Rare earth element hyperaccumulation in vascular plants: Occurrence, mechanisms, and applications

The hyperaccumulation of rare earth elements (REEs) is an unusual natural ability of certain plant species to accumulate these elements at concentrations hundreds or even thousands of times higher than those typically found in most plant species. Although substantial progress has been made in understanding the mechanisms underlying transition metals hyperaccumulation, the specific pathways involved in REE hyperaccumulation remain poorly understood. Here we synthesize current advances and systematically dissect four critical phases involved in REE hyperaccumulation: rhizosphere mobilization, root uptake and xylem loading, xylem transport, and leaf detoxification. We show that root exudates are essential for rhizosphere mobilization, and that cell walls and/or silicon play pivotal roles in leaf REE detoxification, mechanisms markedly distinct from those underlying the hyperaccumulation of other trace metals. We further investigate interspecies divergence in REE accumulation and fractionation patterns, examining the geochemical and biochemical drivers that govern the transfer efficiencies of light REEs (LREEs) and heavy REEs (HREEs) from soil to plants. Current knowledge gaps are critically evaluated, with particular emphasis on how emerging technologies and multidisciplinary approaches can decode the transport dynamics and evolutionary drivers of REE hyperaccumulation. This synthesis constructs a roadmap for deepening molecular-, physiological-, and biochemical-level understanding of REE hyperaccumulation and for advancing agromining as an innovative route to recover REEs from unconventional sources.