病程相关基因非表达子1（NPR1）：植物抗病信号网络中的关键节点

最早从拟南芥（Arabidopsis thaliana）中克隆到的NPR1（nonexpressor of pathogenesis-related genes 1）基因是调控植物病害抗性的一个关键基因。它不仅对植物系统获得抗性（systemic acquired resistance,SAR）和诱导系统抗性（induced systemic resistance, ISR）起核心调控作用,而且是植物基础抗性（basic resistance）以及由抗病基因（resistance gene,R）决定的抗性的重要调控因子。氧化突发（oxidative burst）造成的强还原势导致NPR1蛋白还原成单体,以及NPR1单体在细胞核内的积累是诱导水杨酸（salicylic acid,SA）介导的PR（pathogenesis-related）基因表达和SAR产生的充分必要条件。NPR1通过与TGA转录因子的相互作用调控PR基因表达。NPR1作为多种信号途径的交叉点,与某些WRKY转录因子和NPR4一起,在调节和平衡SA和茉莉酸信号传导途径中起关键作用。NPR1的这种调控作用在细胞质内进行,通过遗传工程将其用于植物保护有很好的应用前景。     

Redox Regulation of the NPR1-TGA1 System of Arabidopsis thaliana by Nitric Oxide

The role of reactive oxygen and nitrogen species in local and systemic defense reactions is well documented. NPR1 and TGA1 are key redox-controlled regulators of systemic acquired resistance in plants. NPR1 monomers interact with the reduced form of TGA1, which targets the activation sequence-1 (as-1) element of the promoter region of defense proteins. Here, we report the effect of the physiological nitric oxide donor S-nitrosoglutathione on the NPR1/TGA1 regulation system in Arabidopsis thaliana. Using the biotin switch method, we demonstrate that both NPR1 and TGA1 are S-nitrosylated after treatment with S-nitrosoglutathione. Mass spectrometry analyses revealed that the Cys residues 260 and 266 of TGA1 are S-nitrosylated and S-glutathionylated even at GSNO concentrations in the low micromolar range. Furthermore, we showed that S-nitrosoglutathione protects TGA1 from oxygen-mediated modifications and enhances the DNA binding activity of TGA1 to the as-1 element in the presence of NPR1. In addition, we observed that the translocation of NPR1 into the nucleus is promoted by nitric oxide. Taken together, our results suggest that nitric oxide is a redox regulator of the NPR1/TGA1 system and that they underline the importance of nitric oxide in the plant defense response.