Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, Provincial Key Laboratory of Biotechnology, College of Life Sciences, Northwest University, Xi'an 710069, China; Institute of Future Agriculture, Northwest Agriculture and Forestry University, Yangling, Shaanxi 712100, China.
School of Life Sciences, Nanjing University, Nanjing, Jiangsu 210023, China.
Mol Plant. 2022 Oct 3;15(10):1590-1601. doi: 10.1016/j.molp.2022.09.005. Epub 2022 Sep 12.
Excess phosphate (Pi) is stored into the vacuole through Pi transporters so that cytoplasmic Pi levels remain stable in plant cells. We hypothesized that the vacuolar Pi transporters may harbor a Pi-sensing mechanism so that they are activated to deliver Pi into the vacuole only when cytosolic Pi reaches a threshold high level. We tested this hypothesis using Vacuolar Phosphate Transporter 1 (VPT1), a SPX domain-containing vacuolar Pi transporter, as a model. Recent studies have defined SPX as a Pi-sensing module that binds inositol polyphosphate signaling molecules (InsPs) produced at high cellular Pi status. We showed here that Pi-deficient conditions or mutation of the SPX domain severely impaired the transport activity of VPT1. We further identified an auto-inhibitory domain in VPT1 that suppresses its transport activity. Taking together the results from detailed structure-function analyses, our study suggests that VPT1 is in the auto-inhibitory state when Pi status is low, whereas at high cellular Pi status InsPs are produced and bind SPX domain to switch on VPT1 activity to deliver Pi into the vacuole. This thus provides an auto-regulatory mechanism for VPT1-mediated Pi sensing and homeostasis in plant cells.
过量的磷酸盐 (Pi) 通过 Pi 转运蛋白储存在液泡中，以使细胞质 Pi 水平在植物细胞中保持稳定。我们假设液泡 Pi 转运蛋白可能具有 Pi 感应机制，因此只有当细胞质 Pi 达到高阈值水平时，它们才会被激活将 Pi 输送到液泡中。我们使用液泡磷酸盐转运蛋白 1 (VPT1) 作为模型来验证这一假设，VPT1 是一种含有 SPX 结构域的液泡 Pi 转运蛋白。最近的研究将 SPX 定义为一种 Pi 感应模块，它可以结合在高细胞 Pi 状态下产生的肌醇多磷酸信号分子 (InsPs)。我们在这里表明，Pi 缺乏条件或 SPX 结构域的突变严重损害了 VPT1 的转运活性。我们进一步鉴定了 VPT1 中的一个自动抑制结构域，该结构域抑制其转运活性。综合详细的结构功能分析结果，我们的研究表明，当 Pi 状态较低时，VPT1 处于自动抑制状态，而在高细胞 Pi 状态下，会产生 InsPs 并与 SPX 结构域结合，从而开启 VPT1 活性，将 Pi 输送到液泡中。这为 VPT1 介导的 Pi 感应和植物细胞中的稳态提供了一种自动调节机制。
