MKK4/MKK5-MPK1/MPK2 cascade mediates SA-activated leaf senescence via phosphorylation of NPR1 in Arabidopsis

• Published in: Plant molecular biology Vol. 102; no. 4-5; pp. 463 - 475
• Main Authors: Zhang, Jianjian, Gao, Jiong, Zhu, Zheng, Song, Yi, Wang, Xiaoyan, Wang, Xiaolei, Zhou, Xin
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.03.2020; Springer Nature B.V
• Subjects: Arabidopsis; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Biochemistry; Biomedical and Life Sciences; Defective mutant; Disease resistance; Gene Expression Regulation, Plant; Isochorismate synthase; Kinases; Leaves; Life Sciences; MAP kinase; MAP Kinase Signaling System; Mitogen-Activated Protein Kinase Kinases - metabolism; Mitogen-Activated Protein Kinases - metabolism; Phosphorylation; Plant Leaves - enzymology; Plant Leaves - genetics; Plant Pathology; Plant Sciences; Plants, Genetically Modified - genetics; Protein kinase; Salicylic acid; Salicylic Acid - pharmacology; Senescence; Signal Transduction; NPR1; SA; Probenazole; MAPKs
• ISSN: 0167-4412; 1573-5028
• DOI: 10.1007/s11103-019-00958-z

The mechanism by which endogenous salicylic acid (SA) regulates leaf senescence remains elusive. Here we provide direct evidence that an enhancement of endogenous SA level, via chemical-induced upregulation of ISOCHORISMATE SYNTHASE 1 ( ICS1 ), could significantly accelerate the senescence process of old leaves through mediation of the key SA signaling component NON EXPRESSOR OF PATHOGENESIS RELATED GENES 1 (NPR1) in Arabidopsis . Importantly, by taking advantage of this chemically induced leaf senescence system, we identified a mitogen-activated protein kinase (MAPK) cascade MKK4/5-MPK1/2 that is required for the SA/NPR1-mediated leaf senescence. Both MKK4/5 and MPK1/2 exhibited SA-induced kinase activities, with MPK1/2 being the immediate targets of MKK4/5. Double mutants of mkk4 mkk5 and mpk1 mpk2 displayed delayed leaf senescence, while constitutive overexpression of the kinase genes led to premature leaf senescence. Such premature leaf senescence was suppressed when they were overexpressed in an SA synthesis defective mutant ( sid2 ) or signaling detective mutant ( npr1 ). We further showed that MPK1, but not MPK2, could directly phosphorylate NPR1. Meanwhile, MPK1 also mediated NPR1 monomerization. Notably, induction of disease resistance was significantly compromised in the single and double mutants of the kinase genes. Taken together, our data demonstrate that the MKK4/5-MPK1/2 cascade plays a critical role in modulating SA signaling through a complex regulatory network in Arabidopsis . Key message We reveal a MAPK cascade, MKK4/5-MPK1, which not only phosphorylates the key SA signaling component NPR1 specifically, but also regulates its oligomer-to-monomer conformational change somehow via mediation of TRX-h3/5 .