Mizuno Daichi, Higuchi Kyoko, Sakamoto Tatsuya, Nakanishi Hiromi, Mori Satoshi, Nishizawa Naoko K
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Science, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Plant Physiol. 2003 Aug;132(4):1989-97. doi: 10.1104/pp.102.019869.
Nicotianamine synthase (NAS) is an enzyme that is critical for the biosynthesis of the mugineic acid family of phytosiderophores in graminaceous plants, and for the homeostasis of metal ions in nongraminaceous plants. We isolated one genomic NAS clone, ZmNAS3, and two cDNA NAS clones, ZmNAS1 and ZmNAS2, from maize (Zea mays cv Alice). In agreement with the increased secretion of phytosiderophores with Fe deficiency, ZmNAS1 and ZmNAS2 were positively expressed only in Fe-deficient roots. In contrast, ZmNAS3 was expressed under Fe-sufficient conditions, and was negatively regulated by Fe deficiency. This is the first report describing down-regulation of NAS gene expression in response to Fe deficiency in plants, shedding light on the role of nicotianamine in graminaceous plants, other than as a precursor in phytosiderophore production. ZmNAS1-green fluorescent protein (sGFP) and ZmNAS2-sGFP were localized at spots in the cytoplasm of onion (Allium cepa) epidermal cells, whereas ZmNAS3-sGFP was distributed throughout the cytoplasm of these cells. ZmNAS1 and ZmNAS3 showed NAS activity in vitro, whereas ZmNAS2 showed none. Due to its duplicated structure, ZmNAS2 was much larger (65.8 kD) than ZmNAS1, ZmNAS3, and previously characterized NAS proteins (30-38 kD) from other plant species. We reveal that maize has two types of NAS proteins based on their expression pattern and subcellular localization.
烟酰胺合酶（NAS）是一种对禾本科植物中 mugineic 酸家族植物铁载体的生物合成以及非禾本科植物中金属离子的稳态至关重要的酶。我们从玉米（Zea mays cv Alice）中分离出一个基因组 NAS 克隆 ZmNAS3 和两个 cDNA NAS 克隆 ZmNAS1 和 ZmNAS2。与缺铁时植物铁载体分泌增加一致，ZmNAS1 和 ZmNAS2 仅在缺铁的根中呈阳性表达。相比之下，ZmNAS3 在铁充足的条件下表达，并且受缺铁的负调控。这是第一份描述植物中 NAS 基因表达因缺铁而下调的报告，揭示了烟酰胺在禾本科植物中的作用，而不仅仅是作为植物铁载体产生的前体。ZmNAS1-绿色荧光蛋白（sGFP）和 ZmNAS2-sGFP 定位于洋葱（Allium cepa）表皮细胞细胞质中的斑点处，而 ZmNAS3-sGFP 分布于这些细胞的整个细胞质中。ZmNAS1 和 ZmNAS3 在体外显示出 NAS 活性，而 ZmNAS2 则没有。由于其重复结构，ZmNAS2 比 ZmNAS1、ZmNAS3 以及先前鉴定的来自其他植物物种的 NAS 蛋白（30 - 38 kD）大得多（65.8 kD）。我们发现，基于它们的表达模式和亚细胞定位，玉米有两种类型的 NAS 蛋白。
