The OsNramp4 aluminum transporter is involved in cadmium accumulation in rice grains

Cadmium (Cd) toxicity affects many crops. Members of the OsNramp (Natural resistance-associated macrophage protein) gene family play important roles in the transport of divalent or trivalent cations in rice (Oryza sativa L.). This study explored a possible involvement of OsNramp4 in Cd²⁺ transport in rice. We employed the CRISPR/cas9 technique to obtain rice OsNramp4 knockout lines. Using NMT (Non-invasive Micro-test Technology) system for real-time measurement, it was found that the net Cd²⁺ flux was significantly lower than that of wild-type. The yeast strain expressing OsNramp4 grew poorly under Cd²⁺ stress, and accumulated more Cd²⁺ than the control strain, which enhanced the sensitivity of yeast to Cd²⁺. OsNramp4 was membrane-localized and mainly expressed in roots, but after tillering, its expression shifted to the nodes and glumes. Furthermore, the loss-of-function OsNramp4 mutation lowered the root cell sap Cd²⁺ content, resulting in a significant decrease in Cd²⁺ content in shoot and Cd²⁺ accumulation in grains. We characterized the OsNramp4, an Al³⁺ transporter with the ability to alter the cellular distribution of Cd²⁺ in rice and to reduce Cd²⁺ content in the grain. Our study highlights the complexity of ion uptake and transport in plants.