Maize ZmFDR3 localized in chloroplasts is involved in iron transport

Iron is an essential nutrient for plant metabolism such that Fe-limited plants display chlorosis and suffer from reduced photosynthetic efficiency. Differential display previously identified genes whose expression was elevated in Fe-deficient maize roots. Here, we describe the functional characterization of one of the genes identified in the screen, ZmFDR3 (Zea maize Fe-deficiency-related). Heterologous functional complementation assays using a yeast iron uptake mutant showed that ZmFDR3 functions in iron transport. ZmFDR3 contains a domain found in FliN-proteins of the type III secretion system and is predicted to localize to the thylakoid of plastids. Fluorescence immunocytochemistry showed that ZmFDR3 is localized in the plastids of roots, stems and leaves, with high expression found in guard cell chloroplasts. Transgenic tobacco expressing a 35S-ZmFDR3 construct contains elevated iron content, displays well arranged thylakoid membranes and has photosynthetic indices that are higher than those of the wild type. Together, these results suggest that ZmFDR3 functions in chloroplast iron transport.