Phosphoinositides function as lipid signals in plant development and stress tolerance by binding with partner proteins. We previously reported that Arabidopsis (Arabidopsis thaliana) phosphoinositide-specific phospholipase C2 functions in the endoplasmic reticulum (ER) stress response. However, the underlying molecular mechanisms of how phosphoinositides act in the ER stress response remain elusive. Here, we report that a phosphoinositide-binding protein, SMALLER TRICHOMES WITH VARIABLE BRANCHES (SVB), is involved in the ER stress tolerance. SVB contains a DUF538 domain with unknown function; orthologs are exclusively found in Viridiplantae. We established that SVB is ubiquitously expressed in plant tissues and is localized to the ER, Golgi apparatus, prevacuolar compartment, and plasma membrane. The knockout mutants of svb showed enhanced tolerance to ER stress, which was genetically complemented by transducing genomic SVB SVB showed time-dependent induction after tunicamycin-induced ER stress, which depended on IRE1 and bZIP60 but not bZIP17 and bZIP28 in the unfolded protein response (UPR). A protein-lipid overlay assay showed specific binding of SVB to phosphatidylinositol 3,5-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate. SVB is therefore suggested to be the plant-specific phosphoinositide-binding protein whose expression is controlled by the UPR through the IRE1-bZIP60 pathway in Arabidopsis.

中文翻译：

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展开的蛋白质反应通过IRE1-bZIP60途径调节磷酸肌醇结合蛋白。

磷酸肌醇通过与伴侣蛋白结合，在植物发育和胁迫耐受性中起脂质信号的作用。我们以前曾报道过，拟南芥（Arabidopsis thaliana）磷酸肌醇特异性磷脂酶C2在内质网（ER）应激反应中起作用。然而，磷酸肌醇如何在内质网应激反应中的潜在分子机制仍然难以捉摸。在这里，我们报告说，磷酸肌醇结合蛋白，具有可变支链的更小毛囊（SVB），参与了内质网应激耐受性。SVB包含功能未知的DUF538域；直系同源物仅在Vi科植物中发现。我们确定，SVB在植物组织中普遍表达，并且位于ER，高尔基体，前真空室和质膜上。svb的敲除突变体显示出对ER胁迫的耐受性增强，这是通过转导基因组SVB遗传互补的.SVB在衣霉素诱导的ER胁迫后表现出时间依赖性诱导，这取决于IRE1和bZIP60，但在未折叠的蛋白应答中不依赖bZIP17和bZIP28 UPR）。蛋白质-脂质重叠测定显示SVB与磷脂酰肌醇3,5-双磷酸酯和磷脂酰肌醇3,4,5-三磷酸酯特异性结合。因此，SVB被认为是植物特异性的磷酸肌醇结合蛋白，其表达受拟南芥中通过IRE1-bZIP60途径的UPR控制。其在展开的蛋白应答（UPR）中取决于IRE1和bZIP60，但不取决于bZIP17和bZIP28。蛋白质-脂质重叠测定显示SVB与磷脂酰肌醇3,5-双磷酸酯和磷脂酰肌醇3,4,5-三磷酸酯特异性结合。因此，SVB被认为是植物特异性的磷酸肌醇结合蛋白，其表达受拟南芥中通过IRE1-bZIP60途径的UPR控制。其在展开的蛋白应答（UPR）中取决于IRE1和bZIP60，但不取决于bZIP17和bZIP28。蛋白质-脂质重叠测定显示SVB与磷脂酰肌醇3,5-双磷酸酯和磷脂酰肌醇3,4,5-三磷酸酯特异性结合。因此，SVB被认为是植物特异性的磷酸肌醇结合蛋白，其表达受拟南芥中通过IRE1-bZIP60途径的UPR的控制。