Only a very small number of plant species, i.e., hyperaccumulators, can assimilate >1000 mg kg-1 rare earth element (REEs) in the shoots, which are 2-3 orders than that of the normal plants. The exploration of the underlying mechanisms controlling the REEs uptake and accumulation in these hyperaccumulators thus attracts extensive attention worldwide. In the past 10 years, our team has been trying to gain a deep understanding of the fate of REEs in the soil-hyperaccumulator plant system, by integrating knowledge from soil science, plant physiology, molecular biology, ecology and so on. In the soil-root interface, we found that P-deficiency induced rhizosphere acidification and small organic acids exudation play an critical role in soil REEs releasing and activation, and subsequent leaf REEs hyperaccumulation. During the uptake process, we found that Al/Ca/Mn pathways may involve in REE root uptake; we also identified a root-based transporter NREET1 from NRAMP family in the hyperaccumulator plant Dicranopteris linearis (the best-known light REEs hyperaccumulator species). 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-growing D. linearis. During the root-to-shoot translocation in Phytolacca americana (the only-known heavy REEs hyperaccumulator species), small organic acids facilitate the long-distance transport of REEs, especially the heavy REEs, playing a role in the preferential accumulation of heavy REEs in its leaves. In D. linearis shoot, the REEs were co-localized with Si, and mostly concentrated in the bio-inactive tissues, e.g., necrotic lesions, veins, and the epidermis. Moreover, Si can mitigate REE stress through the formation of [Si-cell wall] matrix, which might be the key for D. linearis to tolerate excessive REEs in leaves. These results provide insights on how hyperaccumulator species efficiently assimilate and tolerant high concentration of REEs in the shoot, and this knowledge is useful for developing phytotechnological applications (such as REE phytomining) in REE-contaminated sites or soils naturally rich in REEs.

稀土,超富集植物,根际活化,跨膜蛋白,区隔化