Arbuscular mycorrhizal fungi reduce the differences in competitiveness between dominant and subordinate plant species

In grassland communities, plants can be classified as dominants or subordinates according to their relative abundances, but the factors controlling such distributions remain unclear. Here, we test whether the presence of the arbuscular mycorrhizal (AM) fungus Glomus intraradices affects the competitiveness of two dominant (Taraxacum officinale and Agrostis capillaris) and two subordinate species (Prunella vulgaris and Achillea millefolium). Plants were grown in pots in the presence or absence of the fungus, in monoculture and in mixtures of both species groups with two and four species. In the absence of G. intraradices, dominants were clearly more competitive than subordinates. In inoculated pots, the fungus acted towards the parasitic end of the mutualism-parasitism continuum and had an overall negative effect on the growth of the plant species. However, the negative effects of the AM fungus were more pronounced on dominant species reducing the differences in competitiveness between dominant and subordinate species. The effects of G. intraradices varied with species composition highlighting the importance of plant community to mediate the effects of AM fungi. Dominant species were negatively affected from the AM fungus in mixtures, while subordinates grew identically with and without the fungus. Therefore, our findings predict that the plant dominance hierarchy may flatten out when dominant species are more reduced than subordinate species in an unfavourable AM fungal relationship (parasitism

Arbuscular mycorrhizal fungi reduce the differences in competitiveness between dominant and subordinate plant species

In grassland communities, plants can be classified as dominants or subordinates according to their relative abundances, but the factors controlling such distributions remain unclear. Here, we test whether the presence of the arbuscular mycorrhizal (AM) fungus Glomus intraradices affects the competitiveness of two dominant (Taraxacum officinale and Agrostis capillaris) and two subordinate species (Prunella vulgaris and Achillea millefolium). Plants were grown in pots in the presence or absence of the fungus, in monoculture and in mixtures of both species groups with two and four species. In the absence of G. intraradices, dominants were clearly more competitive than subordinates. In inoculated pots, the fungus acted towards the parasitic end of the mutualism-parasitism continuum and had an overall negative effect on the growth of the plant species. However, the negative effects of the AM fungus were more pronounced on dominant species reducing the differences in competitiveness between dominant and subordinate species. The effects of G. intraradices varied with species composition highlighting the importance of plant community to mediate the effects of AM fungi. Dominant species were negatively affected from the AM fungus in mixtures, while subordinates grew identically with and without the fungus. Therefore, our findings predict that the plant dominance hierarchy may flatten out when dominant species are more reduced than subordinate species in an unfavourable AM fungal relationship (parasitism)

Experimental warming interacts with soil moisture to discriminate plant responses in an ombrotrophic peatland

International audienceQuestionA better understanding of the response of Sphagnum mosses and associated vascular plants to climate warming is relevant for predicting the carbon balance of peatlands in a warmer world. Open-top chambers (OTCs) have been used to investigate the effect on soil biogeochemical processes in peatlands, but little information is available on the effects of OTCs on microclimate conditions and the associated response of the plant community. We aimed to understand how simulated warming and differences in soil moisture affect plant species cover.LocationA Sphagnum-dominated peatlands in French Jura.MethodsWe used OTCs to measure the effect of a near-ground temperature increase (+1.5 °C on average) on vegetation dynamics over five growing seasons (2008–2012) in a Sphagnum-dominated peatland, in two adjacent microhabitats with different hydrological conditions – wet and dry. Microclimatic conditions and plant species abundance were monitored at peak biomass in years 1, 2, 3 and 5 and monthly during the plant growing season in year 5.ResultsThe response to warming differed between vascular plants and bryophytes, as well as among species within these groups, and also varied in relation to soil moisture. Andromeda polifolia abundance responded positively to warming, while Vaccinium oxycoccus responded negatively, and Eriophorum vaginatum showed a high resistance.ConclusionDepth of rooting of vascular plants appeared to control the response in plant abundance, while moss abundance depended on various other interacting factors, such as shading by the vascular plant community, precipitation and soil moisture

Single-cell immune repertoire sequencing of B and T cells in murine models of infection and autoimmunity

Adaptive immune repertoires are composed by the ensemble of B and T cell receptors (BCR, TCR) within an individual and reflect both past and current immune responses. Recent advances in single-cell sequencing enable recovery of the complete adaptive immune receptor sequences in addition to transcriptional information. Such high-dimensional datasets enable the molecular quantification of clonal selection of B and T cells across a wide variety of conditions such as infection and disease. Due to costs, time required for the analysis and current practices of academic publishing, small-scale sequencing studies are often not made publicly available, despite having informative potential to elucidate immunological principles and guide future-studies. Here, we performed single-cell sequencing of B and T cells to profile clonal selection across murine models of viral infection and autoimmune disease. Specifically, we recovered transcriptome and immune repertoire information for polyclonal T follicular helper cells following acute and chronic viral infection, CD8+ T cells with binding specificity restricted to two distinct peptides of lymphocytic choriomeningitis virus, and B and T cells isolated from the nervous system in the context of experimental autoimmune encephalomyelitis. We could relate repertoire features such as clonal expansion, germline gene usage, and clonal convergence to cell phenotypes spanning activation, memory, naive, antibody secretion, T cell inflation, and regulation. Together, this dataset provides a resource for experimental and computational immunologists that can be integrated with future single-cell immune repertoire and transcriptome sequencing datasets

Single-cell immune repertoire sequencing of B and T cells in murine models of infection and autoimmunity

Adaptive immune repertoires are composed by the ensemble of B and T cell receptors (BCR, TCR) within an individual and reflect both past and current immune responses. Recent advances in single-cell sequencing enable recovery of the complete adaptive immune receptor sequences in addition to transcriptional information. Such high-dimensional datasets enable the molecular quantification of clonal selection of B and T cells across a wide variety of conditions such as infection and disease. Due to costs, time required for the analysis and current practices of academic publishing, small-scale sequencing studies are often not made publicly available, despite having informative potential to elucidate immunological principles and guide future-studies. Here, we performed single-cell sequencing of B and T cells to profile clonal selection across murine models of viral infection and autoimmune disease. Specifically, we recovered transcriptome and immune repertoire information for polyclonal T follicular helper cells following acute and chronic viral infection, CD8+ T cells with binding specificity restricted to two distinct peptides of lymphocytic choriomeningitis virus, and B and T cells isolated from the nervous system in the context of experimental autoimmune encephalomyelitis. We could relate repertoire features such as clonal expansion, germline gene usage, and clonal convergence to cell phenotypes spanning activation, memory, naive, antibody secretion, T cell inflation, and regulation. Together, this dataset provides a resource for experimental and computational immunologists that can be integrated with future single-cell immune repertoire and transcriptome sequencing datasets

Analysis of the contribution of inflammasomes and interleukin-1β in a murine model of microcrystalline inflammation

La goutte est une maladie inflammatoire particulièrement prévalente causée par la formation de dépôts articulaires et péri-articulaires de cristaux d’urate monosodique (UMS ou MSU) et dépendante de la cytokine interleukine-1β (IL-1β). En 2006, l’inflammasome NLRP3 a été montré comme nécessaire pour la maturation de l’IL-1β, in vitro, en réponse aux cristaux de MSU. Néanmoins, sa nécessité in vivo est un sujet de controverse. Mon travail de thèse a porté sur la caractérisation d’un modèle murin d’inflammation aiguë uratique et l’analyse de la contribution des inflammasomes dans cette pathologie. J’ai d’abord montré que notre modèle par injection sous-cutanée de cristaux de MSU donne lieu une forte inflammation des tissus mous comme cela est souvent observé lors des crises de goutte chez l’Homme. L’emploi de souris invalidées génétiquement et d’inhibitions pharmacologiques m’a permis de décrire son indépendance vis-à-vis de plusieurs composants des inflammasomes et confirme le rôle majeur de l’IL-1β. De manière intéressante, j’ai ensuite montré qu’il est possible de réduire fortement l’inflammation dans ce modèle par un traitement topique à base d’imiquimod (crème ALDARA®), un ligand synthétique de TLR7. Des expériences réalisées in vivo et in vitro m’ont permis de relier l’effet de l’imiquimod à une baisse importante de l’Il1b au niveau transcriptionel, via une signalisation faisant probablement intervenir les interférons de type I et possiblement le facteur RUNX3. Mes données montrent donc que la production d’IL-1β, dans ce modèle, est visiblement indépendante de NLRP3 mais peut être fortement abaissée par l’application topique d’imiquimod. L’imiquimod pourrait ainsi représenter une piste thérapeutique attractive.Gout is a prevalent inflammatory disease caused by the deposition of monosodium urate crystals (MSU) in articular/periarticular areas, which strongly depends on interleukine-1β (IL-1β). In 2006, the NLRP3 inflammasome has been shown to perform IL-1β maturation in vitro after MSU crystal exposure. However, its in vivo dependence is still matter of controversy. In my thesis project, I focused on the characterization of a murine acute uratic inflammation and analysed the contribution of inflammasome components. I first showed that the subcutaneous injection of MSU crystals in mice generate a strong soft tissue inflammation as observed in human gouty crises. Then, by using genetically-modified mouse lines and pharmacological inhibitions, I demonstrated that this model is inflammasome-independent, while still requiring IL-1β secretion. Interestingly, I observed that the topical application of imiquimod (ALDARA® cream), which is a synthetic TLR7 ligand, strongly dampens inflammation. In vivo and in vitro experiments further demonstrated that this effect is linked to reduced Il1b gene expression, which linkely involves type I interferon signaling and eventually the transcription factor RUNX3. Altogether, my results show that IL-1β production is NLRP3-independent in this mouse model but can be strongly decreased by topical application of imiquimod. Therefore, imiquimod might be an attractive therapeutic option for gouty patients

Analysis of the contribution of inflammasomes and interleukin-1β in a murine model of microcrystalline inflammation

La goutte est une maladie inflammatoire particulièrement prévalente causée par la formation de dépôts articulaires et péri-articulaires de cristaux d’urate monosodique (UMS ou MSU) et dépendante de la cytokine interleukine-1β (IL-1β). En 2006, l’inflammasome NLRP3 a été montré comme nécessaire pour la maturation de l’IL-1β, in vitro, en réponse aux cristaux de MSU. Néanmoins, sa nécessité in vivo est un sujet de controverse. Mon travail de thèse a porté sur la caractérisation d’un modèle murin d’inflammation aiguë uratique et l’analyse de la contribution des inflammasomes dans cette pathologie. J’ai d’abord montré que notre modèle par injection sous-cutanée de cristaux de MSU donne lieu une forte inflammation des tissus mous comme cela est souvent observé lors des crises de goutte chez l’Homme. L’emploi de souris invalidées génétiquement et d’inhibitions pharmacologiques m’a permis de décrire son indépendance vis-à-vis de plusieurs composants des inflammasomes et confirme le rôle majeur de l’IL-1β. De manière intéressante, j’ai ensuite montré qu’il est possible de réduire fortement l’inflammation dans ce modèle par un traitement topique à base d’imiquimod (crème ALDARA®), un ligand synthétique de TLR7. Des expériences réalisées in vivo et in vitro m’ont permis de relier l’effet de l’imiquimod à une baisse importante de l’Il1b au niveau transcriptionel, via une signalisation faisant probablement intervenir les interférons de type I et possiblement le facteur RUNX3. Mes données montrent donc que la production d’IL-1β, dans ce modèle, est visiblement indépendante de NLRP3 mais peut être fortement abaissée par l’application topique d’imiquimod. L’imiquimod pourrait ainsi représenter une piste thérapeutique attractive.Gout is a prevalent inflammatory disease caused by the deposition of monosodium urate crystals (MSU) in articular/periarticular areas, which strongly depends on interleukine-1β (IL-1β). In 2006, the NLRP3 inflammasome has been shown to perform IL-1β maturation in vitro after MSU crystal exposure. However, its in vivo dependence is still matter of controversy. In my thesis project, I focused on the characterization of a murine acute uratic inflammation and analysed the contribution of inflammasome components. I first showed that the subcutaneous injection of MSU crystals in mice generate a strong soft tissue inflammation as observed in human gouty crises. Then, by using genetically-modified mouse lines and pharmacological inhibitions, I demonstrated that this model is inflammasome-independent, while still requiring IL-1β secretion. Interestingly, I observed that the topical application of imiquimod (ALDARA® cream), which is a synthetic TLR7 ligand, strongly dampens inflammation. In vivo and in vitro experiments further demonstrated that this effect is linked to reduced Il1b gene expression, which linkely involves type I interferon signaling and eventually the transcription factor RUNX3. Altogether, my results show that IL-1β production is NLRP3-independent in this mouse model but can be strongly decreased by topical application of imiquimod. Therefore, imiquimod might be an attractive therapeutic option for gouty patients

Analyse de la contribution des inflammasomes et de l’interleukine-1β dans un modèle murin d’inflammation microcristalline

Gout is a prevalent inflammatory disease caused by the deposition of monosodium urate crystals (MSU) in articular/periarticular areas, which strongly depends on interleukine-1β (IL-1β). In 2006, the NLRP3 inflammasome has been shown to perform IL-1β maturation in vitro after MSU crystal exposure. However, its in vivo dependence is still matter of controversy. In my thesis project, I focused on the characterization of a murine acute uratic inflammation and analysed the contribution of inflammasome components. I first showed that the subcutaneous injection of MSU crystals in mice generate a strong soft tissue inflammation as observed in human gouty crises. Then, by using genetically-modified mouse lines and pharmacological inhibitions, I demonstrated that this model is inflammasome-independent, while still requiring IL-1β secretion. Interestingly, I observed that the topical application of imiquimod (ALDARA® cream), which is a synthetic TLR7 ligand, strongly dampens inflammation. In vivo and in vitro experiments further demonstrated that this effect is linked to reduced Il1b gene expression, which linkely involves type I interferon signaling and eventually the transcription factor RUNX3. Altogether, my results show that IL-1β production is NLRP3-independent in this mouse model but can be strongly decreased by topical application of imiquimod. Therefore, imiquimod might be an attractive therapeutic option for gouty patients.La goutte est une maladie inflammatoire particulièrement prévalente causée par la formation de dépôts articulaires et péri-articulaires de cristaux d’urate monosodique (UMS ou MSU) et dépendante de la cytokine interleukine-1β (IL-1β). En 2006, l’inflammasome NLRP3 a été montré comme nécessaire pour la maturation de l’IL-1β, in vitro, en réponse aux cristaux de MSU. Néanmoins, sa nécessité in vivo est un sujet de controverse. Mon travail de thèse a porté sur la caractérisation d’un modèle murin d’inflammation aiguë uratique et l’analyse de la contribution des inflammasomes dans cette pathologie. J’ai d’abord montré que notre modèle par injection sous-cutanée de cristaux de MSU donne lieu une forte inflammation des tissus mous comme cela est souvent observé lors des crises de goutte chez l’Homme. L’emploi de souris invalidées génétiquement et d’inhibitions pharmacologiques m’a permis de décrire son indépendance vis-à-vis de plusieurs composants des inflammasomes et confirme le rôle majeur de l’IL-1β. De manière intéressante, j’ai ensuite montré qu’il est possible de réduire fortement l’inflammation dans ce modèle par un traitement topique à base d’imiquimod (crème ALDARA®), un ligand synthétique de TLR7. Des expériences réalisées in vivo et in vitro m’ont permis de relier l’effet de l’imiquimod à une baisse importante de l’Il1b au niveau transcriptionel, via une signalisation faisant probablement intervenir les interférons de type I et possiblement le facteur RUNX3. Mes données montrent donc que la production d’IL-1β, dans ce modèle, est visiblement indépendante de NLRP3 mais peut être fortement abaissée par l’application topique d’imiquimod. L’imiquimod pourrait ainsi représenter une piste thérapeutique attractive

Species identity, rather than species mixtures, drives cover crop effects on nutrient partitioning in unfertilized agricultural soil

International audienc