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Environmental science & technology 57(7), 2768 - 2778 (2023). doi:10.1021/acs.est.2c06985, Rare earth elements (REEs) are strategic metals strongly involved in low-carbon energy conversion. However, these emerging contaminants are increasingly disseminated into ecosystems, raising concern regarding their toxicity. REE-accumulating plants are crucial subjects to better understand REE transfer to the trophic chain but are also promising phytoremediation tools. In this analysis, we deciphered REE accumulation sites in the REE-accumulating fern Dryopteris erythrosora by synchrotron X-ray μfluorescence (μXRF). This technique allows a high-resolution and in situ analysis of fresh samples or frozen-hydrated cross sections of different organs of the plant. In the sporophyte, REEs were translocated from the roots to the fronds by the xylem sap and were stored within the xylem conductive system. The comparison of REE distribution and accumulation levels in the healthy and necrotic parts of the frond shed light on the differential mobility between light and heavy REEs. Furthermore, the comparison emphasized that necrotized areas were not the main REE-accumulating sites. Finally, the absence of cell-to-cell mobility of REEs in the gametophyte suggested the absence of REE-compatible transporters in photosynthetic tissues. These results provide valuable knowledge on the physiology of REE-accumulating ferns to understand the REE cycle in biological systems and the expansion of phytotechnologies for REE-enriched or REE-contaminated soils., Published by American Chemical Society, Columbus, Ohio

International audience; The rapid development of green energy sources and new medical technologies contributes to the increased exploitation of rare earth elements (REEs). They can be subdivided into light (LREEs) and heavy (HREEs) REEs. Mining, industrial processing, and end-use practices of REEs has led to elevated environmental concentrations and raises concerns about their toxicity to organisms and their impact on ecosystems. REE toxicity has been reported, but its precise underlying molecular effects have not been well described. Here, transcriptomic and proteomic approaches were combined to decipher the molecular responses of the model organism Saccharomyces cerevisiae to La (LREE) and Yb (HREE). Differences were observed between the early and late responses to La and Yb. Several crucial pathways were modulated in response to both REEs, such as oxidative-reduction processes, DNA replication, and carbohydrate metabolism. REE-specific responses involving the cell wall and pheromone signalling pathways were identified, and these responses have not been reported for other metals. REE exposure also modified the expression and abundance of several ion transport systems, with strong discrepancies between La and Yb. These findings are valuable for prioritizing key genes and proteins involved in La and Yb detoxification mechanisms that deserve further characterization to better understand REE environmental and human health toxicity.

Rare earth elements (REEs) are now considered emerging pollutants in the environment. Phytolacca americana, an REE hyperaccumulating plant, has been proposed for the remediation of REE-contaminated soils. However, there is no REE-related information for other Phytolacca species. Here, we examined five species (P. americana, P. acinosa, P. clavigera, P. bogotensis, and P. icosandra) for their response to REEs. REE accumulation and fractionation traits both occurred on the same order of magnitude among the five species. Heavy REEs were preferentially transferred to leaves relative to light REEs. Regardless of the species, lateral root length and chlorophyll content decreased under REE exposure, and lateral roots and foliar anthocyanins increased. However, plants did not experience or only slightly experienced oxidative stress. Finally, REE exposure strongly modulated the ionome of roots and, to a lesser extent, that of leaves, with a negative correlation between REE and Mn contents. In conclusion, our study provides new data on the response of several Phytolacca species to REEs. Moreover, we highlighted that the REE accumulation trait was conserved among Phytolacca species. Thus, we provide valuable information for the phytoremediation of REE-contaminated sites since the most appropriate Phytolacca species could be selected depending on the climatic/pedological area to be remediated.

International audience; Progressive rare earth element (REE) enrichment in aquatic environments worldwide and their resulting anthropogenic anomalies have highlighted the need for a better understanding of their biological effects, with a special emphasis on microbial cells since they play a crucial role in good ecosystem functioning. Therefore, the primary aim of this work was to achieve simultaneous characterization of the 16 REE toxicity effects on the growth kinetics of the commonly found Gram-negative bacterium E. coli (BW25113 strain). Bacterial growth curve modelling showed hormetic effects in the presence of REEs, while EC50 determination (in the mid-log phase) indicated that the four HREEs from Er to Lu in addition to Y were the most toxic metals (EC50 in the range of 8.3 to 3 µM), just after Sc (EC50 of 1.1 µM). Additional subcellular parameter assessment revealed cell membrane lipid peroxidation as well as enhanced membrane depolarization and permeability in the presence of La, Gd, or Yb as representatives of LREEs and HREEs. These subcellular effects appeared to be more intense with Gd and Yb compared with La-exposed cells, in relation to the overall higher toxicity potential reported for HREEs on bacterial growth. Also, the cellular ATP production decreased after REE exposure at their EC50. Finally, these results emphasize the importance of growth kinetic consideration as well as the complexity of REE biological effect mechanisms towards bacteria.

Environmental contextRare earth elements (REEs) are strategic metals and emerging contaminants for which plant-based remediation measures are needed. We screened a collection of hardy ferns and identified new accumulator species that preferentially transferred light REEs to their fronds. This study is an important step towards understanding the mechanisms of REE accumulation in plants. AbstractRare earth elements (REEs) include the lanthanides plus yttrium and scandium, and can be split according to their atomic mass into light (LREEs) and heavy REEs (HREEs). The increasing demand for REEs is mainly driven by new technologies, and their current low recyclability has led them to become emerging contaminants. The identification of new REE accumulators may help in determining the REE transfer mechanisms and may result in interesting candidates for phytoremediation techniques. To that end, a collection of 49 hardy fern species, grown in REE-spiked substrate, were screened for their potential in REE accumulation. REE concentrations were very low in the fronds of all Polypodium species, whereas all Athyrium species highly accumulated REEs. The REE accumulation level was more variable among the different species of Dryopteris, Blechnum, Woodwardia, Cystopteris and Polystichum. However, whatever the species, LREEs were preferentially transferred to the fronds over HREEs. This conserved trait was independent of the availability of different REEs in the substrate and instead may arise from specific transfer systems in ferns for the two groups of REEs. Furthermore, REE accumulation was correlated to Ca and Al, which suggested the existence of common uptake pathways. Altogether, these results are of great interest for phytoremediation purposes since appropriate species can be chosen according to the area to be remediated, and they also provide new insights into a more in-depth characterisation of the underlying REE accumulation mechanisms in ferns.

International audience

*Summary The Arabidopsis Yellow Stripe 1-Like (YSL) proteins have been identified by homology with the maize (Zea mays) Yellow Stripe 1 (YS1) transporter which is responsible for iron–phytosiderophore (PS) uptake by roots in response to iron shortage. Although dicotyledonous plants do not synthesize PS, they do synthesize the PS precursor nicotianamine, a strong metal chelator essential for maintenance of iron homeostasis and copper translocation. Furthermore, ZmYS1 and the rice (Oryza sativa) protein OsYSL2 have metal-nicotianamine transport activities in heterologous expression systems. In this work, we have characterized the function of AtYSL1 in planta. Two insertional loss-of-function ysl1 mutants of Arabidopsis were found to exhibit increased nicotianamine accumulation in shoots. More importantly, seeds of both ysl1 knockouts contained less iron and nicotianamine than wild-type seeds, even when produced by plants grown in the presence of an excess of iron. This phenotype could be reverted by expressing the wild-type AtYSL1 gene in ysl1 plants. ysl1 seeds germinated slowly, but this defect was rescued by an iron supply. AtYSL1 was expressed in the xylem parenchyma of leaves, where it was upregulated in response to iron excess, as well as in pollen and in young silique parts. This pattern is consistent with long-distance circulation of iron and nicotianamine and their delivery to the seed. Taken together, our work provides strong physiological evidence that iron and nicotianamine levels in seeds rely in part on AtYSL1 function.

Invited review; International audience; Background Since the identification of the genes controlling the root acquisition of iron (Fe), the control of inter- and intracellular distribution has become an important challenge in understanding metal homeostasis. The identification of the yellow stripe-like (YSL) transporter family has paved the way to decipher the mechanisms of long-distance transport of Fe. Scope Once in the plant, Fe will systematically react with organic ligands whose identity is poorly known so far. Among potential ligands, nicotianamine has been identified as an important molecule for the circulation and delivery of metals since it participates in the loading of copper (Cu) and nickel in xylem and prevents Fe precipitation in leaves. Nicotianamine is a precursor of phytosiderophores, which are high-affinity Fe ligands exclusively synthesized by Poaceae species and excreted by roots for the chelation and acquisition of Fe. Maize YS1 is the founding member of a family of membrane transporters called YS1-like (YSL), which functions in root Fe-phytosiderophore uptake from the soil. Next to this well-known Fe acquisition role, most of the other YSL family members are likely to function in plant-wide distribution of metals since (a) they are produced in vascular tissues throughout the plant and (b) they are found in non-Poaceae species that do not synthesize phytosiderophores. The hypothesized activity as Fe-nicotianamine transporters of several YSL members has been demonstrated experimentally by heterologous expression in yeast or by electrophysiology in Xenopus oocytes but, despite numerous attempts, proof of the arabidopsis YSL substrate specificity is still lacking. Reverse genetics, however, has revealed a role for AtYSL members in the remobilization of Cu and zinc from senescing leaves, in the formation of pollen and in the Fe, zinc and Cu loading of seeds. Conclusions Preliminary data on the YSL family of transporters clearly argues in favour of its role in the long-distance transport of metals through and between vascular tissues to eventually support gametogenesis and embryo development.

> Une chaude soiree d’ete... et d’un coup une petite lumiere au milieu d’un arbuste... Qui n’a jamais vu ce spectacle du ver luisant ? Ce « ver », la femelle du scarabee, Lampyris noctulica, emet une faible lumiere au niveau de son abdomen. Depuis la nuit des temps, l’homme s’emerveille de ces etres lumineux. Pourtant, ce n’est qu’en 1886 que le medecin lyonnais, Raphael Dubois, mene les premieres experiences pour decouvrir le mecanisme de la « bioluminescence » [1]. Il trouve que la reaction chimique a l’origine de cette lumiere implique seulement trois facteurs : une « luciferase » (l’enzyme), une « luciferine » (le substrat) et de l’oxygene. Cette simple reaction est retrouvee pour toute bioluminescence. Moins de 10 luciferines sont repertoriees actuellement. Ce nombre reduit de substrats contraste serieusement avec la grande diversite des luciferases [2]. Pour produire de la lumiere, chaque groupe d’organismes a, au cours de son evolution, independamment « invente » son enzyme pour produire de la lumiere. Etonnamment, il n’existe aucune conservation proteique entre ces differentes luciferases [3]. Plusieurs sequences de ces enzymes sont desormais utilisees in vivo et in vitro comme « gene rapporteur ». Ces outils sont devenus de toute premiere importance pour la biologie moderne [4]. Pour preuve, une recherche bibliographique, dans PubMed, signale plus de 18 000 publications, en 2006, pour le mot luciferase. Si le mecanisme biochimique est connu, les fonctions biologiques de ces phenomenes lumineux restent souvent enigmatiques. Sur la terre ferme, les especes bioluminescentes sont rares : deux gastropodes, quelques bacteries, champignons et vers de terre ainsi que plusieurs centaines d’insectes [5]. Les fonctions de la bioluminescence chez ces organismes sont inexpliquees hormis chez les « vers luisants », etudies en detail. Ils utilisent leur lumiere pour communiquer avec leurs congeneres. Les codes de « clignotement » sont bien connus : les femelles attirent leurs partenaires a l’aide de signaux specifiques a leur espece. Il existe meme des vers luisants « sournois » dont les femelles changent de code apres l’accouplement. Elles imitent alors le message d’une autre espece dont les mâles seront attires... vers le fond d’un estomac ! Dans les profondeurs oceaniques, le plus grand ecosysteme de notre planete (plus de 99 % de l’espace de vie et pourtant le moins etudie !), la bioluminescence est plutot la regle que l’exception [6, 7]. Plus de 90 % des organismes vivant entre 150 m et 1 500 m sont bioluminescents et on ne sait souvent pas pourquoi ! Il est suppose que cette lumiere dans l’obscurite des grands fonds pourrait servir a trois grandes fonctions : la communication, la defense et l’attaque. Certaines crevettes, par exemple, ont la capacite d’emettre une encre lumineuse soupconnee de distraire leur predateur et parfois meme d’attirer les predateurs de cet agresseur. Beaucoup de poissons des profondeurs possedent des leurres lumineux qui attirent les proies vers leur bouche dotee de dents terribles. D’autres ont des glandes sous-oculaires qui emettent des flashs de lumiere. Dans ce cas, une fonction de communication Figure 1. T. danae n’est ni lent ni mou, mais vorace et rapide quand il se jette ferocement sur l’appât. Figure 2. T. danae s’apprete a attaquer l’appât.

Rare earth elements (REEs) are strategic metals whose demand in the 21st century is increasing as a result of their essential properties useful to the fields of renewable energies, medicine, and high-technologies. They are classified as heavy REEs (HREEs), light REEs (LREEs) and non-lanthanides. Their dissemination in the environment, together with poor recyclability, leads REEs to be considered emerging contaminants, for which toxicity studies are currently very fragmented. To build a strong general foundation on the cellular and molecular response to REEs, we first adopted high-throughput and complementary strategies to study the REE stress response and their uptake in the unicellular eukaryotic model Saccharomyces cerevisiae. The deletome, transcriptome, proteome and ionome of yeast were analysed together with in-depth physiological experiments. Although common responses between REEs and other metals were highlighted, REE-specific responses were predominant. Cell wall composition, sphingolipid biosynthesis, the ESCRT pathway and endocytosis were emphasized as key elements in the cellular response to REEs. Second, we explored how REEs affect the transcriptome and ionome of the plant model Arabidopsis thaliana. REE exposure negatively affected the root architecture, as revealed by the modulation of auxin-related genes. REEs impaired the ionome, and Fe deficiency-related genes were largely represented among the most differentially expressed genes in both roots and leaves. Additionally, to identify new REE-accumulating plant models, collections of ferns and Phytolacca species were screened. Despite a conserved REE accumulation trait for Phytolacca and a few fern genera, HREE enrichment was observed in Phytolacca, while LREEs were preferentially transferred into the fronds of all fern species. However, several Dryopteris species harboured contrasting REE contents in the fronds. The latter species will be of great importance in deciphering the mechanisms of REE accumulation and tolerance. Overall, the response towards REEs differed according to their ionic radius. The cell wall composition, vacuolar detoxification, and the accumulation and fractionation of REEs notably accounted for these differences. Our findings support LREE-mediated entry through calcium channels, while new evidence was provided for the role of Fe transporters in the accumulation of HREEs. In conclusion, we have provided new insights into REE toxicity and specificities, together with the molecular elucidation of REE effects that have not previously been mechanistically explained. This work is a first multi-approach comprehensive groundwork that will be used for future studies to deepen the understanding and assessment of REE toxicity in organisms., Les terres rares (TRs) sont des métaux stratégiques du XXIe siècle dont la demande croissante résulte de leurs propriétés essentielles, notamment dans les domaines des énergies renouvelables, de la médecine et des hautes technologies. Ils sont classés en TR lourdes (HTRs), terres légères légères (LTRs) et non-lanthanides. Leur dissémination dans l'environnement, associée à une faible recyclabilité, fait des TRs des contaminants émergents pour lesquels les études de toxicité sont jusqu'à présent très disparates. Afin d’établir une base générale de la réponse cellulaire et moléculaire à un stress TRs, nous avons premièrement utilisé des stratégies complémentaires et à haut débit pour étudier la réponse, ainsi que l’absorption des TRs chez le modèle eucaryote Saccharomyces cerevisiae. Les deletome, transcriptome, protéome et ionome de la levure ont été analysés et approfondis par des analyses physiologiques ciblées. Bien que des réponses communes aux TRs et à d'autres métaux aient été mises en évidence, les réponses spécifiques aux TRs étaient prédominantes. La composition de la paroi cellulaire, la biosynthèse des sphingolipides, la voie ESCRT et l'endocytose sont des éléments clés de la réponse aux TRs. Deuxièmement, nous avons exploré les effets des TRs sur le transcriptome et le ionome du modèle végétal Arabidopsis thaliana. L'exposition des TRs a négativement impacté l'architecture racinaire, comme l'a révélé la modulation de gènes liés à l'auxine. De plus, le ionome a été modifié et les gènes liés à une carence en Fe largement représentés parmi les gènes les plus différentiellement exprimés. Afin d'identifier de nouvelles plantes modèles accumulant des TRs, des espèces de Phytolacca et de fougères ont été criblées. Malgré un trait d’accumulation des TRs conservé chez quelques genres de fougères et Phytolacca, un enrichissement en HTRs chez Phytolacca et en LTRs chez les fougères a été observé. Cependant, plusieurs espèces de Dryopteris présentent des teneurs contrastées en TRs dans les frondes et représentent de nouveaux modèles pertinents pour décrypter les mécanismes d’accumulation et de tolérance aux TRs. Globalement, des divergences ont été mises en évidence dans la réponse aux différentes TRs, en fonction de leur rayon ionique. La composition de la paroi cellulaire, la détoxification vacuolaire, mais aussi l’accumulation et le fractionnement des TRs ont souligné ces différences. Nous avons confirmé que les LTRs empruntaient les canaux calciques, tandis que de nouvelles preuves ont été données sur le rôle des transporteurs de Fe dans l'accumulation de HTRs. En conclusion, nous apportons ici de nouveaux éléments sur la toxicité et les spécificités des TRs, ainsi que des explications moléculaires pour certains effets déjà connus. Ce travail constitue un premier travail de base complet et multi-approches pour de futures études afin d’approfondir la compréhension de la toxicité des TRs chez les organismes vivants.