SALT OVERLY SENSITIVE 1 is inhibited by clade D Protein phosphatase 2C D6 and D7 in Arabidopsis thaliana

背景回顾：The Salt Overly Sensitive (SOS) pathway is essential for maintaining sodium ion homeostasis in plants. This conserved pathway is activated by a calcium signaling-dependent phosphorylation cascade. 

提出问题：However, the identity of the phosphatases and their regulatory mechanisms that would deactivate the SOS pathway remain unclear. 

结果2-PP2C D6/D7：In this study, we demonstrate that PP2C.D6 and PP2C.D7, which belong to clade D of the protein phosphatase 2C (PP2C) subfamily in Arabidopsis thaliana, directly interact with SOS1 and inhibit its Na+/H+ antiporter activity under non-salt-stress conditions. 

结果2-ScaBP8：Upon salt stress, SOS3-LIKE CALCIUM BINDING PROTEIN8 (SCaBP8), a member of the SOS pathway, interacts with the PP2Cs and suppresses their phosphatase activity; simultaneously, SCaBP8 regulates the subcellular localization of PP2C.D6 by releasing it from the plasma membrane. 

结论1：Thus, we identified two negative regulators of the SOS pathway that repress SOS1 activity under non-stress conditions. These processes set the stage for the activation of SOS1 by the kinase SOS2 to achieve plant salt tolerance. 

结论2：Our results suggest that reversible phosphorylation/dephosphorylation is crucial for the regulation of the SOS pathway, and that calcium sensors play dual roles in activating/deactivating SOS2 and PP2C phosphatases under salt stress.

 摘 要 

盐过敏SOS途径对于维持植物钠离子稳态至关重要。该保守途径受到钙离子信号转导依赖性磷酸化级联所激活。但是，作用于SOS途径去磷酸化的磷酸酶及其调控机制还不清楚。本文中，作者发现在非盐胁迫条件下，拟南芥蛋白磷酸酶PP2C家族的D分枝蛋白PP2C.D6和PP2C.D7能够直接与SOS1互作，并抑制SOS1的钠离子/氢离子逆向转运活性。在盐胁迫下，SOS途径中的SOS3类似钙结合蛋白SCaBP8能够与PP2Cs互作，抑制PP2Cs蛋白的磷酸酶活性；同时，SCaBP8通过将PP2C.D6从质膜上释放来调控PP2C.D6的亚细胞定位。因此，作者鉴定到了SOS途径的两个负调控因子，可在非盐胁迫条件下抑制SOS1的活性。这些过程为激酶SOS2激活SOS1以实现植物耐盐性创造了条件。本文的研究结果揭示了磷酸化/去磷酸化的可逆性对于SOS途径的调控至关重要，且钙离子感受器在盐胁迫下激活/失活SOS2和PP2C磷酸酶中发挥双重作用。

** 郭 岩 **