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Rare earth elements (REEs) are critical for numerous modern technologies, and demand is increasing globally; however,production steps are resource-intensive and environmentally damaging.Some plant species are able to hyper accumulate REEs, and understanding the biology behind this phenomenon could play a pivotal role in developing more environmentally friendly REE recovery technologies. Here, we identified a REE transporter NRAMP REE Transporter 1 (NREET1)from the REE hyper accumulator fern Dicranopteris linearis. AlthoughNREET1 belongs to the natural resistance-associated macrophage protein(NRAMP) family, it shares a low similarity with other NRAMP members.When expressed in yeast, NREET1 exhibited REE transport capacity, but itcould not transport divalent metals, such as zinc, nickel, manganese, or iron.NREET1 is mainly expressed in D. linearis roots and predominantly localized in the plasma membrane. Expression studies in Arabidopsis thaliana revealed that NREET1 functions as a transporter mediating REE uptake and transfer from root cell walls into the cytoplasm. Moreover, NREET1 has a higher affinity for transporting light REEs compared to heavy REEs, which is consistent to the preferential enrichment of light REEs in field-grown D. linearis. We therefore conclude that NREET1 may play an important role in the uptake and consequently hyper accumulation of REEs in D.linearis. These findings lay the foundation for the use of synthetic biology techniques to design and produce sustainable, plant-based REE recovery systems.

An increasing number of studies have shown how feedback interactions between plants and soil can influence primary and secondary succession. However, very little is known about the patterns and mechanisms of such plant-soil feedbacks on stressed mine tailings ecosystem, which can be severely contaminated by a range of toxic elements. In a two-phase plant-soil feedback experiment based on the rare earth element (REE) mine tailing soil, we investigated biotic (changes in bacterial and fungal community) and abiotic legacies (changes in chemical properties) of three pioneer grass species, and examined feedback effects of three grasses, two legumes and two woody plants with different root traits. Positive plant-soil feedback was found in Miscanthus sinensis, Paspalum thunbergii and Tephrosia candida, and neutral feedback was observed in other four plants. These effects corresponded with an increase of nutrients and total organic carbon, as well as a decrease of acidity and extractable aluminum and REEs. There were less signs of biotic changes in the conditioned tailings. The correlation analysis suggested a relationship between responses to soil legacies and root traits, as well as root economics spectrum. On the mine tailings, acquisitive species with higher specific root length appeared to have greater potential for positive feedback. Synthesis and application: Our study shows that early succession on contaminated REE mine tailings may lead to more positive plant-soil feedback than predicted based on results of non-contaminated soils, mainly due to the alleviation of abiotic stress in tailings. Therefore, the improvement of specific abiotic soil stress and the trait-based selection of acquisitive plants should be preferentially considered to promote the primary restoration of degraded land., An increasing number of studies have shown how feedback interactions between plants and soil can influence primary and secondary succession. However, very little is known about the patterns and mechanisms of such plant-soil feedbacks on stressed mine tailings ecosystem, which can be severely contaminated by a range of toxic elements. In a two-phase plant-soil feedback experiment based on the rare earth element (REE) mine tailing soil, we investigated biotic (changes in bacterial and fungal community) and abiotic legacies (changes in chemical properties) of three pioneer grass species, and examined feedback effects of three grasses, two legumes and two woody plants with different root traits. Positive plant-soil feedback was found in Miscanthus sinensis, Paspalum thunbergii and Tephrosia candida, and neutral feedback was observed in other four plants. These effects corresponded with an increase of nutrients and total organic carbon, as well as a decrease of acidity and extractable aluminum and REEs. There were less signs of biotic changes in the conditioned tailings. The correlation analysis suggested a relationship between responses to soil legacies and root traits, as well as root economics spectrum. On the mine tailings, acquisitive species with higher specific root length appeared to have greater potential for positive feedback. Synthesis and application: Our study shows that early succession on contaminated REE mine tailings may lead to more positive plant-soil feedback than predicted based on results of non-contaminated soils, mainly due to the alleviation of abiotic stress in tailings. Therefore, the improvement of specific abiotic soil stress and the trait-based selection of acquisitive plants should be preferentially considered to promote the primary restoration of degraded land.