba...

The Tnt1 retrotransposon of tobacco (Nicotiana tabacum) has proven to be a very efficient mutagen for the model legume Medicago truncatula ecotype 108 and cultivar Jemalong 2HA and for economically important plants, such as soybean and potato. In this study, the activity of Tnt1 in the model legume Lotus japonicus L. was tested. First, a new regene...

The majority of angiosperms are syncarpous- their gynoecium is composed of two or more fused carpels. In Arabidopsis thaliana, this fusion is regulated through the balance of expression between CUP SHAPED COTYLEDON (CUC) genes, which are orthologs of the Petunia hybrida transcription factor NO APICAL MERISTEM (NAM), and their post-transcriptional r...

Plants are able to lose organs selectively through a process called abscission. This process relies on the differentiation of specialized territories at the junction between organs and the plant body that are called abscission zones ( AZ ). Several genes control the formation or functioning of these AZ . We have characterized BLADE ‐ ON ‐ PETIOLE (...

Microbes are phylogenetically (Archaea, Bacteria, Eukarya, and viruses) and functionally diverse. They colonize highly varied environments and rapidly respond to and evolve as a response to local and global environmental changes, including those induced by pollutants resulting from human activities. This review exemplifies the Microbial Ecology EC2...

Legume plants develop symbiosis-specific organs on their root, called nodules, which house nitrogen-fixing bacteria. The molecular mechanisms governing the identity and maintenance of these organs are still unknown. The Medicago truncatula nodule root (noot) and pea cochleata (coch) mutants are characterized by the development of roots from the nod...

Legumes are special among cultivated plants because they establish symbiotic associations with nitrogen-fixing bacteria. Being able to grow well in nitrogen-poor soils, they play a vital role in sustainable crop production. Understanding the functions and roles of genes and proteins involved in legume–rhizobia symbiosis is of great importance not o...

Microbes are phylogenetically (Archaea, Bacteria, Eukarya, and viruses) and functionally diverse. They colonize highly varied environments and rapidly respond to and evolve as a response to local and global environmental changes, including those induced by pollutants resulting from human activities. This review exemplifies the Microbial Ecology EC2...

Medicago truncatula belongs to the legume family and forms symbiotic associations with nitrogen fixing bacteria, the rhizobia. During these interactions, the plants develop root nodules in which bacteria invade the plant cells and fix nitrogen for the benefit of the plant. Despite massive infection, legume nodules do not develop visible defence rea...

Legumes have been for a long time recalcitrant to efficient Agrobacterium transformation. The choice and use of model legume plants (Medicago truncatula and Lotus japonicus) for molecular studies has triggered extensive studies devoted to the development of efficient Agrobacterium-mediated transformation protocols for these two plants. In M. trunca...

New research results have significantly revised our understanding of the rhizobium-legume infection process. For example, Nod factors (NFs), previously thought to be absolutely essential for this symbiosis, were shown to be dispensable under particular conditions. Similarly, an NF receptor, previously considered to be solely involved in symbiosis,...

Lignocellulosic biomass has the potential to be a significant source of renewable energy, provided that current challenges regarding sufficient biomass production and efficient biomass conversion are met. Floral transition is a major developmental switch in the life of flowering plants which dictates whether photosynthetic products should be invest...

The Medicago truncatula WOX gene, STENOFOLIA (STF), and its orthologs in Petunia, pea, and Nicotiana sylvestris are required for leaf blade outgrowth and floral organ development as demonstrated by severe phenotypes in single mutants. But the Arabidopsis wox1 mutant displays a narrow leaf phenotype only when combined with the prs/wox3 mutant. In ma...

Strigolactones were recently identified as a new class of plant hormones involved in the control of shoot branching. The characterization of strigolactone mutants in several species has progressively revealed their contribution to several other aspects of development in roots and shoots. In this article, we characterize strigolactone-deficient and...

Author Summary Despite the essential functions of roots in plant access to water and nutrients, root system architecture has not been directly considered for crop breeding improvement, but it is now considered key for a “second green revolution.” In this study, we aimed to decipher integrated molecular mechanisms coordinating lateral organ developm...

Background Legumes form root nodules to house nitrogen fixing bacteria of the rhizobium family. The rhizobia are located intracellularly in the symbiotic nodule cells. In the legume Medicago truncatula these cells produce high amounts of Nodule-specific Cysteine-Rich (NCR) peptides which induce differentiation of the rhizobia into enlarged, polyplo...

To investigate how exudation shapes root-associated bacterial populations, transgenic Arabidopsis thaliana plants that exuded the xenotopic compound octopine at low and high rates were grown in a non-sterile soil. Enumerations of both cultivable and octopine-degrading bacteria demonstrated that the ratios of octopine degraders increased along with...

Rhizobia and legumes establish symbiotic interactions leading to the production of root nodules, in which bacteria fix atmospheric nitrogen for the plant's benefit. This symbiosis is efficient because of the high rhizobia population within nodules. Here, we investigated how legumes accommodate such bacterial colonization. We used a reverse genetic...

Most plant species form symbioses with arbuscular mycorrhizal (AM) fungi, which facilitate the uptake of mineral nutrients such as phosphate from the soil. Several transporters, particularly proton-coupled phosphate transporters, have been identified on both the plant and fungal membranes and contribute to delivering phosphate from fungi to plants....

Rhizobia and legumes are able to interact in a symbiotic way leading to the development of root nodules. Within nodules, rhizobia fix nitrogen for the benefit of the plant. These interactions are efficient because spectacularly high densities of nitrogen fixing rhizobia are maintained in the plant cells. DNF2, a Medicago truncatula gene has been de...

M edicago truncatula is one of the model species for legume studies. In an effort to develop legume genetics resources, > 21 700 T nt1 retrotransposon insertion lines have been generated. To facilitate fast‐growing needs in functional genomics, two reverse genetics approaches have been established: web‐based database searching and PCR ‐based revers...

Legume plants are important in agriculture because they represent an important source of protein for human and animal consumption. This high protein content results from their capacity to use atmospheric nitrogen for their nutrition as a consequence of their symbiotic interaction with rhizobia. Understanding this interaction at the molecular level...

Molecular-genetic control of the flowering time of temperate-climate plants is best understood in Arabidopsis and the cereals wheat and barley. However, key regulators such as FLC and cereal VRN2 are not found in legumes. Therefore, we used forward genetics to identify flowering time genes in the model legume Medicago truncatula (Medicago) which is...

A large population of Medicago truncatula insertion lines has been generated using the Tnt1 retrotransposon. More than 21,000 insertion lines have been generated, representing more than 500,000 insertion events. This mutant population is being used by the legume research community to screen for various different mutants using a forward genetics app...

Legume plants develop symbiosis specific organs on their roots as a result of their interaction with rhizobia. These organs, called nodules, house the nitrogen fixing bacteria. The molecular mechanisms governing the identity and maintenance of this organ are still poorly understood, but it is supposed that root and nodule development share common f...

[FeFe]-hydrogenase-like genes encode [Fe4 S4 ] containing proteins that are ubiquitous in eukaryotic cells. In human, IOP1 represses HIF1-α at normal atmospheric partial O2 pressure (normoxia, 21 kPa O2 ). In yeast, the nar1 mutant cannot grow at 21kPa O2, but can develop at lower O2 pressure (2kPa O2 ). We show here that plant [FeFe]-hydrogenase-l...

Medicago truncatula and Sinorhizobium meliloti form a symbiotic association resulting in the formation of nitrogen-fixing nodules. In this organ, symbiotic cells contain large numbers of bacteroids. Remarkably, this chronic infection does not trigger visible defense reactions. Despite the importance of this phenomenon for potential transfer of the...

In recent years numerous genetic resources have been developed for the model legume Medicago truncatula, including Tnt1-insertion and fast-neutron deletion mutant populations, the Gene Expression Atlas (MtGEA), and the largely complete genome sequence. Transcriptomic studies revealed that thousands of plant genes are involved in SNF; however, a sma...

To extend our understanding of flowering time control in eudicots, we screened for mutants in the model legume Medicago truncatula (Medicago). We identified an early flowering mutant, spring1, in a T-DNA mutant screen, but spring1 was not tagged and was deemed a somaclonal mutant. We backcrossed the mutant to wild type R108. The F1 plants and the m...

Genotyping shows segregation distortion of a DNA marker in the spring1 interval in F2 plants of the cross of “spring1 x Jester”. PCR genotyping using a DNA marker (FTa1) from the interval containing spring1 was carried out on plant DNA samples from the two mapping crosses. These included the early and late flowering plants, but also additional samp...

Microarray identification of genes that are differentially expressed in leaves of spring1 compared to R108. The log fold change in gene expression with a p value of ≤0.05 was calculated from 3 biological repeats of each genotype grown in long day conditions. The first trifoliate leaf at the three-leaf stage was harvested. Each biological replicate...

List of annotated genes predicted within the ∼0.5 Mb interval containing spring1. The gene annotations were obtained from the BAC sequences in Medicago pseudomolecule Mt3.5 genome assembly http://medicagohapmap.org/. The three FT genes are in BAC AC123593 and shown in bold. (DOCX)

The DNA sequence of R108 and spring1 is identical in the FTa1 genomic region, but differs from the reference genome A17. a) Diagram showing the predicted gene annotation in the spring1 mapping interval in the vicinity of the three FT genes. b) Diagram comparing the DNA sequences of the FTa1 region between R108 and A17. PCR was used to amplify the r...

Legume plants are used as a protein source for human and animal nutrition. The high protein content of legume plants is achieved via the establishment of a root symbiosis with rhizobia that allows the reduction of atmospheric nitrogen. In recent years, M. truncatula has been used as a legume model in view of its small, diploid genome, self-fertilit...

Medicago truncatula and Sinorhizobium meliloti form a symbiotic association resulting in the formation of nitrogen‐fixing nodules. Nodule cells contain large numbers of bacteroids which are differentiated, nitrogen‐fixing forms of the symbiotic bacteria. In the nodules, symbiotic plant cells home and maintain hundreds of viable bacteria. In order t...

During their symbiotic interaction with rhizobia, legume plants develop symbiosis-specific organs on their roots, called nodules, that house nitrogen-fixing bacteria. The molecular mechanisms governing the identity and maintenance of these organs are unknown. Using Medicago truncatula nodule root (noot) mutants and pea (Pisum sativum) cochleata (co...

Legumes establish mutualistic associations with mycorrhizal fungi and with nitrogen-fixing rhizobial bacteria. These interactions occur following plant recognition of Nod factor from rhizobial bacteria and Myc factor from mycorrhizal fungi [1-3]. A common symbiosis signaling pathway is involved in the recognition of both Nod factor and Myc factor a...

A Tnt1-insertion mutant population of Medicago truncatula ecotype R108 was screened for defects in nodulation and symbiotic nitrogen fixation. Primary screening of 9,300 mutant lines yielded 317 lines with putative defects in nodule development and/or nitrogen fixation. Of these, 230 lines were rescreened, and 156 lines were confirmed with defectiv...

To identify genes that confer nonhost resistance to biotrophic fungal pathogens, we did a forward-genetics screen using Medicago truncatula Tnt1 retrotransposon insertion lines. From this screen, we identified an inhibitor of rust germ tube differentation1 (irg1) mutant that failed to promote preinfection structure differentiation of two rust patho...