The Phytosiderophore Efflux Transporter TOM2 Is Involved in Metal Transport in Rice
The Phytosiderophore Efflux Transporter TOM2 Is Involved in Metal Transport in Rice
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DOI：
10.1074/jbc.m114.635193
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发表时间：
2015-11-13
影响因子：
4.8
通讯作者：
Nishizawa, Naoko K.
中科院分区：
文献类型：
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作者：
Nozoye, Tomoko;Nagasaka, Seiji;Nishizawa, Naoko K.
铁是所有生物体必需的金属元素。禾本科植物从根部产生并分泌麦根酸家族植物铁载体以获取土壤中的铁。植物铁载体螯合并溶解土壤中不溶性氢氧化铁。随后，植物通过根细胞膜上的特定转运蛋白吸收铁-植物铁载体复合物。植物铁载体也被认为对于包括铁在内的各种过渡金属的内部运输很重要。在本研究中，我们分析了 TOM2 和 TOM3，它们是麦根酸家族植物铁载体 1 (TOM1) 转运蛋白的水稻同源物，TOM1 是直接参与植物铁载体分泌到土壤中的关键外排转运蛋白。使用启动子-β-葡萄糖醛酸酶的转基因水稻分析表明，TOM2 在涉及金属易位的组织中表达，而 TOM3 仅在植物的有限部分中表达。在种子成熟和发芽过程中，在发育组织中观察到强烈的 TOM2 表达，而在种子成熟过程中 TOM3 表达较弱。与非转化体和 TOM3 抑制的水稻相比，TOM2 表达受到 RNA 干扰抑制的转基因水稻显示出生长缺陷。表达 TOM2 的非洲爪蟾卵母细胞释放 C-14 标记的脱氧麦根酸，这是水稻生物合成途径中的初始植物铁载体化合物。在洋葱表皮和水稻根细胞中，TOM2-GFP融合蛋白定位于细胞膜，表明TOM2蛋白是植物铁载体流出至细胞外部的转运蛋白。我们的结果表明，TOM2 参与正常植物生长所需的脱氧麦根酸的内部运输。
Iron is an essential metal element for all living organisms. Graminaceous plants produce and secrete mugineic acid family phytosiderophores from their roots to acquire iron in the soil. Phytosiderophores chelate and solubilize insoluble iron hydroxide in the soil. Subsequently, plants take up iron-phytosiderophore complexes through specific transporters on the root cell membrane. Phytosiderophores are also thought to be important for the internal transport of various transition metals, including iron. In this study, we analyzed TOM2 and TOM3, rice homologs of transporter of mugineic acid family phytosiderophores 1 (TOM1), a crucial efflux transporter directly involved in phytosiderophore secretion into the soil. Transgenic rice analysis using promoter-beta-glucuronidase revealed that TOM2 was expressed in tissues involved in metal translocation, whereas TOM3 was expressed only in restricted parts of the plant. Strong TOM2 expression was observed in developing tissues during seed maturation and germination, whereas TOM3 expression was weak during seed maturation. Transgenic rice in which TOM2 expression was repressed by RNA interference showed growth defects compared with non-transformants and TOM3-repressed rice. Xenopus laevis oocytes expressing TOM2 released C-14-labeled deoxymugineic acid, the initial phytosiderophore compound in the biosynthetic pathway in rice. In onion epidermal and rice root cells, the TOM2-GFP fusion protein localized to the cell membrane, indicating that the TOM2 protein is a transporter for phytosiderophore efflux to the cell exterior. Our results indicate that TOM2 is involved in the internal transport of deoxymugineic acid, which is required for normal plant growth.