Chinchilla Delphine, Zipfel Cyril, Robatzek Silke, Kemmerling Birgit, Nürnberger Thorsten, Jones Jonathan D G, Felix Georg, Boller Thomas
Zurich-Basel Plant Science Center, Botanical Institute, University of Basel, Hebelstrasse 1, 4056 Basel, Switzerland.
Nature. 2007 Jul 26;448(7152):497-500. doi: 10.1038/nature05999. Epub 2007 Jul 11.
Plants sense potential microbial invaders by using pattern-recognition receptors to recognize pathogen-associated molecular patterns (PAMPs). In Arabidopsis thaliana, the leucine-rich repeat receptor kinases flagellin-sensitive 2 (FLS2) (ref. 2) and elongation factor Tu receptor (EFR) (ref. 3) act as pattern-recognition receptors for the bacterial PAMPs flagellin and elongation factor Tu (EF-Tu) (ref. 5) and contribute to resistance against bacterial pathogens. Little is known about the molecular mechanisms that link receptor activation to intracellular signal transduction. Here we show that BAK1 (BRI1-associated receptor kinase 1), a leucine-rich repeat receptor-like kinase that has been reported to regulate the brassinosteroid receptor BRI1 (refs 6,7), is involved in signalling by FLS2 and EFR. Plants carrying bak1 mutations show normal flagellin binding but abnormal early and late flagellin-triggered responses, indicating that BAK1 acts as a positive regulator in signalling. The bak1-mutant plants also show a reduction in early, but not late, EF-Tu-triggered responses. The decrease in responses to PAMPs is not due to reduced sensitivity to brassinosteroids. We provide evidence that FLS2 and BAK1 form a complex in vivo, in a specific ligand-dependent manner, within the first minutes of stimulation with flagellin. Thus, BAK1 is not only associated with developmental regulation through the plant hormone receptor BRI1 (refs 6,7), but also has a functional role in PRR-dependent signalling, which initiates innate immunity.
植物通过使用模式识别受体来识别病原体相关分子模式（PAMPs），从而感知潜在的微生物入侵者。在拟南芥中，富含亮氨酸重复序列的受体激酶鞭毛蛋白敏感2（FLS2）（参考文献2）和延伸因子Tu受体（EFR）（参考文献3）作为细菌PAMPs鞭毛蛋白和延伸因子Tu（EF-Tu）（参考文献5）的模式识别受体，并有助于抵抗细菌病原体。关于将受体激活与细胞内信号转导联系起来的分子机制，我们了解得还很少。在这里，我们表明BAK1（BRI1相关受体激酶1），一种富含亮氨酸重复序列的类受体激酶，据报道可调节油菜素内酯受体BRI1（参考文献6,7），参与了FLS2和EFR的信号传导。携带bak1突变的植物表现出正常的鞭毛蛋白结合，但鞭毛蛋白触发的早期和晚期反应异常，这表明BAK1在信号传导中起正向调节作用。bak1突变体植物在EF-Tu触发的早期反应中也表现出降低，但晚期反应没有降低。对PAMPs反应的降低不是由于对油菜素内酯的敏感性降低。我们提供的证据表明，在鞭毛蛋白刺激的最初几分钟内，FLS2和BAK1以特定的配体依赖方式在体内形成复合物。因此，BAK1不仅通过植物激素受体BRI1（参考文献6,7）参与发育调控，而且在启动先天免疫的PRR依赖信号传导中具有功能作用。
