类受体激酶（RLKs）在完成信号转导后需要迅速灭活以维持细胞内稳态的平衡，26S蛋白酶体介导的蛋白质降解是RLKs灭活的重要途径。多泛素化是蛋白质降解的前提，然而介导RLKs多泛素化修饰的E3s却鲜有报道。SIT1的激酶活性受盐胁迫迅速激活，但灭活机制不清楚。我们发现，SIT1与E3泛素连接酶PUBs家族的E3A有直接的相互作用，且这种相互作用依赖SIT1的激酶活性，表明E3A倾向于结合并降解有活性的SIT1。另外，一些SNP引起的蛋白序列变化降低了SIT1的磷酸化水平，削弱了SIT1与E3A的相互作用，延缓了SIT1的蛋白降解，表明SIT1的活性受这些SNP的调节。接下来的研究工作：1）E3A泛素化降解SIT1的分子机制；2）SNP引起的SIT1的活性变化是否影响、如何影响SIT1的敏盐功能。这些研究有助于深入解析SIT1的敏盐机理，也有助于进一步拓展植物抗盐机理的研究并用于农作物改良。

Receptor-like kinases (RLKs) are important components of cell signal transduction, and need to be rapidly inactivated after signal transduction to maintain the balance of intracellular homeostasis. The degradation of targeted substrates mediated by 26S proteasome is an important pathway for the inactivation of RLKs. Polyubiquitination is a prerequisite for protein degradation, and the substrate specificity of polyubiquitination is usually determined by E3 ubiquitin ligases. Until now, only a very few E3s have been reported to mediate the polyubiquitination of RLKs. The kinase activity of SIT1 is rapidly activated by salt stress, but the inactivation mechanism of SIT1 is still obscure. In this study, we found that SIT1 interacts directly with E3A, an E3 ubiquitin ligase of the PUBs family, and the interaction largely depends on the kinase activity of SIT1, indicating that E3A tends to bind and degrade SIT1 with bioactivity. In addition, we found that the protein sequence of SIT1 was changed by some SNPs in the salt-tolerant cultivars. And the protein sequence differences of SIT1 caused by these SNPs reduced the phosphorylation level of SIT1, weakened the interaction between SIT1 and E3A, and also delayed the degradation rate of SIT1, suggesting that the bioactivity of SIT1 is regulated by these SNPs. Therefore, the lower bioactivity of SIT1 probably be related to the salt-tolerant phenotype in the salt-tolerant cultivars. In future, we will delve into the molecular mechanism of SIT1 ubiquitination and degradation, and try to explore whether and how the differences of SIT1 bioactivity caused by these SNPs affects SIT1-mediated salt sensitivity. These works are of great significance for further understanding the salt-sensitive mechanism of SIT1, and for further expanding the research of salt-resistant mechanism of plants and for crop improvement.