The plant macronutrient phosphorus is a scarce resource and plant-available phosphate is limiting in most soil types. Generally, a gene regulatory module called the phosphate starvation response (PSR) enables efficient phosphate acquisition by roots and translocation to other organs. Plants growing on moderate to nutrient-rich soils need to co-ordinate availability of different nutrients and repress the highly efficient PSR to adjust phosphate acquisition to the availability of other macro- and micronutrients, and in particular nitrogen. PSR repression is mediated by a small family of single SYG1/Pho81/XPR1 (SPX) domain proteins. The SPX domain binds higher order inositol pyrophosphates that signal cellular phosphorus status and modulate SPX protein interaction with PHOSPHATE STARVATION RESPONSE1 (PHR1), the central transcriptional regulator of PSR. Sequestration by SPX repressors restricts PHR1 access to PSR gene promoters. Here we focus on SPX4 that primarily acts in shoots and sequesters many transcription factors other than PHR1 in the cytosol to control processes beyond the classical PSR, such as nitrate, auxin, and jasmonic acid signalling. Unlike SPX1 and SPX2, SPX4 is subject to proteasomal degradation not only by singular E3 ligases, but also by SCF–CRL complexes. Emerging models for these different layers of control and their consequences for plant acclimation to the environment will be discussed.

中文翻译：

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SPX 蛋白、泛素化机制和信号分子之间的动态相互作用，用于全植物水平的应激适应

植物大量营养素磷是一种稀缺资源，并且植物可利用的磷酸盐在大多数土壤类型中都受到限制。一般来说，称为磷酸盐饥饿反应（PSR）的基因调节模块能够使根有效地获取磷酸盐并转运到其他器官。在中等到营养丰富的土壤上生长的植物需要协调不同养分的可用性，并抑制高效的 PSR，以根据其他常量和微量营养素（特别是氮）的可用性调整磷酸盐的获取。PSR 抑制由单个 SYG1/Pho81/XPR1 (SPX) 结构域蛋白小家族介导。SPX 结构域结合高阶肌醇焦磷酸，发出细胞磷状态信号并调节 SPX 蛋白与磷酸饥饿反应 1 (PHR1)（PSR 的中央转录调节因子）的相互作用。SPX 阻遏物的隔离限制了 PHR1 接触 PSR 基因启动子。在这里，我们重点关注 SPX4，它主要在芽中发挥作用，并隔离细胞质中除 PHR1 之外的许多转录因子，以控制经典 PSR 之外的过程，例如硝酸盐、生长素和茉莉酸信号传导。与 SPX1 和 SPX2 不同，SPX4 不仅会被单一 E3 连接酶降解，还会被 SCF-CRL 复合物降解。将讨论这些不同控制层的新兴模型及其对植物适应环境的影响。