2009年5月15日，北京生命科学研究所郭岩实验室在The Plant Cell杂志在线发表题为“Phosphorylation of SOS3-LIKE CALCIUM BINDING PROTEIN8 by SOS2 Protein Kinase Stabilizes Their Protein Complex and Regulates Salt Tolerance in Arabidopsis”的文章，该文章报道了SCaBP8在体内被SOS2磷酸化在调节植物耐盐性中的作用。

调节细胞中的离子平衡对植物的生长发育是至关重要的。研究表明SOS信号途径在调节植物钠钾平衡和耐盐性中起关键作用。钙结合蛋白SOS3和SCaBP8通过激活蛋白激酶SOS2保护拟南芥免受外界的盐胁迫。SOS3主要作用在根部，而SCaBP8主要作用在地上部分。由于它们异位表达后并不能相互恢复各自的表型，于是推测它们有着独特的调节机制。在这个研究中我们发现SOS2不能磷酸化SOS3，但却能够磷酸化SCaBP8。该磷酸化反应发生在膜上，并受盐诱导。它稳定了SCaBP8-SOS2的相互作用，并增强质膜钠氢转运蛋白的活性。当SCaBP8蛋白丝氨酸-237突变成丙氨酸时，SOS2不再能磷酸化SCaBP8。这个突变的蛋白也就不能够完全恢复scabp8盐敏感表型。而丝氨酸-237突变成能够模拟磷酸化的天冬氨酸则能够完全恢复scabp8的表型。这些结果表明SCaBP8被SOS2磷酸化是SOS信号途径调节拟南芥耐盐机制的重要一环。

该文章的第一作者为林慧馨，通讯作者为郭岩博士，该项研究由科技部863项目和北京市科委资助。

推荐原始出处：

Plant Cell May 15, 2009; 10.1105/tpc.109.066217

Phosphorylation of SOS3-LIKE CALCIUM BINDING PROTEIN8 by SOS2 Protein Kinase Stabilizes Their Protein Complex and Regulates Salt Tolerance in Arabidopsis

Huixin Lin 1, Yongqing Yang 1, Ruidang Quan 1, Imelda Mendoza 2, Yisheng Wu 1, Wenming Du 1, Shuangshuang Zhao 1, Karen S. Schumaker 3, José M. Pardo 2, and Yan Guo 1*

1 National Institute of Biological Sciences, Beijing, Zhongguancun Life Science Park, Beijing 102206, P.R. China
2 Instituto de Recursos Naturales y Agrobiología, Consejo Superior de Investigaciones Científicas, Sevilla 41012, Spain
3 Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721

The Salt Overly Sensitive (SOS) pathway plays an important role in the regulation of Na+/K+ ion homeostasis and salt tolerance in Arabidopsis thaliana. Previously, we reported that the calcium binding proteins SOS3 and SOS3-LIKE CALCIUM BINDING PROTEIN8 (SCaBP8) nonredundantly activate the protein kinase SOS2. Here, we show that SOS2 phosphorylates SCaBP8 at its C terminus but does not phosphorylate SOS3. In vitro, SOS2 phosphorylation of SCaBP8 was enhanced by the bimolecular interaction of SOS2 and SCaBP8 and did not require calcium ions. In vivo, this phosphorylation was induced by salt stress, occurred at the membrane, stabilized the SCaBP8-SOS2 interaction, and enhanced plasma membrane Na+/H+ exchange activity. When a Ser at position 237 in the SCaBP8 protein (the SOS2 phosphorylation target) was mutated to Ala, SCaBP8 was no longer phosphorylated by SOS2 and the mutant protein could not fully rescue the salt-sensitive phenotype of the scabp8 mutant. By contrast, when Ser-237 was mutated to Asp to mimic the charge of a phosphorylated Ser residue, the mutant protein rescued the scabp8 salt sensitivity. These data demonstrate that calcium sensor phosphorylation is a critical component of SOS pathway regulation of salt tolerance in Arabidopsis.