Inoue Haruhiko, Higuchi Kyoko, Takahashi Michiko, Nakanishi Hiromi, Mori Satoshi, Nishizawa Naoko K
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Plant J. 2003 Nov;36(3):366-81. doi: 10.1046/j.1365-313x.2003.01878.x.
Nicotianamine (NA), a chelator of metals, is ubiquitously present in higher plants. In graminaceous plants, NA is a biosynthetic precursor of phytosiderophores and is thus a crucial component for iron (Fe) acquisition. Here, we show that three rice NA synthase (NAS) genes, OsNAS1, OsNAS2, and OsNAS3 are expressed in cells involved in long-distance transport of Fe and that the three genes are differentially regulated by Fe. OsNAS1 and OsNAS2 transcripts were detected in Fe-sufficient roots but not in leaves, and levels of both increased markedly in both roots and leaves in response to Fe deficiency. In contrast, the OsNAS3 transcript was present in leaves but was very low in roots of Fe-sufficient plants. Further, OsNAS3 expression was induced in roots but was suppressed in leaves in response to Fe deficiency. Promoter-GUS analysis revealed that OsNAS1 and OsNAS2 were expressed in Fe-sufficient roots in companion cells and pericycle cells adjacent to the protoxylem. With Fe deficiency, OsNAS1 and OsNAS2 expression extended to all root cells along with an increase in phytosiderophore secretion. In Fe-deficient plants, OsNAS1 and OsNAS2 were expressed in the vascular bundles of green leaves and in all cells of leaves showing severe chlorosis. 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 strongly suggested that NAS and NA play an important role in long-distance transport of Fe in rice plants, in addition to their roles in phytosiderophore secretion from roots.
烟酰胺（NA）是一种金属螯合剂，普遍存在于高等植物中。在禾本科植物中，NA是植物铁载体的生物合成前体，因此是铁（Fe）吸收的关键成分。在此，我们表明水稻的三个烟酰胺合酶（NAS）基因，即OsNAS1、OsNAS2和OsNAS3，在参与铁长距离运输的细胞中表达，并且这三个基因受铁的差异调节。在铁充足的根中检测到OsNAS1和OsNAS2的转录本，但在叶片中未检测到，并且在缺铁时，根和叶中这两个基因的水平均显著增加。相反，OsNAS3的转录本存在于叶片中，但在铁充足的植物根中非常低。此外，缺铁时OsNAS3在根中被诱导表达，但在叶片中被抑制。启动子-GUS分析表明，OsNAS1和OsNAS2在铁充足的根中，在与原生木质部相邻的伴胞和中柱鞘细胞中表达。缺铁时，OsNAS1和OsNAS2的表达扩展到所有根细胞，同时植物铁载体分泌增加。在缺铁植物中，OsNAS1和OsNAS2在绿叶的维管束以及出现严重黄化的叶片的所有细胞中表达。OsNAS3的表达局限于根的中柱鞘和伴胞，以及叶片的伴胞，与铁状态无关。这些结果有力地表明，NAS和NA除了在根分泌植物铁载体中发挥作用外，在水稻植株铁的长距离运输中也起着重要作用。
