Multiple glacial refugia and contemporary dispersal shape the genetic structure of an endemic amphibian from the Pyrenees

Historical factors (colonization scenarios, demographic oscillations) and contemporary processes (population connectivity, current population size) largely contribute to shaping species’ present-day genetic diversity and structure. In this study, we use a combination of mitochondrial and nuclear DNA markers to understand the role of Quaternary climatic oscillations and present-day gene flow dynamics in determining the genetic diversity and structure of the newt Calotriton asper (Al. Dugès, 1852), endemic to the Pyrenees. Mitochondrial DNA did not show a clear phylogeographic pattern and presented low levels of variation. In contrast, microsatellites revealed five major genetic lineages with admixture patterns at their boundaries. Approximate Bayesian computation analyses and linear models indicated that the five lineages likely underwent separate evolutionary histories and can be tracked back to distinct glacial refugia. Lineage differentiation started around the Last Glacial Maximum at three focal areas (western, central and eastern Pyrenees) and extended through the end of the Last Glacial Period in the central Pyrenees, where it led to the formation of two more lineages. Our data revealed no evidence of recent dispersal between lineages, whereas borders likely represent zones of secondary contact following expansion from multiple refugia. Finally, we did not find genetic evidence of sex-biased dispersal. This work highlights the importance of integrating past evolutionary processes and present-day gene flow and dispersal dynamics, together with multilocus approaches, to gain insights into what shaped the current genetic attributes of amphibians living in montane habitats.info:eu-repo/semantics/publishedVersio

Autophagy as a possible mechanism for micronutrient remobilization from leaves to seeds.

Seed formation is an important step of plant development which depends on nutrient allocation. Uptake from soil is an obvious source of nutrients which mainly occurs during vegetative stage. Because seed filling and leaf senescence are synchronized, subsequent mobilization of nutrients from vegetative organs also play an essential role in nutrient use efficiency, providing source-sink relationships. However, nutrient accumulation during the formation of seeds may be limited by their availability in source tissues. While several mechanisms contributing to make leaf macronutrients available were already described, little is known regarding micronutrients such as metals. Autophagy, which is involved in nutrient recycling, was already shown to play a critical role in nitrogen remobilization to seeds during leaf senescence. Because it is a non-specific mechanism, it could also control remobilization of metals. This article reviews actors and processes involved in metal remobilization with emphasis on autophagy and methodology to study metal fluxes inside the plant. A better understanding of metal remobilization is needed to improve metal use efficiency in the context of biofortification

Autophagy is essential for optimal translocation for iron to seeds in Arabidopsis

Micronutrient deficiencies affect a large part of the world population. They are mostly due to the consumption of grains with insufficient content of Fe or Zn. It is therefore important to improve our knowledge of the mechanisms of micronutrient loading to seeds. Nutrient loaded in seeds originate either from de novo uptake by roots or recycling from leaves. Autophagy is a conserved mechanism for nutrient recycling in eukaryotes and was shown to be involved in nitrogen remobilization to seeds. Measuring the distribution of metal nutrients at the end of the life in Arabidopsis thaliana plants impaired in autophagy, we have investigated the role of autophagy in metal micronutrient translocation to seeds. We found that several Arabidopsis genotypes impaired in autophagy display defects in nutrient remobilization to seeds. In atg5-1, which is completely defective in autophagy, the efficiency of Fe translocation from vegetative organs to seeds was severely decreased even when Fe was provided during seed formation. Combining atg5-1 with sid2 mutation that counteracts premature senescence associated to autophagy deficiency and using 57Fe pulse labelling, we could propose a two step mechanism in which iron taken up de novo during seed formation is first accumulated in vegetative organs and subsequently remobilized to seeds. Finally, we showed that translocations of zinc and manganese to seeds are also dependent on autophagy. Our results highlight the importance of autophagy for optimal micronutrient remobilization to seeds. Fine tuning autophagy during seed formation opens new possibilities to improve this trait

The Nicotiana tabacum ABC transporter NtPDR3 secretes O-methylated coumarins in response to iron deficiency

Although iron is present in large amounts in the soil, its poor solubility means that plants have to use various strategies to facilitate its uptake. In this study, we show that expression of NtPDR3/NtABCG3, a Nicotiana tabacum plasma-membrane ABC transporter in the pleiotropic drug resistance (PDR) subfamily, is strongly induced in the root epidermis under iron deficiency conditions. Prevention of NtPDR3 expression resulted in N. tabacum plants that were less tolerant to iron-deficient conditions, displaying stronger chlorosis and slower growth than those of the wildtype when not supplied with iron. Metabolic profiling of roots and root exudates revealed that, upon iron deficiency, secretion of catechol-bearing O-methylated coumarins such as fraxetin, hydroxyfraxetin, and methoxyfraxetin to the rhizosphere was compromised in NtPDR3-silenced plants. However, exudation of flavins such as riboflavin was not markedly affected by NtPDR3-silencing. Expression of NtPDR3 in N. tabacum Bright Yellow-2 (BY-2) cells resulted in altered intra- and extracellular coumarin pools, supporting coumarin transport by this transporter. The results demonstrate that N. tabacum secretes both coumarins and flavins in response to iron deficiency and that NtPDR3 plays an essential role in the plant response to iron deficiency by mediating secretion of O-methylated coumarins to the rhizosphere

Metal remobilization during leaf senescence : evaluation of the NRAMP involvement in this process in the context of the phytoremediation strategy

Depuis le début des années 1990, différentes stratégies de phytoremédiation ont été proposées pour réhabiliter les zones polluées par des éléments traces métalliques (ETM). Parmi ces stratégies, la phytoextraction consiste en l’absorption et l’accumulation par les plantes des ETM présents dans les sols. Afin de mettre en place cette stratégie, il a été proposé d’utiliser le peuplier en raison de sa croissance rapide, de son importante biomasse et de ses débouchés énergétiques. Cependant une proportion considérable des métaux absorbés par cet arbre est accumulée dans les feuilles alors que celles-ci chutent à l’automne. Ainsi, l’efficacité de phytoextraction du peuplier peut se trouver limitée si aucun mécanisme de remobilisation des ETM n’est mis en place au cours de la sénescence automnale. Dans ce contexte, une partie des travaux de cette thèse a été réalisée sur la parcelle expérimentale de Pierrelaye polluée suite à l’épandage d’eaux usées de la ville de Paris. Nous avons recherché parmi les 14 génotypes de peuplier présents sur le site, ceux qui sont les plus efficaces pour remobiliser les métaux des feuilles vers les parties pérennes. Des mesures de contenu en métaux, d’expression de gènes et des analyses corrélatives ont ouvert de nouvelles pistes concernant la gestion des métaux foliaires. Parce que la vacuole constitue le principal lieu de stockage des métaux de la cellule, les protéines d’efflux vacuolaire NRAMP (Natural Resistance-Associated Macrophage Protein) précédemment identifiées chez Arabidopsis thaliana, représentent de bons candidats pour stimuler la remobilisation des métaux foliaires. La caractérisation de leurs homologues chez le peuplier a donc été entreprise par expression chez la levure et chez A. thaliana. Afin de contrôler indépendamment le transport des métaux essentiels et non-essentiels chez les NRAMP, une étude visant à identifier les déterminants structuraux impliqués dans leur sélectivité a été réalisée. La caractérisation des mutants NRAMP affectés dans leur sélectivité par expression chez A. thaliana a mis en lumière leur impact sur l’accumulation et la tolérance aux métaux. Dans le but d’étudier l’implication de mécanismes plus généraux de recyclage des nutriments dans la remobilisation des métaux au cours de la sénescence foliaire, le rôle de l’autophagie a été testé chez A. thaliana. L’étude de plantes déficientes pour l’autophagie a montré l’implication de ce mécanisme dans l’efficacité d’utilisation des métaux et probablement dans leur remobilisation au cours de la sénescence. En combinant des études en champ sur le peuplier et de génétique moléculaire chez Arabidopsis, ce travail permet de proposer différentes pistes pour diminuer spécifiquement l’accumulation des ETM dans les feuilles de peuplier.Since the early 1990s, various strategies have been proposed to rehabilitate trace element (TE) polluted areas by phytoremediation. Among these strategies, phytoextraction consists in TE uptake from soil and accumulation by plants. To implement this strategy, it has been proposed to use poplar due to its fast growth, its large biomass and its use in energy production. However, a substantial proportion of absorbed metals is accumulated in poplar leaves which fall in autumn. Thus, poplar phytoextraction efficiency may be limited if TE are not re-mobilized during autumn senescence. In this context, part of this thesis work has been carried out on the experimental field of Pierrelaye which was polluted by the spreading of sewage water from Paris. Among the 14 poplar genotypes growing on the field, we tried to identify those that efficiently remobilize leaf metals to perennial organs. Metal content, gene expression and correlative analyses have been undertaken, providing new insight in the management of metals in leaves. Because the vacuole is the main metal storage compartment in the cell, NRAMP (Natural Resistance-Associated Macrophage Protein) vacuolar efflux proteins previously identified in Arabidopsis thaliana are good candidates to enhance leaf metal remobilization. Characterization of their homologues in poplar was therefore undertaken by expression in yeast and in A. thaliana. In order to independently control the transport of essential and non-essential metals by NRAMP, a study aiming to identify the structural determinants involved in selectivity was undertaken. Expression of NRAMP mutants affected in their selectivity in A. thaliana highlighted their impact on metal accumulation and tolerance. To study the involvement of more general nutrient recycling mechanisms in metal remobilization during leaf senescence, the involvement of autophagy was tested in A. thaliana. Physiological characterization of autophagy deficient plants indicated that this mechanism plays a role in metal use efficiency and probably in metal remobilization during senescence. By combining a field approach on poplar and molecular genetics in Arabidopsis, this work opens multiple perspectives to specifically reduce the accumulation of TE in poplar leaves

Étude de la remobilisation des métaux au cours de la sénescence foliaire : évaluation de l’implication des NRAMP dans ce processus dans le cadre de la stratégie de phytoremédiation

Since the early 1990s, various strategies have been proposed to rehabilitate trace element (TE) polluted areas by phytoremediation. Among these strategies, phytoextraction consists in TE uptake from soil and accumulation by plants. To implement this strategy, it has been proposed to use poplar due to its fast growth, its large biomass and its use in energy production. However, a substantial proportion of absorbed metals is accumulated in poplar leaves which fall in autumn. Thus, poplar phytoextraction efficiency may be limited if TE are not re-mobilized during autumn senescence. In this context, part of this thesis work has been carried out on the experimental field of Pierrelaye which was polluted by the spreading of sewage water from Paris. Among the 14 poplar genotypes growing on the field, we tried to identify those that efficiently remobilize leaf metals to perennial organs. Metal content, gene expression and correlative analyses have been undertaken, providing new insight in the management of metals in leaves. Because the vacuole is the main metal storage compartment in the cell, NRAMP (Natural Resistance-Associated Macrophage Protein) vacuolar efflux proteins previously identified in Arabidopsis thaliana are good candidates to enhance leaf metal remobilization. Characterization of their homologues in poplar was therefore undertaken by expression in yeast and in A. thaliana. In order to independently control the transport of essential and non-essential metals by NRAMP, a study aiming to identify the structural determinants involved in selectivity was undertaken. Expression of NRAMP mutants affected in their selectivity in A. thaliana highlighted their impact on metal accumulation and tolerance. To study the involvement of more general nutrient recycling mechanisms in metal remobilization during leaf senescence, the involvement of autophagy was tested in A. thaliana. Physiological characterization of autophagy deficient plants indicated that this mechanism plays a role in metal use efficiency and probably in metal remobilization during senescence. By combining a field approach on poplar and molecular genetics in Arabidopsis, this work opens multiple perspectives to specifically reduce the accumulation of TE in poplar leaves.Depuis le début des années 1990, différentes stratégies de phytoremédiation ont été proposées pour réhabiliter les zones polluées par des éléments traces métalliques (ETM). Parmi ces stratégies, la phytoextraction consiste en l’absorption et l’accumulation par les plantes des ETM présents dans les sols. Afin de mettre en place cette stratégie, il a été proposé d’utiliser le peuplier en raison de sa croissance rapide, de son importante biomasse et de ses débouchés énergétiques. Cependant une proportion considérable des métaux absorbés par cet arbre est accumulée dans les feuilles alors que celles-ci chutent à l’automne. Ainsi, l’efficacité de phytoextraction du peuplier peut se trouver limitée si aucun mécanisme de remobilisation des ETM n’est mis en place au cours de la sénescence automnale. Dans ce contexte, une partie des travaux de cette thèse a été réalisée sur la parcelle expérimentale de Pierrelaye polluée suite à l’épandage d’eaux usées de la ville de Paris. Nous avons recherché parmi les 14 génotypes de peuplier présents sur le site, ceux qui sont les plus efficaces pour remobiliser les métaux des feuilles vers les parties pérennes. Des mesures de contenu en métaux, d’expression de gènes et des analyses corrélatives ont ouvert de nouvelles pistes concernant la gestion des métaux foliaires. Parce que la vacuole constitue le principal lieu de stockage des métaux de la cellule, les protéines d’efflux vacuolaire NRAMP (Natural Resistance-Associated Macrophage Protein) précédemment identifiées chez Arabidopsis thaliana, représentent de bons candidats pour stimuler la remobilisation des métaux foliaires. La caractérisation de leurs homologues chez le peuplier a donc été entreprise par expression chez la levure et chez A. thaliana. Afin de contrôler indépendamment le transport des métaux essentiels et non-essentiels chez les NRAMP, une étude visant à identifier les déterminants structuraux impliqués dans leur sélectivité a été réalisée. La caractérisation des mutants NRAMP affectés dans leur sélectivité par expression chez A. thaliana a mis en lumière leur impact sur l’accumulation et la tolérance aux métaux. Dans le but d’étudier l’implication de mécanismes plus généraux de recyclage des nutriments dans la remobilisation des métaux au cours de la sénescence foliaire, le rôle de l’autophagie a été testé chez A. thaliana. L’étude de plantes déficientes pour l’autophagie a montré l’implication de ce mécanisme dans l’efficacité d’utilisation des métaux et probablement dans leur remobilisation au cours de la sénescence. En combinant des études en champ sur le peuplier et de génétique moléculaire chez Arabidopsis, ce travail permet de proposer différentes pistes pour diminuer spécifiquement l’accumulation des ETM dans les feuilles de peuplier

Exemples d’applications de la télédétection en prairies semi-naturelles

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