Zhang Xiu-Yue, Zhang Xi, Zhang Qi, Pan Xiao-Xi, Yan Luo-Chen, Ma Xiao-Juan, Zhao Wei-Zhong, Qi Xiao-Ting, Yin Li-Ping
College of Life Sciences, Capital Normal University, No. 105 Xisanhuan North Street, Haidian District, Beijing, 100048, China.
Institute of Mathematics and Interdisciplinary Sciences, Capital Normal University, No. 105 Xisanhuan North Street, Haidian District, Beijing, 100048, China.
Plant J. 2017 Apr;90(1):147-163. doi: 10.1111/tpj.13482.
Iron (Fe)-homeostasis in the plastids is closely associated with Fe transport proteins that prevent Fe from occurring in its toxic free ionic forms. However, the number of known protein families related to Fe transport in the plastids (about five) and the function of iron in non-green plastids is limited. In the present study, we report the functional characterization of Zea mays Fe deficiency-related 4 (ZmFDR4), which was isolated from a differentially expressed clone of a cDNA library of Fe deficiency-induced maize roots. ZmFDR4 is homologous to the bacterial FliP superfamily, coexisted in both algae and terrestrial plants, and capable of restoring the normal growth of the yeast mutant fet3fet4, which possesses defective Fe uptake systems. ZmFDR4 mRNA is ubiquitous in maize and is inducible by iron deficiency in wheat. Transient expression of the 35S:ZmFDR4-eGFP fusion protein in rice protoplasts indicated that ZmFDR4 maybe localizes to the plastids envelope and thylakoid. In 35S:c-Myc-ZmFDR4 transgenic tobacco, immunohistochemistry and immunoblotting confirmed that ZmFDR4 is targeted to both the chloroplast envelope and thylakoid. Meanwhile, ultrastructure analysis indicates that ZmFDR4 promotes the density of plastids and accumulation of starch grains. Moreover, Bathophenanthroline disulfonate (BPDS) colorimetry and inductively coupled plasma mass spectrometry (ICP-MS) indicate that ZmFDR4 is related to Fe uptake by plastids and increases seed Fe content. Finally, 35S:c-Myc-ZmFDR4 transgenic tobacco show enhanced photosynthetic efficiency. Therefore, the results of the present study demonstrate that ZmFDR4 functions as an iron transporter in monocot plastids and provide insight into the process of Fe uptake by plastids.
质体中的铁（Fe）稳态与防止铁以有毒的游离离子形式存在的铁转运蛋白密切相关。然而，已知与质体中铁转运相关的蛋白家族数量（约5个）以及铁在非绿色质体中的功能是有限的。在本研究中，我们报道了玉米缺铁相关4（ZmFDR4）的功能特性，它是从缺铁诱导的玉米根cDNA文库的差异表达克隆中分离出来的。ZmFDR4与细菌FliP超家族同源，存在于藻类和陆生植物中，并且能够恢复具有缺陷铁摄取系统的酵母突变体fet3fet4的正常生长。ZmFDR4 mRNA在玉米中普遍存在，并且在小麦中可被缺铁诱导。35S:ZmFDR4-eGFP融合蛋白在水稻原生质体中的瞬时表达表明ZmFDR4可能定位于质体包膜和类囊体。在35S:c-Myc-ZmFDR4转基因烟草中，免疫组织化学和免疫印迹证实ZmFDR4靶向叶绿体包膜和类囊体。同时，超微结构分析表明ZmFDR4促进质体密度和淀粉粒积累。此外，二磺酸邻菲罗啉（BPDS）比色法和电感耦合等离子体质谱（ICP-MS）表明ZmFDR4与质体对铁的摄取有关，并增加种子铁含量。最后，35S:c-Myc-ZmFDR4转基因烟草显示出光合效率增强。因此，本研究结果表明ZmFDR4在单子叶植物质体中作为铁转运蛋白发挥作用，并为质体摄取铁过程提供了见解。
