Genome-edited rice variety with low-cadmium accumulation in the grain

Cadmium (Cd) is a toxic and carcinogenic heavy metal, and rice, as a staple food, is a major source of dietary Cd intake. Therefore, limiting the transfer of Cd from soil to rice grain without compromising grain yield is a critical issue for human health. In this study, through base-editing-mediated mutagenesis screening targeting OsNramp5, a major transporter gene for manganese (Mn) and Cd uptake, we identified a single amino acid substitution at position 441 (Ile to Thr) that significantly reduced Cd accumulation in both shoots and grains without affecting the accumulation of other essential metals. Functional analysis revealed that this point mutation did not alter gene expression, protein abundance, subcellular localization, or Cd and Mn transport activity in yeast. However, we found that OsNramp5 also transports zinc (Zn), and the point mutation increased its selectivity for Zn. It is likely that elevated Zn levels in root cells competitively inhibit Cd release into the xylem, thereby reducing root-to-shoot Cd translocation. A field trial confirmed that the mutated OsNramp5 did not affect grain yield or essential micronutrient concentration but significantly decreased Cd accumulation in grains. Our findings suggest that precise editing of this key residue in OsNramp5 offers an effective strategy to reduce Cd transfer from soil to rice grain without yield penalty.