MAPK signaling in plant metabolic control: integrating phytohormones with primary and secondary metabolism.

Abstract

Mitogen-activated protein kinase (MAPK) cascades are conserved signaling modules that integrate environmental and developmental cues to regulate plant metabolism. This review synthesizes current understanding of how MAPKKK-MAPKK-MAPK cascades coordinate primary metabolism, secondary metabolism, and phytohormone biosynthesis. MAPK cascades regulate photosynthetic capacity, nitrogen fixation and assimilation, and carbon flux through phosphorylation of key metabolic enzymes and transcription factors that balance growth with stress responses. In secondary metabolism, MAPK cascades converge on downstream transcription factors to regulate camalexin, indole glucosinolate, phenylpropanoid, flavonoid, lignin, terpenoid, and alkaloid biosynthesis. We further summarize how MAPKs are involved in the biosynthesis and signaling of ethylene, jasmonic acid, salicylic acid, auxin, and abscisic acid, revealing extensive crosstalk between kinase cascades and hormonal networks. We propose an integrative model in which MAPK cascades function as signaling hubs funneling upstream cues into three coordinated arms: transcription factor phosphorylation, direct modulation of structural enzymes, and phytohormone crosstalk. Future research should address key knowledge gaps, including incomplete MAPK cascades, limited understanding of MAPK substrates and their specificity in metabolic regulation, feedback mechanisms preventing metabolic overactivation, and the conservation of these principles across crop species. Understanding MAPK-mediated metabolic control holds promise for engineering stress-resilient, pathogen-resistant, and high-yield crops.

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