Nucleocytoplasmic trafficking and turnover mechanisms of BRASSINAZOLE RESISTANT1 in Arabidopsis thaliana
Nucleocytoplasmic trafficking and turnover mechanisms of BRASSINAZOLE RESISTANT1 in Arabidopsis thaliana
复制标题
DOI：
10.1073/pnas.2101838118
复制
发表时间：
2021-08-17
影响因子：
11.1
通讯作者：
Tang, Wenqiang
中科院分区：
文献类型：
--
作者：
Wang, Ruiju;Wang, Ruixuan;Tang, Wenqiang
调节核质内信号成分的运输，尤其是转录因子，是响应细胞外刺激的信号转导的关键步骤。在油菜素类固醇(BR)信号转导途径中，BRASSINAZOLE RESISTANT1(BZR1)家族的转录因子在调节BR调控的基因表达中起着至关重要的作用。BZR1的亚细胞定位和转录活性受到可逆蛋白质磷酸化的严格调控；然而，其潜在的机制尚不清楚。在这里，我们提供了BZR1的磷酸化和去磷酸化都发生在细胞核中的证据，并且BR调节的BZR1的核定位不依赖于它与蛋白磷酸酶2A的相互作用或去磷酸化。利用可光转化的荧光蛋白KEELD作为活标记来区分新合成的BZR1和现有的BZR1，我们证明了BR处理将细胞质的BZR1招募到细胞核，这可以解释植物对BR的快速反应。此外，我们获得了两种调节植物细胞BZR1丰度的蛋白质周转机制的证据：一种是BR和26S蛋白体非依赖的结构性降解机制，另一种是BR激活的26S蛋白酶体依赖的蛋白降解机制。最后，即使在没有BR信号的情况下，用26S蛋白小体的抑制剂处理植物细胞也能诱导BZR1的核定位和去磷酸化。基于这些结果，我们提出了一个模型来解释BR信号如何调节BZR1的核质转运和可逆磷酸化。
Regulation of the nucleocytoplasmic trafficking of signaling components, especially transcription factors, is a key step of signal transduction in response to extracellular stimuli. In the brassinosteroid (BR) signal transduction pathway, transcription factors from the BRASSINAZOLE RESISTANT1 (BZR1) family are essential in mediating BR-regulated gene expression. The subcellular localization and transcriptional activity of BZR1 are tightly regulated by reversible protein phosphorylation; however, the underlying mechanism is not well understood. Here, we provide evidence that both BZR1 phosphorylation and dephosphorylation occur in the nucleus and that BR-regulated nuclear localization of BZR1 is independent from its interaction with, or dephosphorylation by, protein phosphatase 2A. Using a photoconvertible fluorescent protein, Kaede, as a living tag to distinguish newly synthesized BZR1 from existing BZR1, we demonstrated that BR treatment recruits cytosolic BZR1 to the nucleus, which could explain the fast responses of plants to BR. Additionally, we obtained evidence for two types of protein turnover mechanisms that regulate BZR1 abundance in plant cells: a BR- and 26S proteosome-independent constitutive degradation mechanism and a BR-activated 26S proteosome-dependent proteolytic mechanism. Finally, treating plant cells with inhibitors of 26S proteosome induces the nuclear localization and dephosphorylation of BZR1, even in the absence of BR signaling. Based on these results, we propose a model to explain how BR signaling regulates the nucleocytoplasmic trafficking and reversible phosphorylation of BZR1.