Membrane lipids, and especially phosphoinositides, are differentially enriched within the eukaryotic endomembrane system. This generates a landmark code by modulating the properties of each membrane. Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] specifically accumulates at the plasma membrane in yeast, animal and plant cells, where it regulates a wide range of cellular processes including endocytic trafficking. However, the functional consequences of mispatterning PI(4,5)P₂ in plants are unknown. Here, we functionally characterized the putative phosphoinositide phosphatase SUPPRESSOR OF ACTIN9 (SAC9) in Arabidopsis thaliana (Arabidopsis). We found that SAC9 depletion led to the ectopic localization of PI(4,5)P₂ on cortical intracellular compartments, which depends on PI4P and PI(4,5)P₂ production at the plasma membrane. SAC9 localizes to a subpopulation of trans-Golgi Network/early endosomes that are enriched in a region close to the cell cortex and that are coated with clathrin. Furthermore, it interacts and colocalizes with Src Homology 3 Domain Protein 2 (SH3P2), a protein involved in endocytic trafficking. In the absence of SAC9, SH3P2 localization is altered and the clathrin-mediated endocytosis rate is reduced. Together, our results highlight the importance of restricting PI(4,5)P₂ at the plasma membrane and illustrate that one of the consequence of PI(4,5)P₂ misspatterning in plants is to impact the endocytic trafficking.

中文翻译：

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拟南芥 SAC9 酶在早期内体的皮质群中富集，并在质膜上限制 PI(4,5)P2

膜脂，尤其是磷酸肌醇，在真核细胞内膜系统中的富集程度不同。这通过调节每个膜的特性来生成一个地标代码。磷脂酰肌醇 4,5-二磷酸 [PI(4,5)P ₂ ] 特异性地在酵母、动物和植物细胞的质膜上积累，在那里它调节广泛的细胞过程，包括内吞运输。然而，错误模式 PI(4,5)P ₂在植物中的功能后果尚不清楚。在这里，我们在功能上表征了拟南芥中推定的肌动蛋白 9 ( SAC9 )磷酸肌醇磷酸酶抑制因子（拟南芥）。我们发现 SAC9 耗竭导致 PI(4,5)P ₂在皮质细胞内隔间的异位定位，这取决于质膜上 PI4P 和 PI(4,5)P ₂的产生。SAC9 定位于反高尔基网络/早期内体的亚群，这些亚群在靠近细胞皮层的区域富集，并涂有网格蛋白。此外，它与 Src Homology 3 Domain Protein 2 (SH3P2) 相互作用并共定位，这是一种参与内吞运输的蛋白质。在没有 SAC9 的情况下，SH3P2 定位发生改变，网格蛋白介导的内吞率降低。总之，我们的结果突出了限制 PI(4,5)P _{2的重要性}在质膜上，并说明植物中 PI(4,5)P ₂错误模式的后果之一是影响内吞运输。