Some gramineous plants such as barley and wheat have a distinct strategy (Strategy II) for iron (Fe) acquisition, which is different from non-grass species. Iron acquisition by gramineous plants includes 1) biosynthesis of phytosiderophores (mugineic acids) inside the roots; 2) secretion of phytosiderophores to the rhizosphere; 3) solubilization of insoluble iron in soils by chelation of phytosiderophores, and 4) uptake of the ferric-phytosiderophore complex by the roots. We have been working on biosynthetic pathway of various phytosiderophores in different plant species and uptake system. Recently, we have identified a transporter for the ferric-phytosiderophore complex (Plant J. 46: 563-572, 2006). It is greatly up-regulated by iron-deficiency and localized at the epidermal cells.
Furthermore, we recently identified a transporter, OsFRDL1, which is required for efficient translocation of iron from the roots to shoots in rice (Plant Physiol. 149: 297-305C2009). This is a citrate transporter and localized at the pericycle cells. Knockout of this gene result in Fe precipitation in the roots and chlorosis in the leaves.