Su Shiqi, Jiang Yimin, Zhu Xiang, Yu Shibo, Wang Fuxiang, Xue Li, Cui Haitao
Key Laboratory of Ministry of Education for Genetics, Breeding and Multiple Utilization of Crops, Fujian University Key Laboratory for Plant-Microbe Interaction, Plant Immunity Center, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
College of Life Science, Shandong Agricultural University, Tai'an, Shandong 271018, China.
Plant Physiol. 2024 Dec 2;196(4):3033-3047. doi: 10.1093/plphys/kiae520.
Mitogen-activated protein kinases (MAPKs/MPKs) are pivotal regulators in many stress-signaling pathways in plants. The dual phosphorylation of the TXY motif by MAP kinase kinases (MKKs) is essential for activating MAPKs. Here, we reveal a mechanism for MAPK activation that bypasses the need for MKKs. We identified rice (Oryza sativa) calcium-dependent protein kinase 5 (OsCPK5) and OsCPK13 as positive regulators in salt stress tolerance. These kinases are essential for the full activation of OsMPK3 and OsMPK6 in response to elevated sodium levels, with both OsMPK3 and OsMPK6 also acting as positive regulators in rice salt tolerance. Biochemical analysis demonstrated that OsCPK5/13 directly interact with and activate OsMPK3/6 by phosphorylating the TXY motif in vitro and in vivo. Additionally, we have discovered that OsCPK5/13 relocate from the cell membrane to the nucleus in response to salt stress. This process relies on their N-terminal myristoylation and a calcium-dependent phosphorylation event within the N-terminus. Our results elucidate a MAPK activation pathway in rice that is independent of traditional MKK-mediated phosphorylation, highlighting the crucial roles of OsCPK5 and OsCPK13 in directly phosphorylating and activating OsMPK3/6, which are important for rice tolerance to salt stress.
丝裂原活化蛋白激酶（MAPKs/MPKs）是植物许多应激信号通路中的关键调节因子。MAP激酶激酶（MKKs）对TXY基序的双重磷酸化对于激活MAPKs至关重要。在此，我们揭示了一种绕过对MKKs需求的MAPK激活机制。我们鉴定出水稻（Oryza sativa）钙依赖性蛋白激酶5（OsCPK5）和OsCPK13是盐胁迫耐受性的正向调节因子。这些激酶对于响应钠水平升高时OsMPK3和OsMPK6的完全激活至关重要，OsMPK3和OsMPK6在水稻耐盐性中也作为正向调节因子发挥作用。生化分析表明，OsCPK5/13在体外和体内通过磷酸化TXY基序直接与OsMPK3/6相互作用并激活它们。此外，我们发现OsCPK5/13响应盐胁迫从细胞膜重新定位到细胞核。这个过程依赖于它们的N端肉豆蔻酰化和N端内的钙依赖性磷酸化事件。我们的结果阐明了水稻中一条独立于传统MKK介导的磷酸化的MAPK激活途径，突出了OsCPK5和OsCPK13在直接磷酸化和激活OsMPK3/6中的关键作用，这对水稻耐盐性很重要。
