OsELP Mediated Apoplastic Sequestration in Roots Acts as an Arsenic Filter, Limiting Grain Accumulation in Rice.

Arsenic (As) contamination in rice (Oryza sativa L.) is a persistent threat to global food safety. Expansin-like proteins have been implicated in cell wall dynamics and metal binding; however, their in planta role in As detoxification remains unexplored. This study reveals a pivotal role for the rice expansin-like protein OsELP in As compartmentalisation and tolerance. Using transgenic approaches in Arabidopsis thaliana and rice, we showed that OsELP overexpression significantly enhanced tolerance to both arsenite and arsenate stress, protecting biomass and photosynthetic efficiency. Mechanistically, OsELP facilitated the apoplastic sequestration of As in roots, as visualised by Scanning Electron Microscopy-Energy Dispersive x-ray spectroscopy (SEM-EDX) imaging. This sequestration acted as a root filter, increasing root As retention and reducing shoot translocation, which culminated in a significant reduction of As in grains in the overexpression lines. This spatial restriction of As mitigated oxidative and photosynthetic damage by enhancing antioxidant enzyme activities and limiting reactive oxygen species accumulation. In contrast, the Oselp knockout line exhibited increased As accumulation in aerial tissues and heightened sensitivity. This study reveals a previously uncharacterised functional link between cell wall-associated expansin-like proteins and As mobility regulation, highlighting OsELP as a promising genetic target for developing low-As rice cultivars.