Maize yellow stripe1 encodes a membrane protein directly involved in Fe(III) uptake

Frequently, crop plants do not take up adequate amounts of iron from the so il, leading to chlorosis, poor yield and decreased nutritional quality. Ext remely limited soil bioavailability of iron has led plants to evolve two di stinct uptake strategies: chelation, which is used by the world's principal grain crops(1,2); and reduction, which is used by other plant groups(3-5). The chelation strategy involves extrusion of low-molecular-mass secondary amino acids (mugineic acids) known as 'phytosiderophores', which chelate sp aringly soluble iron(6). The Fe(III)-phytosiderophore complex is then taken up by an unknown transporter at the root surface(7,8). The maize yellow st ripe1 (ys1) mutant is deficient in Fe(III)-phytosiderophore uptake(7-10), t herefore YS1 has been suggested to be the Fe(III)-phytosiderophore transpor ter. Here we show that ys1 is a membrane protein that mediates iron uptake. Expression of YS1 in a yeast iron uptake mutant restores growth specifical ly on Fe(III)-phytosiderophore media. Under iron-deficient conditions, ys1 messenger RNA levels increase in both roots and shoots. Cloning of ys1 is a n important step in understanding iron uptake in grasses, and has implicati ons for mechanisms controlling iron homeostasis in all plants.