Institute for Integrative Biology of the Cell, Unité Mixte de Recherche 9198, Centre National de la Recherche Scientifique/Commissariat à l'Énergie Atomique et aux Énergies Alternatives/Université Paris Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette, France.
Plant Science Research Laboratory, Unité Mixte de Recherche 5546, Centre National de la Recherche Scientifique/University of Toulouse 3, 31320 Auzeville Tolosane, France.
Plant Physiol. 2020 Nov;184(3):1236-1250. doi: 10.1104/pp.20.00234. Epub 2020 Sep 1.
In plants, iron uptake from the soil is tightly regulated to ensure optimal growth and development. Iron absorption in Arabidopsis root epidermal cells requires the IRT1 transporter that also allows the entry of certain non-iron metals, such as Zn, Mn, and Co. Recent work demonstrated that IRT1 endocytosis and degradation are controlled by IRT1 non-iron metal substrates in a ubiquitin-dependent manner. To better understand how metal uptake is regulated, we identified IRT1-interacting proteins in Arabidopsis roots by mass spectrometry and established an interactome of IRT1. Interestingly, the AHA2 proton pump and the FRO2 reductase, both of which work in concert with IRT1 in the acidification-reduction-transport strategy of iron uptake, were part of this interactome. We confirmed that IRT1, FRO2, and AHA2 associate through co-immunopurification and split-ubiquitin analyses, and uncovered that they form tripartite direct interactions. We characterized the dynamics of the iron uptake complex and showed that FRO2 and AHA2 ubiquitination is independent of the non-iron metal substrates transported by IRT1. In addition, FRO2 and AHA2 are not largely endocytosed in response to non-iron metal excess, unlike IRT1. Indeed, we provide evidence that the phosphorylation of IRT1 in response to high levels of non-iron metals likely triggers dissociation of the complex. Overall, we propose that a dedicated iron-acquisition protein complex exists at the cell surface of Arabidopsis root epidermal cells to optimize iron uptake.
在植物中，从土壤中摄取铁受到严格调控，以确保最佳的生长和发育。拟南芥根表皮细胞中的铁吸收需要 IRT1 转运蛋白，该蛋白也允许某些非铁金属，如锌、锰和钴进入。最近的工作表明，IRT1 的内吞作用和降解受 IRT1 非铁金属底物的泛素依赖性控制。为了更好地理解金属摄取是如何被调控的，我们通过质谱法鉴定了拟南芥根中的 IRT1 相互作用蛋白，并建立了 IRT1 相互作用组。有趣的是，AHA2 质子泵和 FRO2 还原酶，这两者都与 IRT1 在铁摄取的酸化-还原-转运策略中协同作用，是这个相互作用组的一部分。我们证实 IRT1、FRO2 和 AHA2 通过共免疫沉淀和分裂泛素分析相互关联，并发现它们形成了三元直接相互作用。我们还对铁摄取复合物的动力学进行了表征，并表明 FRO2 和 AHA2 的泛素化与 IRT1 转运的非铁金属底物无关。此外，与 IRT1 不同，FRO2 和 AHA2 不会因非铁金属过量而大量内吞。事实上，我们提供的证据表明，IRT1 对高水平非铁金属的磷酸化可能会触发复合物的解离。总的来说，我们提出在拟南芥根表皮细胞的细胞表面存在一个专门的铁获取蛋白复合物，以优化铁的摄取。
