Efflux transporter of mugineic acid family phytosiderophores

Abstract

Iron is essential for the survival and proliferation of all plants.　Higher plants have developed two distinct strategies to acquire iron, which is only slightly soluble, from the rhizosphere: the reduction strategy of nongraminaceous plants and the chelation strategy of graminaceous plants.　Graminaceous plants secrete mugineic acid family phytosiderophores, which solubilise iron in the soil, and then take up the resulting iron-phytosiderophore complexes.　Although phytosiderophore secretion is crucial for plant growth, its molecular mechanism remained unknown.　We showed that the efflux of deoxymugineic acid, the primary phytosiderophore from rice, barley and maize, involves the TOM1, HvTOM1 and ZmTOM1 genes, respectively.　Our identification of phytosiderophore efflux transporters has revealed the final piece in the molecular machinery of iron acquisition in graminaceous plants.　Furthermore, we showed that the TOM2, one of the rice homologues of TOM1, is involved in the internal transport of deoxymugineic acid, which is required for normal plant growth.　We have also identified ENA1 and ENA2, genes encoding efflux transporters of nicotianamine, a chelater of metals and an essential intermediate in the production of deoxymugineic acid.