Department for Biochemistry of Plant Interactions, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120 Halle, Germany.
Essays Biochem. 2022 Sep 30;66(5):621-634. doi: 10.1042/EBC20210088.
Plant immunity is crucial to plant health but comes at an expense. For optimal plant growth, tight immune regulation is required to prevent unnecessary rechannelling of valuable resources. Pattern- and effector-triggered immunity (PTI/ETI) represent the two tiers of immunity initiated after sensing microbial patterns at the cell surface or pathogen effectors secreted into plant cells, respectively. Recent evidence of PTI-ETI cross-potentiation suggests a close interplay of signalling pathways and defense responses downstream of perception that is still poorly understood. This review will focus on controls on plant immunity through phosphorylation, a universal and key cellular regulatory mechanism. Rather than a complete overview, we highlight "what's new in protein kinase/phosphatase signalling" in the immunity field. In addition to phosphoregulation of components in the pattern recognition receptor (PRR) complex, we will cover the actions of the major immunity-relevant intracellular protein kinases/phosphatases in the 'signal relay', namely calcium-regulated kinases (e.g. calcium-dependent protein kinases, CDPKs), mitogen-activated protein kinases (MAPKs), and various protein phosphatases. We discuss how these factors define a phosphocode that generates cellular decision-making 'logic gates', which contribute to signalling fidelity, amplitude, and duration. To underscore the importance of phosphorylation, we summarize strategies employed by pathogens to subvert plant immune phosphopathways. In view of recent game-changing discoveries of ETI-derived resistosomes organizing into calcium-permeable pores, we speculate on a possible calcium-regulated phosphocode as the mechanistic control of the PTI-ETI continuum.
植物免疫对于植物的健康至关重要，但这是有代价的。为了实现植物的最佳生长，需要严格的免疫调控，以防止宝贵资源的不必要再分配。模式触发免疫（PTI）和效应子触发免疫（ETI）分别代表了在细胞表面感知微生物模式或病原体效应子分泌到植物细胞后启动的两个免疫层次。最近的 PTI-ETI 交叉增强的证据表明，感知下游的信号通路和防御反应之间存在密切的相互作用，但这仍然知之甚少。本综述将重点关注通过磷酸化控制植物免疫，磷酸化是一种普遍而关键的细胞调节机制。我们不是全面概述，而是强调免疫领域“蛋白激酶/磷酸酶信号中的新进展”。除了模式识别受体（PRR）复合物中成分的磷酸化调控外，我们还将涵盖主要与免疫相关的细胞内蛋白激酶/磷酸酶在“信号传递”中的作用，即钙调节激酶（如钙依赖性蛋白激酶，CDPKs）、丝裂原激活蛋白激酶（MAPKs）和各种蛋白磷酸酶。我们讨论了这些因素如何定义产生细胞决策“逻辑门”的磷酸化代码，这有助于信号保真度、幅度和持续时间。为了强调磷酸化的重要性，我们总结了病原体用来颠覆植物免疫磷酸途径的策略。鉴于最近关于 ETI 衍生的抗性小体形成钙渗透性孔的改变游戏规则的发现，我们推测钙调节磷酸化代码可能是 PTI-ETI 连续体的机制控制。
