F-box protein, one of the building blocks of the SCF complex, functions in substrate recognition of the SCF subtype of E3 ubiquitin ligase. However, the role of F-box protein in salt stress is largely elusive in plants. Here, we report the characterization of an Arabidopsis salt-tolerant mutant est1 with significantly reduced sodium content and higher Na+/H+ antiporter activity after NaCl treatment compared to the wild-type. Over-expression of EST1 resulted in increased sensitivity to salt stress, suggesting that EST1 may act as a negative regulator for salt tolerance in Arabidopsis. EST1 encodes an F-box protein, which interacts with ASK4, ASK14, and ASK18, and is likely targeted to the endoplasmic reticulum. In addition, EST1 interacts with MKK4 and negatively regulates MKK4 protein levels and the activity of the plasma membrane Na+/H+ antiporter. Our findings demonstrate the existence of an EST1-MKK4 module that mediates salt sensitivity by regulating the activity of the plasma membrane Na+/H+ antiporter. These results provide important information for engineering salt-tolerant crops.

中文翻译：

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F-box 蛋白 EST1 通过调节质膜 Na+/H+ 逆向转运活性调节拟南芥的耐盐性

F-box 蛋白是 SCF 复合体的组成部分之一，在 E3 泛素连接酶 SCF 亚型的底物识别中起作用。然而，F-box 蛋白在盐胁迫中的作用在植物中很大程度上是难以捉摸的。在这里，我们报告了拟南芥耐盐突变体 est1 的特征，与野生型相比，NaCl 处理后钠含量显着降低，Na+/H+ 逆向转运蛋白活性更高。EST1 的过度表达导致对盐胁迫的敏感性增加，表明 EST1 可能作为拟南芥耐盐性的负调节因子。EST1 编码一种 F-box 蛋白，它与 ASK4、ASK14 和 ASK18 相互作用，并且可能靶向内质网。此外，EST1 与 MKK4 相互作用并负调节 MKK4 蛋白水平和质膜 Na+/H+ 逆向转运蛋白的活性。我们的研究结果证明了 EST1-MKK4 模块的存在，该模块通过调节质膜 Na+/H+ 逆向转运蛋白的活性来介导盐敏感性。这些结果为工程耐盐作物提供了重要信息。