Three rice nicotianamine synthase genes, OsNAS1, OsNAS2 and OsNAS3 are expressed in cells involved in long-distance transport of iron and differentially regulated by iron

Abstract

Nicotianamine (NA), a chelator of metals, is ubiquitously present in plants. In graminaceous plants, NA is a biosynthetic precursor of phytosiderophores. We show that three rice NA synthase (NAS) genes are expressed in cells involved in long-distance transport and differentially regulated by Fe. OsNAS1, 2 expression were detected in Fe-sufficient roots but not in leaves, and increased markedly in both Fe-deficient roots and leaves. OsNAS3 expression was present in leaves but was very low in Fe-sufficient roots. Promoter-GUS analysis revealed that OsNAS1, 2 were expressed in companion and pericycle cells of Fe-sufficient roots. With Fe deficiency, OsNAS1, 2 expressions were extended to all root cells and were in all cells of chlorotic leaves. OsNAS3 expression was restricted to the pericycle and companion cells of the roots, and in companion cells of leaves irrespective of Fe status. These results suggested that NAS play an important role in long-distance transport of Fe.