Chen Tzu-Yi, Gong Rui-Wen, Chen Bo-Wei, Lin Yi-Hsien
Department of Plant Medicine, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan.
Plants (Basel). 2025 Jul 3;14(13):2044. doi: 10.3390/plants14132044.
The immune response triggered when plant cell surface receptors recognize pathogen-associated molecular patterns (PAMPs) is known as PAMP-triggered immunity (PTI). Several studies have demonstrated that extracellular plant ferredoxin-like protein (PFLP) can enhance PTI signaling, thereby conferring resistance to bacterial diseases in various plants. The C-terminal casein kinase II (CK2) phosphorylation region of PFLP is essential for strengthening PTI. However, whether phosphorylation at this site directly enhances PTI signaling and consequently increases plant disease resistance remains unclear. To investigate this, site-directed mutagenesis was used to generate PFLPT90A, a non-phosphorylatable mutant, and PFLPT90D, a phospho-mimetic mutant, for functional analysis. Based on the experimental results, none of the recombinant proteins were able to enhance the hypersensitive response induced by the HrpN protein or increase resistance to the soft rot pathogen subsp. ECC17. These findings suggest that phosphorylation at the T90 residue might be essential for PFLP-mediated enhancement of plant immune responses, implying that this post-translational modification is likely required for its disease resistance function in planta. To further explore the relationship between PFLP phosphorylation and endogenous CK2, the insertion mutant and the complemented line were analyzed under treatment with flg22 from pv. . The effects of PFLP on the hypersensitive response, rapid oxidative burst, callose deposition, and susceptibility to soft rot confirmed that CK2 is required for these immune responses. Furthermore, expression analysis of PTI-related genes and in the mitogen-activated protein kinase (MAPK) signaling pathway demonstrated that CK2 is necessary for PFLP to enhance flg22-induced immune signaling. Taken together, these findings suggest that PFLP enhances resistance to bacterial soft rot primarily by promoting the MAPK signaling pathway triggered by PAMP recognition, with CK2-mediated phosphorylation being essential for its function.
当植物细胞表面受体识别病原体相关分子模式（PAMPs）时触发的免疫反应被称为PAMP触发的免疫（PTI）。多项研究表明，细胞外植物铁氧还蛋白样蛋白（PFLP）可增强PTI信号传导，从而赋予多种植物对细菌病害的抗性。PFLP的C末端酪蛋白激酶II（CK2）磷酸化区域对于增强PTI至关重要。然而，该位点的磷酸化是否直接增强PTI信号传导并因此增加植物抗病性仍不清楚。为了研究这一点，使用定点诱变产生了不可磷酸化的突变体PFLPT90A和模拟磷酸化的突变体PFLPT90D进行功能分析。基于实验结果，没有一种重组蛋白能够增强由HrpN蛋白诱导的过敏反应或增加对软腐病原菌亚种ECC17的抗性。这些发现表明，T90残基的磷酸化可能是PFLP介导的植物免疫反应增强所必需的，这意味着这种翻译后修饰可能是其在植物中抗病功能所必需的。为了进一步探索PFLP磷酸化与内源性CK2之间的关系，在来自pv.的flg22处理下分析了插入突变体和互补系。PFLP对过敏反应、快速氧化爆发、胼胝质沉积和对软腐病易感性的影响证实了CK2是这些免疫反应所必需的。此外，对丝裂原活化蛋白激酶（MAPK）信号通路中PTI相关基因和的表达分析表明，CK2是PFLP增强flg22诱导的免疫信号所必需的。综上所述，这些发现表明PFLP主要通过促进由PAMP识别触发的MAPK信号通路来增强对细菌性软腐病的抗性，CK2介导的磷酸化对其功能至关重要。
