Horticultural and medicinal plants are important for their economic and pharmacological value; however, their quality traits are severely affected by abiotic stresses. The mitogen-activated protein kinase (MAPK) cascade is an evolutionarily conserved signaling module that links abiotic stress signals to the regulation of plant quality traits. While the roles of MAPKs in growth, phytohormone signaling, and immunity are well established, a comprehensive review that integrates MAPK functions in abiotic stress responses and secondary metabolism, particularly in horticultural and medicinal plants, is still lacking. In this review, we systematically summarize (i) the composition, classification, and phylogenetic relationships of MAPKs in horticultural and medicinal plants; (ii) their mechanistic involvement in abiotic stress responses, particularly to salt, drought, and extreme temperatures; (iii) recent advances in understanding how MAPK-mediated signaling governs secondary metabolite accumulation; and (iv) a unified framework that presents MAPKs as a key bridge between stress responses and metabolic reprogramming. These insights provide a foundation for MAPK-targeted breeding and engineering strategies that enhance stress tolerance and improve quality traits in horticultural and medicinal plants through precise pathway manipulation.

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