Department of Biochemistry and Biophysics, and Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, Texas 77843.
Shanghai Key Laboratory of Plant Molecular Sciences, College of Life Sciences, Shanghai Normal University, Shanghai, 200234 China.
Plant Physiol. 2019 May;180(1):543-558. doi: 10.1104/pp.18.01503. Epub 2019 Feb 19.
Plants have evolved many receptor-like kinases (RLKs) to sense extrinsic and intrinsic cues. The signaling pathways mediated by multiple Leucine-rich repeat (LRR) RLK (LRR-RLK) receptors require ligand-induced receptor-coreceptor heterodimerization and transphosphorylation with BRI1-ASSOCIATED RECEPTOR KINASE1 (BAK1)/SOMATIC EMBRYOGENESIS RECEPTOR KINASES family LRR-RLKs. Here we reveal an additional layer of regulation of BAK1 via a Ca-dependent proteolytic cleavage process that is conserved in Arabidopsis (), , and The proteolytic cleavage of BAK1 is intrinsically regulated in response to developmental cues and immune stimulation. The surface-exposed Asp (D) residue of BAK1 is critical for its proteolytic cleavage and plays an essential role in BAK1-regulated plant immunity, growth hormone brassinosteroid-mediated responses, and cell death containment. BAK1 mutation impairs BAK1 phosphorylation on its substrate BOTRYTIS-INDUCED KINASE1 (BIK1), and its plasma membrane localization. Intriguingly, it aggravates BAK1 overexpression-triggered cell death independent of BIK1, suggesting that maintaining homeostasis of BAK1 through a proteolytic process is crucial to control plant growth and immunity. Our data reveal that in addition to layered transphosphorylation in the receptor complexes, the proteolytic cleavage is an important regulatory process for the proper functions of the shared coreceptor BAK1 in diverse cellular signaling pathways.
植物已经进化出许多受体样激酶（RLKs）来感知外在和内在的信号。由多个富含亮氨酸重复（LRR）RLK（LRR-RLK）受体介导的信号通路需要配体诱导的受体-共受体异二聚化以及与 BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE1（BAK1）/SOMATIC EMBRYOGENESIS RECEPTOR KINASES 家族 LRR-RLK 的转磷酸化。在这里，我们揭示了 BAK1 的另一个调控层，通过钙依赖的蛋白水解切割过程，该过程在拟南芥（）、（）和（）中保守。BAK1 的蛋白水解切割在本质上受到发育信号和免疫刺激的调节。BAK1 表面暴露的天冬氨酸（D）残基对于其蛋白水解切割至关重要，并且在 BAK1 调节的植物免疫、生长激素油菜素内酯介导的反应和细胞死亡控制中发挥重要作用。BAK1 突变会损害其底物 BOTRYTIS-INDUCED KINASE1（BIK1）上的 BAK1 磷酸化及其质膜定位。有趣的是，它加剧了 BAK1 过表达触发的细胞死亡，而不依赖于 BIK1，这表明通过蛋白水解过程维持 BAK1 的内稳态对于控制植物生长和免疫至关重要。我们的数据表明，除了受体复合物中的层叠转磷酸化之外，蛋白水解切割是共享共受体 BAK1 在多种细胞信号通路中发挥正常功能的重要调节过程。
