Phytohormonal crosstalk: a plant defense network in response to abiotic and biotic stresses

Plants are continuously subjected to a variety of environmental stresses, including biotic (such as herbivores and pathogens) and abiotic (such as drought, salinity, heat and cold stresses). Their ability to survive under such adverse conditions relies on highly coordinated and sophisticated phytohormonal signaling networks. Major plant hormones including abscisic acid (ABA), ethylene (ET), salicylic acid (SA), auxins, jasmonic acid (JA), gibberellins (GAs) and cytokinins (CKs) are involved in stress perception, defense mechanisms, growth, and development of plants. These hormones modulate gene expression, activate signal transduction cascades, regulate metabolic pathways and control key physiological processes such as reactive oxygen species (ROS) detoxification, osmoprotectant accumulation and stomatal movement. Evidence is accumulating that hormonal signaling pathways extensively cross-talk, enabling plants to balance growth and stress responses under unfavorable conditions. Moreover, phytohormone-mediated regulatory mechanisms are closely related with epigenetic modifications, RNA-based regulation and transcription factor networks that are involved in stress memory and priming, enabling plants to respond more quickly and efficiently to repeated stress events. This review summarizes the current knowledge of the roles of phytohormones in plant stress responses, especially their molecular mechanisms, signaling integration and hormonal interactions. Despite substantial progress, major knowledge gaps remain in understanding how interconnected hormonal networks integrate with transcriptional, epigenetic, metabolic, and redox processes, particularly under combined, fluctuating, and recurrent stresses. Future research integrating multi-omics, advanced phenotyping, systems biology, and precision breeding will be essential for resolving these context-dependent regulatory networks and translating mechanistic insights into high-yielding, climate-resilient crops.