Endophyte function in climate-stressed crops: integrating molecular regulation, metabolic trade-offs, and ecological constraints.

Climate change increasingly exposes crops to simultaneous abiotic and biotic stresses, disrupting physiological stability and reducing agricultural productivity. Although endophytes are widely recognized for improving plant stress tolerance, their effectiveness remains inconsistent across environmental conditions. This review develops an integrative framework to explain how endophyte-mediated responses are regulated at the molecular, metabolic, and ecological levels under climate stress. We examine multi-level interactions to inform predictive deployment in varied agricultural environments. We critically synthesize recent studies on ROS-hormone signaling, carbon allocation trade-offs, metabolic reprogramming, microbiome interactions, ecological filtering, and host genotype-dependent responses. We aim to identify mechanisms that govern the stability or destabilization of plant-endophyte associations under stress conditions. The analysis indicates that endophyte-mediated beneficial traits remain effective only when redox regulation, metabolic balance, and ecological compatibility are maintained within functional physiological limits. Under severe or prolonged stress, disruption of ROS homeostasis, carbon limitation, and ecological instability progressively reduce symbiotic effectiveness, physiological stability, and plant growth performance. Potential predictive variables in this framework include ROS accumulation thresholds, antioxidant capacity, photosynthetic stability, carbon allocation balance, and ecological persistence of endophytes under fluctuating environmental conditions. These variables may enable the prediction of endophyte functional stability, stress adaptation, and growth promotion under heterogeneous climate stress conditions. Collectively, this framework advances current understanding from descriptive interpretation toward a context-dependent perspective that may support future prediction and validation of endophyte performance in climate-resilient agriculture.