Institute of Botany, Heinrich-Heine University, D-40225 Düsseldorf, Germany.
Former address: Department of Biosciences-Plant Biology, Saarland University, D-66123 Saarbrücken, Germany.
Plant Physiol. 2019 Jul;180(3):1564-1581. doi: 10.1104/pp.19.00163. Epub 2019 Apr 30.
Iron is a key transition element in the biosphere and is crucial for living organisms, although its cellular excess can be deleterious. Maintaining the balance of optimal iron availability in the model plant Arabidopsis () requires the precise operation of iron import through the principal iron transporter IRON-REGULATED TRANSPORTER1 (IRT1). Targeted inhibition of IRT1 can prevent oxidative stress, thus promoting plant survival. Here, we report the identification of an IRT1 inhibitor, namely the C2 domain-containing peripheral membrane protein ENHANCED BENDING1 (EHB1). EHB1 interacts with the cytoplasmically exposed variable region of IRT1, and we demonstrate that this interaction is greatly promoted by the presence of calcium. We found that EHB1 binds lipids characteristic of the plasma membrane, and the interaction between EHB1 and plant membranes is calcium-dependent. Molecular simulations showed that EHB1 membrane binding is a two-step process that precedes the interaction between EHB1 and IRT1. Genetic and physiological analyses indicated that EHB1 acts as a negative regulator of iron acquisition. The presence of EHB1 prevented the IRT1-mediated complementation of iron-deficient yeast (). Our data suggest that EHB1 acts as a direct inhibitor of IRT1-mediated iron import into the cell. These findings represent a major step in understanding plant iron acquisition, a process that underlies the primary production of bioavailable iron for land ecosystems.
铁是生物圈中的一种关键过渡元素，对生物体至关重要，尽管其细胞过量可能是有害的。维持模式植物拟南芥（）中最佳铁可用性的平衡需要通过主要铁转运蛋白铁调节转运蛋白 1（IRT1）精确地进行铁导入。靶向抑制 IRT1 可以防止氧化应激，从而促进植物存活。在这里，我们报告了一种 IRT1 抑制剂的鉴定，即含有 C2 结构域的外周膜蛋白增强弯曲 1（EHB1）。EHB1 与 IRT1 细胞质暴露的可变区域相互作用，我们证明钙的存在大大促进了这种相互作用。我们发现 EHB1 结合质膜特征性的脂质，并且 EHB1 与植物膜之间的相互作用是钙依赖性的。分子模拟表明，EHB1 膜结合是一个两步过程，先于 EHB1 和 IRT1 之间的相互作用。遗传和生理分析表明，EHB1 作为铁获取的负调节剂起作用。EHB1 的存在阻止了 IRT1 介导的缺铁酵母（）的互补。我们的数据表明，EHB1 作为 IRT1 介导的铁进入细胞的直接抑制剂发挥作用。这些发现代表了理解植物铁获取的重要一步，这是陆地生态系统生物可利用铁的主要初级生产过程的基础。
