Department of Plant Systems Biology, VIB, Ghent, Belgium.
Nat Chem Biol. 2012 May 6;8(6):583-9. doi: 10.1038/nchembio.958.
Receptor-mediated endocytosis is an integral part of signal transduction as it mediates signal attenuation and provides spatial and temporal dimensions to signaling events. One of the best-studied leucine-rich repeat receptor-like kinases in plants, BRASSINOSTEROID INSENSITIVE 1 (BRI1), perceives its ligand, the brassinosteroid (BR) hormone, at the cell surface and is constitutively endocytosed. However, the importance of endocytosis for BR signaling remains unclear. Here we developed a bioactive, fluorescent BR analog, Alexa Fluor 647-castasterone (AFCS), and visualized the endocytosis of BRI1-AFCS complexes in living Arabidopsis thaliana cells. Impairment of endocytosis dependent on clathrin and the guanine nucleotide exchange factor for ARF GTPases (ARF-GEF) GNOM enhanced BR signaling by retaining active BRI1-ligand complexes at the plasma membrane. Increasing the trans-Golgi network/early endosome pool of BRI1-BR complexes did not affect BR signaling. Our findings provide what is to our knowledge the first visualization of receptor-ligand complexes in plants and reveal clathrin- and ARF-GEF-dependent endocytic regulation of BR signaling from the plasma membrane.
受体介导的内吞作用是信号转导的一个组成部分，因为它介导信号衰减，并为信号事件提供空间和时间维度。在植物中，BRASSINOSTEROID INSENSITIVE 1（BRI1）是研究最多的富含亮氨酸重复受体样激酶之一，它在细胞表面感知其配体——油菜素甾体（BR）激素，并持续内吞。然而，内吞作用对 BR 信号转导的重要性仍不清楚。在这里，我们开发了一种生物活性的荧光 BR 类似物，Alexa Fluor 647-castasterone（AFCS），并在活体拟南芥细胞中可视化了 BRI1-AFCS 复合物的内吞作用。网格蛋白和 ARF GTP 酶（ARF-GEF）GNOM 依赖的内吞作用的损伤通过将活性 BRI1-配体复合物保留在质膜上增强了 BR 信号转导。增加 BRI1-BR 复合物的反式高尔基体网络/早期内体池不会影响 BR 信号转导。我们的发现提供了据我们所知植物中受体-配体复合物的首次可视化，并揭示了质膜中 BR 信号转导的网格蛋白和 ARF-GEF 依赖性内吞调节。
