Department of Biochemistry, University of Missouri, Columbia, Missouri 65211.
Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211.
Plant Physiol. 2017 Dec;175(4):1839-1852. doi: 10.1104/pp.17.01152. Epub 2017 Oct 25.
Plants perceive potential pathogens via the recognition of pathogen-associated molecular patterns (PAMPs) by surface-localized pattern recognition receptors, which initiates a series of intracellular responses that ultimately limit bacterial growth. PAMP responses include changes in intracellular protein phosphorylation, including the activation of mitogen-activated protein kinase (MAPK) cascades. MAP kinase phosphatases (MKPs), such as Arabidopsis () MKP1, are important negative regulators of MAPKs and play a crucial role in controlling the intensity and duration of MAPK activation during innate immune signaling. As such, the mutant lacking MKP1 displays enhanced PAMP responses and resistance against the virulent bacterium pv DC3000. Previous in vitro studies showed that MKP1 can be phosphorylated and activated by MPK6, suggesting that phosphorylation may be an important mechanism for regulating MKP1. We found that MKP1 was phosphorylated during PAMP elicitation and that phosphorylation stabilized the protein, resulting in protein accumulation after elicitation. MKP1 also can be stabilized by the proteasome inhibitor MG132, suggesting that MKP1 is constitutively degraded through the proteasome in the resting state. In addition, we investigated the role of MKP1 posttranslational regulation in plant defense by testing whether phenotypes of the Arabidopsis mutant could be complemented by expressing phosphorylation site mutations of MKP1. The phosphorylation of MKP1 was found to be required for some, but not all, of MKP1's functions in PAMP responses and defense against bacteria. Together, our results provide insight into the roles of phosphorylation in the regulation of MKP1 during PAMP signaling and resistance to bacteria.
植物通过位于表面的模式识别受体识别病原体相关分子模式（PAMPs）来感知潜在的病原体，这引发了一系列细胞内反应，最终限制了细菌的生长。PAMP 反应包括细胞内蛋白质磷酸化的变化，包括丝裂原活化蛋白激酶（MAPK）级联的激活。MAP 激酶磷酸酶（MKP），如拟南芥（Arabidopsis）MKP1，是 MAPKs 的重要负调控因子，在控制先天免疫信号转导过程中 MAPK 的激活强度和持续时间方面发挥着关键作用。因此，缺乏 MKP1 的 突变体表现出增强的 PAMP 反应和对毒性细菌 pv DC3000 的抗性。先前的体外研究表明，MKP1 可以被 MPK6 磷酸化和激活，这表明磷酸化可能是调节 MKP1 的重要机制。我们发现，在 PAMP 诱导时，MKP1 发生磷酸化，磷酸化稳定了该蛋白，导致诱导后蛋白积累。MKP1 还可以被蛋白酶体抑制剂 MG132 稳定，这表明在静息状态下，MKP1 通过蛋白酶体被持续降解。此外，我们通过测试 MKP1 的磷酸化位点突变是否可以互补 突变体的表型，研究了 MKP1 翻译后调控在植物防御中的作用。结果发现，MKP1 的磷酸化对于 MKP1 在 PAMP 反应和抵抗细菌中的一些功能是必需的，但不是所有功能都是必需的。总之，我们的研究结果提供了关于磷酸化在 PAMP 信号转导和细菌抗性过程中调节 MKP1 的作用的深入了解。
