Agnès Robin
University of Burgundy
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Featured researches published by Agnès Robin.
Molecular Plant-microbe Interactions | 2007
Gérard Vansuyt; Agnès Robin; Jean-François Briat; Catherine Curie; Philippe Lemanceau
Taking into account the strong iron competition in the rhizosphere and the high affinity of pyoverdines for Fe(III), these molecules are expected to interfere with the iron nutrition of plants, as they do with rhizospheric microbes. The impact of Fe-pyoverdine on iron content of Arabidopsis thaliana was compared with that of Fe-EDTA. Iron chelated to pyoverdine was incorporated in a more efficient way than when chelated to EDTA, leading to increased plant growth of the wild type. A transgenic line of A. thaliana overexpressing ferritin showed a higher iron content than the wild type when supplemented with Fe-EDTA but a lower iron content when supplemented with Fe-pyoverdine despite its increased reductase activity, suggesting that this activity was not involved in the iron uptake from pyoverdine. A mutant knock-out iron transporter IRT1 showed lower iron and chlorophyll contents when supplemented with Fe-EDTA than the wild type but not when supplemented with Fe-pyoverdine, indicating that, in contrast to iron from EDTA, iron from pyoverdine was not incorporated through the IRT1 transporter. Altogether these data suggest that iron from Fe-pyoverdine was not incorporated in planta through the strategy I, which is based on reductase activity and IRT1 transporter. This is supported by the presence of pyoverdine in planta as shown by enzyme-linked immunosorbent assay and by tracing 15N of 15N-pyoverdine.
Advances in Agronomy | 2008
Agnès Robin; Gérard Vansuyt; Philippe Hinsinger; Jean-Marie Meyer; Jean-François Briat; Philippe Lemanceau
Abstract Iron is an essential micronutrient for most organisms due to its role in fundamental metabolic processes. In cultivated soils, soil solution iron is mostly oxidized [Fe(III) species] unless local anoxic conditions develop. The concentration of these Fe(III) species is small in soil solution due to the low solubility of ferric oxides, oxyhydroxides, and hydroxides, which is minimal at neutral and alkaline pH. In the rhizosphere, iron concentration in the soil solution is even lower because of its uptake by aerobic organisms (plants and microorganisms), leading to a high level of competition for Fe(III). In order to face iron competition, these organisms have evolved active uptake strategies based on acidification, chelation, and/or reduction processes. Iron competition plays a major role in microbial and plant–microbe interactions in the rhizosphere. This review summarizes current knowledge on the iron status in soils and rhizospheres, and the acquisition strategies of plants and microbes. This review also shows how the dynamic interactions between soil minerals, plants, and microorganisms impact plant health and nutrition. Analysis of these complex interactions offers an interesting case study of research on rhizosphere ecology integrating different scientific expertises and approaches.
FEMS Microbiology Ecology | 2011
Amandine Viollet; Thérèse Corberand; Christophe Mougel; Agnès Robin; Philippe Lemanceau; Sylvie Mazurier
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 fragment length polymorphism and sequencing. Genotypic diversity of all pseudomonads isolated, whether or not harboring T3SS, was described by BOX-PCR. T3SS+ pseudomonads were significantly more abundant in mycorrhizal than in nonmycorrhizal roots and in bulk soil, and all were shown to belong to the phylogenetic group of Pseudomonas fluorescens on the basis of 16S rRNA gene identity. Four hrcRST genotypes were described; two only included isolates from mycorrhizal roots. T3SS+ and T3SS- pseudomonads showed different genetic backgrounds as indicated by their different BOX-PCR types. Taken together, these data suggest that T3SSs are implicated in interactions between fluorescent pseudomonads and AM in medic rhizosphere.
Plant and Soil | 2006
Agnès Robin; Gérard Vansuyt; Thérèse Corberand; Jean-François Briat; Philippe Lemanceau
Transgenic tobacco P6 over-expressing ferritin is known to activate iron transport systems and to have increased iron content. Iron phytoextraction by this transgene is then expected to be higher than that of the wild-type (WT). In the present study, the possibility to modify iron availability for bacteria via the cultivation of the transgene P6 was explored by comparing the sensitivity to iron stress of bacteria isolated from the rhizosphere of the two plant genotypes (WT and P6). This sensitivity was evaluated by measuring the bacterial density when plated on a solid media depleted (supplemented with 8-hydroxiquinoline) or not (supplemented with Fe-8-hydroxyquinoline) in iron. The experimental conditions favorable to the differential iron accumulation between the wild-type and transgenic tobacco were identified. The two plant genotypes were grown in three soils (Hervau, Thory and Oudun) chosen for their differences in iron content, and the plants were yielded at three stages (vegetative, floral bud and flowering). The highest differential accumulation of iron in favor of the over-expressing transgene was found in the plants at the floral bud stage when cultivated in the Oudun and Thory soils. Since at that stage, the plant growth was significantly higher in the Oudun soil, the phytoextraction of iron was the highest in this soil. At the floral bud stage, bacteria isolated from the rhizosphere of the transgene cultivated in the Oudun and Thory soils appeared to be less susceptible to iron stress than those from the wild-type. Bacterial density recovered on agar medium depleted in iron was significantly the highest in the rhizosphere of the transgene cultivated in the Oudun soil. Altogether, these data indicate that the over-expressing ferritin transgenic plants, that accumulate and extract more iron from the rhizosphere than the wild-type plants, select in their rhizosphere bacteria less susceptible to iron stress compared to those selected by the wild-type plants.
Plant and Soil | 2016
Xiaoyan Tang; Sarah Placella; Florent Daydé; Laetitia Bernard; Agnès Robin; Etienne-Pascal Journet; Eric Justes; Philippe Hinsinger
Background and aimsPositive below-ground interactions (facilitation) should be more pronounced when resources limit crop growth, according to the stress-gradient hypothesis. Our aim was to test this hypothesis for intercropped durum wheat and faba bean along a P-fertilizer gradient.MethodsA field experiment was conducted in a long-term P-fertilizer trial with three rates of P-fertilization (No, Low and High P). Microbial biomass was assessed by chloroform fumigation-extraction. Quantitative PCR was applied to evaluate the abundance of relevant microbial groups.ResultsPhosphorus availability and microbial biomass systematically increased in the rhizosphere compared to bulk soil. P-fertilization resulted in higher abundance of targeted bacterial phyla, whole bacterial and fungal communities, and depressed mycorrhizal colonization of durum wheat, but not faba bean. Microbial biomass carbon significantly increased in the rhizosphere only in P-fertilized treatments, pointing to P limitation of microbial communities. Intercropping yielded a significant effect on rhizosphere microbial properties only at High P. Microbial biomass P increased in the rhizosphere of intercropped faba bean only at No P level, and was thus the sole finding supporting the stress-gradient hypothesis.ConclusionsP-fertilization was the main driver of microbial communities in this field trial, and P-fertilizer application modulated the species-specific effect in the intercrop. Plant performance did not validate the stress-gradient hypothesis as positive plant-plant interactions occurred regardless of the level of P-fertilization.
Archive | 2007
Philippe Lemanceau; Agnès Robin; Sylvie Mazurier; Gérard Vansuyt
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 as gases including respiratory CO2 and ethylene. Depending on plant species, age and environmental conditions, rhizodeposits can account for up to 40% of net fixed carbon (Lynch and Whipps 1990). On average, 17% of net fixed carbon appears to be released by the roots (Nguyen 2003). This significant release of organic compounds by plant roots in soil oligotrophic environments is then expected to affect strongly the heterotrophic microflora located closely to the roots. Indeed, one century ago, Hiltner (1904) observed an increased proliferation of heterotrophic bacteria in contact with the roots. This author proposed to call rhizosphere the volume of soil surrounding roots in which the microflora is influenced by these roots. Since then, further studies have shown that living roots modify the biological and physicochemical properties of rhizospheric soil determining the rhizosphere effect (Curl and Truelove 1986; Lemanceau and Heulin 1998; Lynch 1990; Rovira 1965). Rhizodeposition affects the soil microflora and especially leads to (i) an increase of its density (Clark 1949; Rovira 1965), biomass (Barber and Lynch 1977) 8 Implication of Pyoverdines in the Interactions of Fluorescent Pseudomonads with Soil Microflora and Plant in the Rhizosphere
MC Microscopy Conference - First Joint Meeting of Dreiländertagung & Multinational Congress on Microscopy | 2013
Philippe Lemanceau; Sylvie Mazurier; Laure Avoscan; Agnès Robin; Jean-François Briat
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 roots by iron transporters. Active iron uptake by microorganisms relies on siderophores showing high affinity for iron. We have previously shown that plants of Arabidopsis thaliana (strategy I) supplemented with Fe-pyoverdine had a higher iron content than those supplemented Fe- EDTA [1]. Iron from pyoverdine was not incorporated through the major iron transporter IRT1 as indicated by the similar iron content of the wild-type plant and IRT1 mutant knockout iron transporter IRT1. Furthermore, pyoverdine was shown to be incorporated as indicated by its presence in planta based on enzyme-linked immunosorbent assay measurement of pyoverdine and on 15N of 15N-pyoverdine. Taken together, these observations suggest that iron from Fe-pyoverdine was not incorporated in planta through the strategy I. In the present, we explored the possible incorporation of iron from pyoverdine at the cellular level. For that purpose, on Arabidopsis when cultivated in the presence of Fe-EDTA (50µM) or Fe-pyoverdine (50µM), we analyzed the immunolocalization of pyoverdine in roots by confocal microscopy and performed ultrastructural studies with transmission electron microscopy (TEM). Plants were cultivated in vitro with these chelates during seven days. Immunolabeling were performed with pyoverdine antibody as primary antibody and fluorescent secondary antibody for confocal microscopy and colloidal gold coupled to secondary antibody for immunogold labeling by TEM. Observations with confocal microscopy clearly indicated the presence of pyoverdine in fresh tissue sections. This immunolocalization revealed the presence of pyoverdine in root apoplasmic space. Observations with TEM showed the more abundant presence of vesicles in root apoplasm of plants when cultured with Fe-pyoverdine than with Fe-EDTA (Figure 1). Despite that pyoverdine immunogold labeling of roots sections did not allow to reveal the formal presence of pyoverdine in these vesicles, the present results suggest that the incorporation of Fe- pyoverdine might rely on endocytosis.
Environmental Microbiology | 2007
Agnès Robin; Sylvie Mazurier; Christophe Mougel; Gérard Vansuyt; Thérèse Corberand; Jean-Marie Meyer; Philippe Lemanceau
PSP5 2014 - Facing Phosphorus Scarcity | 2014
Elodie Betencourt; Xiaoyan Tang; Sarah Placella; Agnès Robin; Jianbo Shen; Fusuo Zhang; Philippe Hinsinger
PSP5 2014 - Facing Phosphorus Scarcity | 2014
Esther Guillot; Camille Cros; Sarah Placella; Josiane Abadie; Gabrielle Daudin; Claire Marsden; Agnès Robin; Jean Trap; Philippe Hinsinger