State Key Laboratory of Ecological Control of Fujian-Taiwan Crop Pests, Key Laboratory of Ministry of Education for Genetics, Breeding and Multiple Utilization of Crops, Plant Immunity Center, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
Ministerial and Provincial Joint Innovation Centre for Safety Production of Cross-Strait Crops, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
Plant Physiol. 2023 Dec 30;194(1):578-591. doi: 10.1093/plphys/kiad472.
Mitogen-activated protein kinase (MAPK/MPK) cascades are key signaling modules that regulate plant immunity. ENHANCED DISEASE RESISTANCE1 (EDR1) encodes a Raf-like MAPK kinase kinase (MAPKKK) that negatively regulates plant defense in Arabidopsis (Arabidopsis thaliana). The enhanced resistance of edr1 requires MAPK KINASE4 (MKK4), MKK5, and MPK3. Although the edr1 mutant displays higher MPK3/6 activation, the mechanism by which plants increase MAPK cascade activation remains elusive. Our previous study showed that MAPKKK5 is phosphorylated at the Ser-90 residue in edr1 mutants. In this study, we demonstrated that the enhanced disease resistance of edr1 required MAPKKK5. Phospho-dead MAPKKK5S90A partially impaired the resistance of edr1, and the expression of phospho-mimetic MAPKKK5S90D in mapkkk5-2 resulted in enhanced resistance to the powdery mildew Golovinomyces cichoracearum strain UCSC1 and the bacterial pathogen Pseudomonas syringae pv. tomato (Pto) strain DC3000. Thus, Ser-90 phosphorylation in MAPKKK5 appears to play a crucial role in disease resistance. However, MAPKKK5-triggered cell death was not suppressed by EDR1. Furthermore, activated MPK3 phosphorylated the N terminus of MAPKKK5, and Ser-90 was one of the phosphorylated sites. Ser-90 phosphorylation increased MAPKKK5 stability, and EDR1 might negatively regulate MAPK cascade activation by suppressing the MPK3-mediated feedback regulation of MAPKKK5. Taken together, these results indicate that MPK3 phosphorylates MAPKKK5 to enhance MAPK cascade activation and disease resistance in edr1 mutants.
丝裂原活化蛋白激酶（MAPK/MPK）级联是调节植物免疫的关键信号模块。增强疾病抗性 1（EDR1）编码一种 Raf 样 MAPK 激酶激酶（MAPKKK），在拟南芥（Arabidopsis thaliana）中负调控植物防御。edr1 的增强抗性需要 MAPK 激酶 4（MKK4）、MKK5 和 MPK3。尽管 edr1 突变体显示出更高的 MPK3/6 激活，但植物增加 MAPK 级联激活的机制仍不清楚。我们之前的研究表明，EDR1 突变体中的 MAPKKK5 在丝氨酸-90 残基上被磷酸化。在这项研究中，我们证明了 EDR1 增强的抗病性需要 MAPKKK5。磷酸化失活的 MAPKKK5S90A 部分损害了 edr1 的抗性，而在 mapkkk5-2 中表达磷酸化模拟的 MAPKKK5S90D 导致对白粉病病原菌 Golovinomyces cichoracearum 菌株 UCSC1 和细菌性病原菌 Pseudomonas syringae pv. tomato（Pto）菌株 DC3000 的抗性增强。因此，MAPKKK5 中的丝氨酸-90 磷酸化似乎在抗病性中起着至关重要的作用。然而，EDR1 并没有抑制 MAPKKK5 触发的细胞死亡。此外，激活的 MPK3 磷酸化 MAPKKK5 的 N 端，丝氨酸-90 是磷酸化位点之一。丝氨酸-90 磷酸化增加了 MAPKKK5 的稳定性，EDR1 可能通过抑制 MPK3 介导的 MAPKKK5 的反馈调节来负调控 MAPK 级联的激活。总之，这些结果表明，MPK3 磷酸化 MAPKKK5 以增强 edr1 突变体中的 MAPK 级联激活和抗病性。
