Institute for Integrative Biology of the Cell (I2BC), CNRS/CEA/Univ. Paris Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette, France.
Institute for Integrative Biology of the Cell (I2BC), CNRS/CEA/Univ. Paris Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette, France.
Mol Cell. 2018 Mar 15;69(6):953-964.e5. doi: 10.1016/j.molcel.2018.02.009.
Plant roots forage the soil for iron, the concentration of which can be dramatically lower than those needed for growth. Soil iron uptake uses the broad metal spectrum IRT1 transporter that also transports zinc, manganese, cobalt, and cadmium. Sophisticated iron-dependent transcriptional regulatory mechanisms allow plants to tightly control the abundance of IRT1, ensuring optimal absorption of iron. Here, we uncover that IRT1 acts as a transporter and receptor (transceptor), directly sensing excess of its non-iron metal substrates in the cytoplasm, to regulate its own degradation. Direct metal binding to a histidine-rich stretch in IRT1 triggers its phosphorylation by the CIPK23 kinase and facilitates the subsequent recruitment of the IDF1 E3 ligase. CIPK23-driven phosphorylation and IDF1-mediated lysine-63 polyubiquitination are jointly required for efficient endosomal sorting and vacuolar degradation of IRT1. Thus, IRT1 directly senses elevated non-iron metal concentrations and integrates multiple substrate-dependent regulations to optimize iron uptake and protect plants from highly reactive metals.
植物根系从土壤中获取铁，而土壤中铁的浓度往往远低于植物生长所需的浓度。植物通过广谱的金属转运体 IRT1 来吸收铁，该转运体同时也能转运锌、锰、钴和镉。复杂的铁依赖性转录调控机制使植物能够严格控制 IRT1 的丰度，从而确保铁的最佳吸收。在这里，我们发现 IRT1 作为一种转运体和受体（转受体），能够直接在细胞质中感应其非铁金属底物的过量，并调节自身的降解。IRT1 中的一个富含组氨酸的结构域与金属直接结合，触发 CIPK23 激酶对其进行磷酸化，随后促进 IDF1 E3 连接酶的募集。CIPK23 驱动的磷酸化和 IDF1 介导的赖氨酸-63 多泛素化共同促进 IRT1 的内体分拣和液泡降解。因此，IRT1 能够直接感应升高的非铁金属浓度，并整合多种底物依赖性调控，以优化铁的吸收并保护植物免受高反应性金属的侵害。
