Department of Biochemistry & Molecular Biology, College of Life Science, Nanjing Agriculture University, Nanjing, Jiangsu, China.
Rice Research Institute, Anhui Academy of Agricultural Sciences, Hefei, Anhui, China.
J Exp Bot. 2021 Jun 22;72(13):4839-4852. doi: 10.1093/jxb/erab159.
Vacuolar storage of iron (Fe) is important for Fe homeostasis in plants. When sufficient, excess Fe could be stored in vacuoles for remobilization in the case of Fe deficiency. Although the mechanism of Fe remobilization from vacuoles is critical for crop development under low Fe stress, the transporters that mediate vacuolar Fe translocation into the cytosol in rice remains unknown. Here, we showed that under high Fe2+ concentrations, the Δccc1 yeast mutant transformed with the rice natural resistance-associated macrophage protein 2 gene (OsNRAMP2) became more sensitive to Fe toxicity. In rice protoplasts and transgenic plants expressing Pro35S:OsNRAMP2-GFP, OsNRAMP2 was localized to the tonoplast. Vacuolar Fe content in osnramp2 knockdown lines was higher than in the wild type, while the growth of osnramp2 knockdown plants was significantly influenced by Fe deficiency. Furthermore, the germination of osnramp2 knockdown plants was arrested. Conversely, the vacuolar Fe content of Pro35S:OsNRAMP2-GFP lines was significantly lower than in the wild type, and overexpression of OsNRAMP2 increased shoot biomass under Fe deficiency. Taken together, we propose that OsNRAMP2 transports Fe from the vacuole to the cytosol and plays a pivotal role in seed germination.
液泡中铁（Fe）的储存对于植物体内的 Fe 稳态很重要。当 Fe 充足时，过量的 Fe 可以储存在液泡中，以备 Fe 缺乏时再利用。尽管液泡中 Fe 再利用的机制对于低 Fe 胁迫下的作物发育至关重要，但介导水稻液泡 Fe 向细胞质转运的转运体仍不清楚。在这里，我们表明在高 Fe2+浓度下，转化了水稻天然抗性相关巨噬细胞蛋白 2 基因（OsNRAMP2）的Δccc1 酵母突变体对 Fe 毒性更加敏感。在水稻原生质体和表达 Pro35S:OsNRAMP2-GFP 的转基因植物中，OsNRAMP2 定位于液泡膜上。osnramp2 敲低系中的液泡 Fe 含量高于野生型，而 osnramp2 敲低植物的生长受到 Fe 缺乏的显著影响。此外，osnramp2 敲低植物的发芽被阻止。相反，Pro35S:OsNRAMP2-GFP 系的液泡 Fe 含量明显低于野生型，过表达 OsNRAMP2 增加了 Fe 缺乏下的地上生物量。综上所述，我们提出 OsNRAMP2 将 Fe 从液泡转运到细胞质，在种子发芽中发挥关键作用。
