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AtMPK1/AtMPK2 Interact with AtVQ25 to Enhance Its Protein Stability and Coordinately Regulate Salicylic Acid-Mediated
Qi Tan1,2, Mengwei Zhang1, Yujia Song1
1Ministry of Education Key Laboratory of Molecular and Cellular Biology, Hebei Research Center of the Basic Discipline of Cell Biology, Hebei Collaboration Innovation Center for Cell Signaling and Environmental Adaptation, Hebei Key Laboratory of Molecular and Cellular Biology, College of Life Sciences, Hebei Normal University, Shijiazhuang 050024, China.
Abstract:
Leaf senescence is a pivotal developmental program in plants, precisely regulated by diverse signals including salicylic acid (SA). The Arabidopsis VQ protein AtVQ25 has been previously characterized as a positive regulator of SA-mediated leaf senescence, functioning through interaction with AtWRKY53 to relieve the transcriptional self-repression of AtWRKY53 at its own promoter. However, the upstream regulatory mechanisms governing AtVQ25 itself remain elusive. In this study, a yeast library screening was performed, and the mitogen-activated protein kinases AtMPK1 and AtMPK2 were identified as interacting partners of AtVQ25. The direct physical interaction was validated by yeast two-hybrid (Y2H), luciferase complementation imaging (LCI), pull-down, and co-immunoprecipitation assays (Co-IP). Furthermore, AtVQ25 was shown to be directly phosphorylated by AtMPK1/AtMPK2, which enhanced its protein stability and retarded its degradation, thereby positively modulating leaf senescence progression. Genetic analyses revealed that the function of AtVQ25 in SA-mediated leaf senescence depends on the functional integrity of AtMPK1/AtMPK2. Collectively, these findings establish AtMPK1/AtMPK2 as upstream interactors of AtVQ25 that coordinate SA-mediated leaf senescence through phosphorylation-dependent enhancement of AtVQ25 protein stability, providing novel insights into the upstream regulatory circuitry of VQ proteins.
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