A node-localized efflux transporter for loading iron to developing tissues in rice

Iron (Fe) is an essential micronutrient for plant growth and development. It plays crucial roles in various organs and tissues of plants, but the molecular mechanisms governing its distribution to the above-ground parts after root uptake remain unclear. In this study, we identify OsIET1 (Oryza sativa Iron Efflux Transporter 1), a rice gene highly expressed in the nodes. OsIET1 encodes a plasma membrane-localized protein, which shows efflux transport activity for ferrous iron. It is predominantly expressed in the xylem regions of diffuse vascular bundles, and its expression is upregulated under high Fe conditions. Disruption of OsIET1 impairs Fe allocation, reducing Fe transport to developing tissues (young leaves and grains), while increasing accumulation in nodes and older leaves. This misdistribution causes chlorosis in young leaves and decreases grain yield, especially under Fe-deficient conditions. Furthermore, we detect excessive Fe deposition around the xylem of diffuse vascular bundles in the nodes. Given the pivotal role of nodes in mineral distribution, our results indicate that OsIET1 mediates inter-vascular Fe transfer by facilitating Fe loading into the xylem of diffuse vascular bundles. This process ensures preferential Fe delivery to developing tissues, thereby promoting optimal plant growth and productivity.