In plant cells, environmental stressors promote changes in connectivity between the cortical endoplasmic reticulum (ER) and the plasma membrane (PM). Although this process is tightly regulated in space and time, the molecular signals and structural components mediating these changes in interorganelle communication are only starting to be characterized. In this report, we confirm the presence of a putative tethering complex containing the synaptotagmins 1 and 5 (SYT1 and SYT5) and the Ca²⁺- and lipid-binding protein 1 (CLB1/SYT7). This complex is enriched at ER–PM contact sites (EPCSs), has slow responses to changes in extracellular Ca²⁺, and displays severe cytoskeleton-dependent rearrangements in response to the trivalent lanthanum (La³⁺) and gadolinium (Gd³⁺) rare earth elements (REEs). Although REEs are generally used as non-selective cation channel blockers at the PM, here we show that the slow internalization of REEs into the cytosol underlies the activation of the Ca²⁺/calmodulin intracellular signaling, the accumulation of phosphatidylinositol-4-phosphate (PI4P) at the PM, and the cytoskeleton-dependent rearrangement of the SYT1/SYT5 EPCS complexes. We propose that the observed EPCS rearrangements act as a slow adaptive response to sustained stress conditions, and that this process involves the accumulation of stress-specific phosphoinositide species at the PM.

中文翻译：

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稀土元素诱导拟南芥中 SYT1/SYT5 内质网-质膜接触位点复合物的细胞骨架依赖性和 PI4P 相关重排。

在植物细胞中，环境压力源促进皮质内质网 (ER) 和质膜 (PM) 之间连接性的变化。尽管这一过程在空间和时间上受到严格调控，但介导这些细胞间通讯变化的分子信号和结构成分才刚刚开始被表征。在本报告中，我们确认了一种假定的束缚复合物的存在，该复合物包含突触结合蛋白 1 和 5（SYT1 和 SYT5）以及 Ca ²⁺ - 和脂质结合蛋白 1（CLB1/SYT7）。^{这种复合物在 ER-PM 接触位点 (EPCS) 富集，对细胞外 Ca 2+}的变化反应缓慢，并且对三价镧 (La ³⁺ ) 和钆 (Gd)的反应表现出严重的细胞骨架依赖性重排³⁺ ) 稀土元素 (REE)。尽管 REEs 通常在 PM 中用作非选择性阳离子通道阻滞剂，但我们在此表明​​ REEs 缓慢内化到细胞质中是 Ca ²⁺ /钙调蛋白细胞内信号的激活、4-磷酸磷脂酰肌醇的积累的基础。 PI4P）在 PM，以及 SYT1/SYT5 EPCS 复合物的细胞骨架依赖性重排。我们建议观察到的 EPCS 重排作为对持续应激条件的缓慢适应性反应，并且该过程涉及 PM 中应激特异性磷酸肌醇物质的积累。