Diversity and Evolution of the Phenazine Biosynthesis Pathway

ABSTRACT Phenazines are versatile secondary metabolites of bacterial origin that function in biological control of plant pathogens and contribute to the ecological fitness and pathogenicity of the producing strains. In this study, we employed a collection of 94 strains having various geographic, environmental, and clinical origins to study the distribution and evolution of phenazine genes in members of the genera Pseudomonas , Burkholderia , Pectobacterium , Brevibacterium , and Streptomyces . Our results confirmed the diversity of phenazine producers and revealed that most of them appear to be soil-dwelling and/or plant-associated species. Genome analyses and comparisons of phylogenies inf…

Nodulating symbiotic bacteria and soil quality

Chapitre 9 : Plant microbe interactions and soil quality Partie : 9-2; International audience

Biologie des communautés dans la rhizosphère : analyse des interactions plantes - champignons mycorhizogènes à arbuscules - bactéries

National audience

Impact of Bacterial Siderophores on Iron Status and Ionome in Pea

National audience; Including more grain legumes in cropping systems is important for the development of agroecological practices and the diversification of protein sources for human and animal consumption. Grain legume yield and quality is impacted by abiotic stresses resulting from fluctuating availabilities in essential nutrients such as iron deficiency chlorosis (IDC). Promoting plant iron nutrition could mitigate IDC that currently impedes legume cultivation in calcareous soils, and increase the iron content of legume seeds and its bioavailability. There is growing evidence that plant microbiota contribute to plant iron nutrition and might account for variations in the sensitivity of pe…

Importance de la diversité microbienne dans les interactions entre microorganismes et hôtes eucaryotes

Interactions between Pisum sativum & pseudomonads, consequences on plant iron nutrition and growth and immunity

Pea has a high potential in agroecology, however, it may suffer from a susceptibility to iron deficiency in calcareous soils. This susceptibility varies depending on cultivars. Pseudomonad siderophores, pyoverdines (pvd), were shown to promote iron nutrition in Arabidopsis and tobacco. The hypothesis was therefore raised that variation in iron susceptibility between pea cultivars could be related to differences in their ability to recruit fluorescent pseudomonads (fp) contributing to siderophore-mediated iron nutrition. Our aims were to compare i) the impact of a susceptible (S) and a tolerant (T) cultivar of pea on fp biodiversity with a focus on their pvd, and in return ii) the impact of …

Strategies for analyzing interactions between arbuscular mycorrhiza and bacteria

National audience

Analysis of the role of nitric oxide (NO) in the cross‐regulation between immunity, growth and iron homeostasis in plants

Studies performed in our Agroecology Department show that the immune response of plants is linked to their iron nutrition and is modulated by pyoverdine, a siderophore produced by the plant beneficial rhizobacteria Pseudomonas fluorescens C7R12. Accordingly, Arabidopsis thaliana plantlets exposed to iron deficiency and treated with pyoverdine in its iron non‐chelated structure (apo‐pyo) show an enhanced growth but a decreased immune response capacity. We hypothesize that nitric oxide (NO), a universal signaling molecule, is a key component of the regulation of the immune response in plants exposed to apo‐pyo and to the C7R12 strain. We checked by fluorescence microscopy that NO is actually …

Reciprocal interactions between plants and fluorescent pseudomonads in relation to iron in the rhizosphere

SPE EA Section 15 : Engineering the rhizosphere: The "biased rhizosphere" concept Ouvrage en 2 volumes Résumé du livre : Molecular Microbial Ecology of the Rhizosphere covers current knowledge on the molecular basis of plant-microbe interactions in the rhizosphere. Also included in the book are both reviews and research-based chapters describing experimental materials and methods. Edited by a leader in the field, with contributions from authors around the world, Molecular Microbial Ecology of the Rhizosphere brings together the most up-to-date research in this expanding area, and will be a valuable resource for molecular microbiologists and plant soil scientists, as well as upper level stud…

Medicago species affect the community composition of arbuscular mycorrhizal fungi associated with roots

National audience; The symbiosis between plants and arbuscular mycorrhizal fungi (AMF) is ancient and involves 80% of terrestrial plant families. The symbiotic association between AMF and plants was described to be non specific. However, AMF were reported to influence plant community diversity and productivity. On the other way, the effect of plant genotypes belonging to closely related species on AMF diversity has not been explored so far. The aim of this work was to assess the impact of four different Medicago species, M. laciniata, M. murex, M. polymorpha and M. truncatula cv. Jemalong J5, on the composition of AM fungal community, when cultivated in a silty-thin clay soil (Mas d’Imbert,…

Interactions plantes/micro-organismes dans la rhizosphère

Prod 2018-76e EA SPE BIOME INRA AGROSUP; National audience; Chapitre 4. Interactions plantes/micro-organismes dans la rhizosphère La rhizosphère, un lieu d’échanges multiplesRecrutement des micro-organismes dans la rhizosphèreInteractions plantes/micro-organismes, une longue histoireMicrobiote rhizosphérique, des bénéfices pour la planteValorisation des interactions plantes/micro-organismes en agroécologieConclusion et perspectives Bibliographie résumé du livre : Les sols sont des milieux où évolue une myriade d’organismes différents, déterminant une série de fonctions, qui se traduisent en services écosystémiques essentiels pour l’humanité. Mieux connaitre ces organismes, leur biodiversité…

Distribution and diversity of type III secretion system-like genes in saprophytic and phytopathogenic fluorescent pseudomonads

Type three secretion systems (TTSSs) are protein translocation mechanisms associated with bacterial pathogenicity in host plants, and hypersensitive reactions in non-host plants. Distribution and diversity of TTSS-like genes within a collection of saprophytic and phytopathogenic fluorescent pseudomonads were characterized. This collection included 16 strains belonging to 13 pathogenic species, and 87 strains belonging to five saprophytic species isolated from plant rhizosphere and soil. Presence of conserved hypersensitive reaction/pathogenicity (hrp) genes (hrc RST) was assessed both by PCR using primers designed to amplify the corresponding sequence and by dot-blot hybridization using a P…

Influence of pea genotype on root associated fluorescent pseudomonads, impact on plant iron nutrition

International audience; Pea has a high potential in agroecology because of its ability to fix atmospheric nitrogen and for Humannutrition due to the high amino-acids content of its seeds. However, pea can suffer from a susceptibility toiron deficiency in calcareous soils as expressed by chlorosis symptoms. Previous studies have shown thatsiderophores of model strains of fluorescent pseudomonads (fp), pyoverdines, promote iron nutrition ofarabidopsis and tobacco. We hypothesized that susceptibility to iron deficiency of pea is at least partly dueto its ability to select fluorescent pseudomonad that promote differentially plant nutrition thanks to theirsiderophores.To identify siderophores po…

Knowledge tranfer from fundamental research to practical application in biological nitrogen fixation : prospects and reality

International audience

Fluorescent pseudomonads harboring type III secretion genes are enriched in the mycorrhizosphere of Medicago truncatula

Type III secretion systems (T3SSs) of Gram-negative bacteria mediate direct interactions with eukaryotic cells. Pseudomonas spp. harboring T3SS genes (T3SS+) were previously shown to be more abundant in the rhizosphere than in bulk soil. To discriminate the contribution of roots and associated arbuscular mycorrhizal fungi (AMF) on the enrichment of T3SS+ fluorescent pseudomonads in the rhizosphere of Medicago truncatula, their frequency was assessed among pseudomonads isolated from mycorrhizal and nonmycorrhizal roots and from bulk soil. T3SS genes were identified by PCR targeting a conserved hrcRST DNA fragment. Polymorphism of hrcRST in T3SS+ isolates was assessed by PCR-restriction fragm…

Contribution of fluorescent pseudomonads to iron nutrition and health of pea

Identification de microorganismes, gènes et activités microbiennes impliqués dans les interactions plantes-microorganismes : conséquences pour la croissance et la santé des plantes

Microdiversity of Burkholderiales associated with mycorrhizal and nonmycorrhizal roots of Medicago truncatula

The genetic diversity of bacterial communities associated with mycorrhizal and nonmycorrhizal roots of Medicago truncatula was characterized by two approaches. Firstly, phylogenetic analysis was performed on 164 partial 16S rRNA gene-intergenic spacer (IGS) sequences from operational taxonomic units previously shown to be preferentially associated with mycorrhizal roots. These sequences were distributed into three branches corresponding to Comamonadaceae, Oxalobacteraceae and Rubrivivax subgroups. Most sequences were obtained from mycorrhizal roots, indicating the preferential association of the corresponding families with mycorrhizal roots. A second phylogenetic analysis was performed on t…

Fitness in soil and rhizosphere of Pseudomonas fluorescens C7R12 compared with a C7R12 mutant affected in pyoverdine synthesis and uptake.

International audience; Fluorescent pseudomonads have evolved an efficient strategy of iron uptake based on the synthesis of the siderophore pyoverdine and its relevant outer membrane receptor. The possible implication of pyoverdine synthesis and uptake on the ecological competence of a model strain (Pseudomonas fluorescens C7R12) in soil habitats was evaluated using a pyoverdine minus mutant (PL1) obtained by random insertion of the transposon Tn5. The Tn5 flanking DNA was amplified by inverse PCR and sequenced. The nucleotide sequence was found to show a high level of identity with pvsB, a pyoverdine synthetase. As expected, the mutant PL1 was significantly more susceptible to iron starva…

The Pseudomonas fluorescens Siderophore Pyoverdine Weakens Arabidopsis thaliana Defense in Favor of Growth in Iron-Deficient Conditions

SPE EA BIOME IPM UB INRA; International audience; Pyoverdines are siderophores synthesized by fluorescent Pseudomonas spp. Under iron-limiting conditions, these high-affinity ferric iron chelators are excreted by bacteria in the soil to acquire iron. Pyoverdines produced by beneficial Pseudomonas spp. ameliorate plant growth. Here, we investigate the physiological incidence and mode of action of pyoverdine from Pseudomonas fluorescens C7R12 on Arabidopsis (Arabidopsis thaliana) plants grown under iron-sufficient or iron-deficient conditions. Pyoverdine was provided to the medium in its iron-free structure (apo-pyoverdine), thus mimicking a situation in which it is produced by bacteria. Rema…

Cryo-méthodes appliquées à l’étude des interactions entre plantes et Pseudomonas Fluorescents en relation avec le fer dans la rhizosphère

SPEBAPEAIPMBIOmE; Cryo-méthodes appliquées à l’étude des interactions entre plantes et [i]Pseudomonas Fluorescents[/i] en relation avec le fer dans la rhizosphère. 7. Journées Scientifiques et Techniques du Réseau des Microscopistes de l'INRA (RμI)

Characterization and transcriptional analysis of Pseudomonas fluorescens denitrifying clusters containing the nar, nir, nor and nos genes

In this study, we report the cloning and characterization of denitrifying gene clusters of Pseudomonas fluorescens C7R12 containing the narXLDKGHJI, nirPOQSM, norCB and nosRZDFYL genes. While consensus sequences for Fnr-like protein binding sites were identified in the promoter regions of the nar, nir, nor and nos genes, consensus sequences corresponding to the NarL binding sites were identified only upstream the nar genes. Monitoring by mRNA analysis the expression of the narG, nirS, norB and nosZ structural genes suggests a sequential induction of the denitrification system in P. fluorescens.

Diversité et activités microbiennes dans la rhizosphère: des atouts majeurs en agroécologie

National audience; Les rhizodépôts libérés par les plantes stimulent une microflore abondante et active dans la rhizosphère. La diversité des communautés microbiennes correspondantes est influencée par la nature des rhizodépôts (composition, molécules signal) qui diffère selon les génotypes végétaux. Le coût pour la plante correspondant à la libération de ces rhizodépôts est contrebalancé par le bénéfice issu des effets positifs de certaines populations microbiennes rhizosphériques sur la croissance et la santé de la plante-hôte. La connaissance des traits végétaux impliqués dans la sélection de ces populations bénéfiques, au sein des communautés microbiennes telluriques, représente un enje…

Presence of DNA sequences characteristic of type III secretion systems in biocontrol Pseudomonas fluorescens strain C7R12

International audience

Diversity of root-associated fluorescent pseudomonads as affected by ferritin overexpression in tobacco

A transgenic tobacco overexpressing ferritin (P6) was recently shown to accumulate more iron than the wild type (WT), leading to a reduced availability of iron in the rhizosphere and shifts in the pseudomonad community. The impact of the transgenic line on the community of fluorescent pseudomonads was assessed. The diversity of 635 isolates from rhizosphere soils, rhizoplane + root tissues, and root tissues of WT and P6, and that of 98 isolates from uncultivated soil was characterized. Their ability to grow under iron stress conditions was assessed by identifying their minimal inhibitory concentrations of 8-hydroxyquinoline for each isolate, pyoverdine diversity by isoelectrofocusing and ge…

Diversity of TonB-dependent outer-membrane proteins in plant-associated strains of Pseudomonas fluorescens

International audience; Genomic sequences of ten strains of plant-associated Pseudomonas spp. were surveyed for the presence of TonB-dependent outer-membrane proteins (TBDPs), which function in the uptake of substrates from the environment by many Gram-negative bacteria. The ten strains represent P. fluorescens, P. chlororaphis, and P. synxantha isolated from the phyllosphere, rhizosphere or soil. 14 to 45 TBDPs were identified in each strain, and phylogenetic analysis of the TBDPs identified five that are conserved across all ten genomes. Comparisons to proteins with known functions allowed the assignment of putative roles in uptake of heme, vitamin B12, copper, and the siderophore ferrich…

Functional Core microbiota: identification and involvement in plant nutrition

Plants host in their rhizosphere a remarkable diversity of microorganisms that in return can promote plant growth and health. The microbiota that is systematically associated with a given plant genotype is called the core microbiota. However, the core microbiota has been mostly defined on taxonomic basis, whilst the microbiota recruited by the plant in different environments seems to share greater functional similarity and the concept of core functional microbiota has been proposed accordingly. The purpose of the PhD thesis is to give evidence of the existence of a core functional microbiota. The PhD thesis aims to: (i) assess the impact of different plant genotypes on the rhizosphere funct…

Iron dynamics in the rhizosphere as a case study for analysing interactions among soils, plants and microbes

International audience

The impact of the plant-associated siderophore ornicorrugatin on Arabidopsis thaliana

International audience; Most microorganisms produce siderophores when they are faced with iron-limiting conditions. Fluorescent pseudomonads produce a yellow-green, fluorescent siderophore, called pyoverdine. Besides pyoverdine, sev-eral other secondary siderophores, which have a relatively lower affinity for iron, have been identified in Pseu-domonas spp. Examples are pyochelin, pseudomonine and thioquinolobactin (Cornelis and Matthijs 2002). An atypical set of secondary siderophores, due to their lipopeptidic nature, are the siderophores corrugatin (Risse et al., 1998), ornicorrugatin (Matthijs et al., 2008) and histicorrugatin (Matthijs et al., 2016). These siderophores consist out of an…

Déclaration d'invention et de résultats valorisables déposée par Marc Lepetit (LSTM INRA Montpellier) en mars 2018 pour dépôt de Licence d'exploitation exclusive sur savoir-faire (INRA-Transfert/LALLEMAND) 180205F "Souches de Rhizobium leguminosarum bv viciae P1NP1J et P221 pour l’inoculation de légumineuses". Contribution: Isolement d'une collection bactérienne et sélection au sein de cette collection d'une des 2 souches (P221) sur la base de caractérisations moléculaires et fonctionnelles

Influence du système de sécrétion de type III bactérien dans les intéractions plantes-Pseudomonas spp. fluorescents non pathogènes

http://prodinra.inra.fr/record/271693SPEEAEcolDurCT3; L’objectif de cette thèse a été de contribuer à faire progresser les connaissances sur les interactions bénéfiques entre les plantes et les microorganismes en évaluant la contribution des systèmes de sécrétion de type III (SST3). Une synthèse des connaissances disponibles relatives aux SST3 chez les Pseudomonas non pathogènes, saprotrophes ou mutualistes, montre que les SST3 ne sont pas cantonnés aux interactions parasites ou pathogènes avec les plantes. Dans la première étude expérimentale, nous avons utilisé différents génotypes de Medicago truncatula Gaertn. cv. Jemalong capables (Myc+) ou non (Myc-) d’établir une symbiose mycorhizien…

La pyoverdine, un sidérophore produit par la souche bénéfique du sol Pseudomonas fluorescens C7R12, impacte l’homéostasie du fer et promeut la croissance aux dépens des réactions de défense d’Arabidopsis thaliana cultivée en condition de carence en fer

Rôle de la nitrate réductase et de la pyoverdine dans la compétence tellurique et rhizosphérique de la souche Pseudomonas fluorescens C7R12

National audience

Plant/micro-organism interactions in the rhizosphere. Chap 4

Prod 2018-76i EA SPE BIOME INRA AGROSUP; International audience; Soils are environments where a myriad of different organisms evolve, determining a series of functions which translate into ecosystem services that are essential for humanity. Improving our understanding of these organisms, their biodiversity and their interactions with each other, as well as with the environment, represents a major challenge. Soil ecology has its roots in natural history. The ecological approach focused on soils is notable for integrating, at least partially, the contributions of soil sciences (physics, chemistry, biochemistry). By renewing methods of observation and analysis (especially molecular ones) and t…

Implication of pyoverdines in the interactions of fluorescent pseudomonads with soil microflora and plant in the rhizosphere

Soils are known to be oligotrophic environments whereas soil microflora is mostly heterotrophic in such way that microbial growth in soil is mainly limited by the scarce sources of readily available organic compounds (Wardle 1992). Therefore, in soils, microflora is mostly in stasis (fungistasis/bacteriostasis) (Lockwood 1977). In counterpart, plants are autotrophic organisms responsible for the primary production resulting from the photosynthesis. A significant part of photosynthetates are released from plant roots to the soil through a process called rhizodeposition. These products, i.e. the rhizodeposits, are made of exudates, lysates, mucilage, secretions and dead cell material, as well…

Genetic and microscopic study of type III secretion system in Pseudomonas fluorescens

National audience

The competitiveness to form nodules shapes the capacities of Rhizobium leguminosarum sv viciae communities to promote symbiosis with specific hosts

National audience; Cultivated fabeae legumes (pea, fababean, lentil) develop root nodules resulting from the symbiotic interaction with Rhizobium leguminosarum sv. viciae (Rlv). Individual Rlv bacteria are able to associate with various potential hosts, but in soil they are in mixture and they display a wide range of competitiveness to form nodules (CFN). Because in Rlv, CFN and capacity to fix nitrogen are genetically independent, CFN limits the effectiveness of inoculation strategies as efficient bacteria are often outcompeted by poorly efficient Rlv bacteria of the soil community. We developed a strategy to identify bacterial genes controlling CFN. A worldwide collection of 240 Rlv isola…

Phenazine antibiotics produced by fluorescent pseudomonads contribute to natural soil suppressiveness to Fusarium wilt

Natural disease-suppressive soils provide an untapped resource for the discovery of novel beneficial microorganisms and traits. For most suppressive soils, however, the consortia of microorganisms and mechanisms involved in pathogen control are unknown. To date, soil suppressiveness to Fusarium wilt disease has been ascribed to carbon and iron competition between pathogenic Fusarium oxysporum and resident non-pathogenic F. oxysporum and fluorescent pseudomonads. In this study, the role of bacterial antibiosis in Fusarium wilt suppressiveness was assessed by comparing the densities, diversity and activity of fluorescent Pseudomonas species producing 2,4-diacetylphloroglucinol (DAPG) (phlD+) …

Ecologie du microbiote rhizosphérique impliqué dans la dynamique du fer et conséquences sur la teneur en fer des plantes

Le pois représente une espèce particulièrement intéressante en agroécologie pour sa capacité à fixer l’azote atmosphérique, ainsi que pour sa contribution à la diversification des cultures, telles que les cultures associées pois-blé. Une de limitations majeures à la culture du pois est son rendement irrégulier, dû, entre autre, à sa sensibilité à la carence en fer. Le pois est également intéressant pour l’alimentation humaine, compte tenu de la richesse en protéines de ses graines. La part d’alimentation humaine reposant sur les protéines végétales est grandissante, il est donc indispensable de garantir la teneur en fer de ces produits pour limiter la propagation de l’anémie, qui est déjà u…

Analysis of the cross‐regulation between immunity, growth and iron homeostasis in plants

The existence of a tightly regulated balance between growth and immunity in plants has recently emerged. In this study, we challenged this concept thanks to the biological model pyoverdine-Arabidopsis thaliana. Pyoverdine is a siderophore produced by the plant growth promoting rhizobacteria Pseudomonas fluorescens C7R12. Under iron deficiency, P. fluorescens excretes the iron free form of pyoverdine (apo‐pyo) in the soil. Once chelated with iron (ferri‐pyo), the complex is internalized by the bacteria. We demonstrated that Arabidopsis thaliana plants treated by apo‐pyo in a medium containing or not iron internalize pyoverdine. Interestingly, apo‐pyo-treated plants did not show a typical gro…

Report on the interaction between pea and fluorescent pseudomonads and the potential impact on the plant iron nutrition

Présence de séquences d'ADN caractéristiques de systèmes de sécrétion de type III chez l'agent de lutte biologique Pseudomonas fluorescens C7R12

National audience

Variation in the TonB-dependent outer-membrane proteins in plant-associated strains of Pseudomonas fluorescens

International audience; Genomic sequences of ten strains of plant-associated Pseudomonas spp. were surveyed for the presence of TonB-dependent outer-membrane proteins (TBDPs), which function in the uptake of substrates from the environment by many Gram-negative bacteria. The ten strains represent P. fluorescens, P. chlororaphis, and P. synxantha isolated from the phyllosphere, rhizosphere or soil. 14 to 45 TBDPs were identified in each strain, and phylogenetic analysis of the TBDPs identified five that are conserved across all ten genomes. Comparisons to proteins with known functions allowed the assignment of putative roles in uptake of heme, vitamin B12, copper, and the siderophore ferrich…

Toward an integrated approach for studying plant-microbe interactions in the rhizosphere: from genomic to proteomic

International audience

Metabolic fate of a bacterial siderophore in Arabidopsis thaliana and Pisum sativum in relationship with iron status in plants

Despite its abundance, iron is weakly bioavailable for organisms due to its poor solubility in soils under aerobic conditions. Therefore, plants and other organisms have evolved mechanisms to efficiently assimilate iron from the soil. Non-grass plants use a strategy (strategy I) based on soil acidification, reduction of the Fe3+ in Fe2+ which incorporated in the roots by iron transporters. We previously showed (Shirley et al., 2011; Vansuyt et al., 2007) that iron nutrition and growth of a strategy I plant could be promoted by the ferric-complex of the pyoverdine (Fe-pvd), a siderophore produced by microorganisms. If pyoverdine was further localized in planta using different immunological t…

Comment favoriser, à court terme, le passage à l'application des connaissances sur la rhizosphère : des stratégies possibles à mettre en place pour cela ?

National audience

Effect of ferritin overexpression in tobacco on the structure of bacterial and pseudomonad communities associated with the roots

The genetic structures of total bacterial and pseudomonad communities were characterized in rhizosphere soil and rhizoplane+root tissues of tobacco wild type and a ferritin overexpressor transgenic line (P6) by a cultivation-independent method using directly extracted DNA at the end of three consecutive plant cultures. The structure of total bacterial communities was characterized by automated ribosomal intergenic spacer analysis (A-RISA), and that of pseudomonad communities was characterized by PCR-restriction fragment length polymorphism (PCR-RFLP) from DNA amplified with specific primers. The structure of total bacterial communities was significantly modified in the rhizosphere soil by t…

Variable and core functional microbiota associated with seven Medicago truncatula genotypes

The rhizosphere microbiota emerges as a novel component that expands plant adaptation to its environment, and thus paves the way for future breeding approaches. Knowledge regarding the "functional core microbiota", which refers to the microbial taxa bearing essential functions for holobiont fitness, is required to move forward in this area. The aim of the present study was to compare the functional microbiota recruited by different plant genotypes in order to identify itscore and variable components. Seven genotypes of Medicago truncatula (DZA315-16, DZA315-26, DZA045-6, F83005-5, SA028064, Jemalong A17 and J6), representatives of a core collection of 184 genotypes, were studied. Functional…

Transfer of knowledge from fundamental research to practical application in biological nitrogen fixation : prospects and reality

International audience

Antibiosis as a possible mechanism of soil suppressiveness to Fusarium wilts

Effect of arbuscular mycorrhiza establishment on the genetic structure and diversity of bacteria in the rhizosphere of Medicago truncatula

National audience; The rhizosphere is the volume of soil which is influenced by plant root activity. Plant roots release 20% of the photosynthates into the rhizosphere. This process sustains the development of an active free living microflora in the rhizosphere compared to the bulk soil. Plants establish also symbiotic associations with soil microorganisms. Arbuscular mycorrhizas (AM) are mutualistic symbioses between soil fungi and plant roots. AM contribute to plant adaptation to low fertility environments. AM are established by 80% of terrestrial plant families including major crop plants. AM are also ancient symbiosis (400 million years). AM are known to be non-specific associations. Ho…

Interactions durables entre plantes et microorganismes dans les sols

National audience

Reciprocal interactions between plants and fluorescent pseudomonads in relation with iron in the rhizosphere

communication orale invitée; absent

Involvement of pyoverdine and nitrate reductase in the soil and rhizospheric competence of biocontrol Pseudomonas fluorescens strain C7R12

International audience

Influence of pea genotype on root-associated pseudomonads, impact on the plant protection against fungal pathogens

International audience

Conservation of type III secretion system genes inBradyrhizobiumisolated from soybean

International audience; The distribution of rhcRST genes encoding the type III secretion system (T3SS) in a collection of Bradyrhizobium strains was characterized by PCR and Southern blot hybridization. The polymorphism of the corresponding sequences amplified by PCR was characterized by RFLP and sequencing together with those available in the databank. Genomic group I is characterized by the presence of Bradyrhizobium elkanii strains and group II by the presence of B. japonicum and B. liaoningense strains. Highly conserved T3SS-like genes were detected by PCR in all Bradyrhizobium strains isolated from soybean belonging to genomic group II, and in none of the strains belonging to genomic g…

Importance de la diversité des Pseudomonas rhizosphériques et de celle de leurs sidérophores dans la nutrition en fer de la plante hôte

Influence of pea genotype on root associated fluorescent pseudomonads, consequences for plant iron nutrition

Pea has a high potential in agroecology because of its ability to fix atmospheric nitrogen and in Human nutrition because of the high aminoacid content of its grains. However, pea may suffer from a susceptibility to iron deficiency in calcareous soils. This susceptibility varies depending on cultivars. Pseudomonad siderophores, pyoverdines (pvd), were shown to promote iron nutrition in Arabidopsis and tobacco. Thus, we hypothesize that variations in iron susceptibility between pea cultivars could be related to differences in their ability to recruit fluorescent pseudomonad (fp) contributing to siderophore-mediated iron nutrition. Our aims were to compare i) the impact of a susceptible (S) a…

Qu’attendre des recherches en microbiologie du sol ?

SPE EA EcolDur GenoSol MERS IPM Résumé du livre : La fertilité des sols est au carrefour des enjeux de sécurité alimentaire, de protection de l’environnement et de rentabilité économique de l’activité agricole. Cet ouvrage présente les résultats d’une réflexion prospective sur le contexte de la fertilisation dans les 5-10 ans à venir. Il définit les besoins en termes de méthodes et d'outils pour la gestion des cycles biogéochimiques et le raisonnement de la fertilisation en agriculture. Mots clés du livre : agriculture - agronomie - eau - effluent - engrais - environnement - fertilisation - pollution - prévention - production végétale - prospective - sol Description du chapitre 10 (partie 3…

Interaction Pisum sativum (pois)- Pseudomonas: Conséquences sur la nutrition en fer, la croissance et l’immunité de la plante hôte

SPEEABIOMEDOCT INRA; Le projet vise à progresser dans notre connaissances des interactions pois – Pseudomonas afin d’améliorer la nutrition en fer et la santé de la plante-hôte. Le pois représente un fort potentiel en agroécologie (symbiose fixatrice d’azote) et en nutrition humaine (graines riches en acides aminés). Cependant, sa culture est sensible à la carence en fer et à certains phytopathogènes. Pour promouvoir la nutrition en fer et la santé du pois, l’objectif est de valoriser les pyoverdines, sidérophores produits par les Pseudomonas spp. fluorescents, dont certains peuvent améliorer la nutrition en fer de plantes et sont responsables d’antagonisme envers des phytopathogènes. La st…

Implication of pyoverdines in the interactions of fluorescent pseudomonads with soil microflora and plant in the rhizosphere

International audience

Reciprocal interactions between plants and fluorescent pseudomonads in relation with iron in the rhizosphere

National audience; Although iron is the fourth element in the Earth’s crust, the availability of Fe(III) is limited in most cultivated soils due to their pH. In soil adhering to plant roots (rhizosphere), plants release a sgnificant part of their photosynthetates (rhizodeposits) that promote microbial density and activity. Iron uptake by this microflora and by plant roots contributes to decrease even more iron availability in the rhizosphere. In this competition context, plants and microbes have developed active strategies of iron uptake. In dicotyledon plants, this strategy involves (i) the excretion of protons, (ii) the reduction of Fe(III) by reductases, and (iii) plasmalemma transport o…

Fluorescent pseudomonad injectisomes and manipulation of plant defenses : biocontrol versus pathogenic rhizosphere agents

International audience

Reciprocal interactions between plants and fluorescent pseudomonads in relation with iron in the rhizosphere

International audience; Iron is an essential element for plants and microbes. However, in most cultivated soils, the concentration of iron available for these living organisms is very low since its solubility is controlled by stable hydroxides, oxyhydroxides and oxides. The high demand for iron by plants and microorganisms in the rhizosphere together with its low availability in soils leads to a strong competition for this nutrient among living organisms. To face this competition, plants and microorganisms have developed active strategies of iron uptake. In non graminaceous plants (strategy I), iron uptake relies on acidification and reduction of Fe+++ in Fe++ which incorporated in the root…