Phytohormone-microbiome interactions and epigenetic regulation of plant stress responses and priming.

Plants continuously face fluctuating environmental conditions, requiring tightly coordinated regulatory systems to balance growth and stress responses. This review synthesizes current knowledge on phytohormones as central integrators of plant-microbiome interactions, highlighting their dual role as internal regulators and ecological gatekeepers that shape microbiome assembly and function. Phytohormones, such as auxins, cytokinins, gibberellins, abscisic acid, ethylene, salicylic acid, and jasmonates, dynamically regulate plant development, immunity, and rhizosphere chemistry, thereby influencing microbial recruitment and activity. In turn, plant-associated microbes actively modulate hormonal pathways through biosynthesis, degradation, and interference with signaling and transport processes, thereby reconfiguring plant physiological responses. Emerging evidence demonstrates that these interactions underpin microbial priming, enabling enhanced responsiveness to subsequent stresses without constitutive defense costs. Such primed states are frequently associated with epigenetic modifications, including DNA methylation and histone modifications, which contribute to stress memory and may persist across generations. We propose that microbiome-driven hormonal regulation represents a key mechanism for plant adaptation to environmental stress and that its integration can offer promising opportunities to enhance resilience, reduce agrochemical dependence, and improve agricultural sustainability under climate change.