Plant Stress Biology in a Warming World: Synergies in Abiotic and Biotic Adaptation

Plants rarely experience high temperature and pathogen attack as isolated events, yet mechanistic understanding of their interaction has developed largely from single-stress experiments. Combined heat and infection create a dynamic signalling state in which thermosensory pathways, immune receptors, phytohormones, reactive oxygen species (ROS), calcium signals, redox buffering and molecular chaperones compete for control of defence, acclimation and growth. This critical narrative review evaluates how these networks intersect, with emphasis on salicylic acid (SA), jasmonic acid (JA), ethylene (ET), abscisic acid (ABA), respiratory burst oxidase homologues, heat-shock factors and nucleotide-binding leucine-rich repeat immune receptors. Evidence indicates that warming commonly attenuates SA accumulation, pattern-triggered ROS production and several forms of nucleotide-binding leucine-rich repeat-mediated resistance, but the response is strongly dependent on genotype, pathogen lifestyle, temperature regime, stress sequence and tissue context. ROS emerge not as a simple damage marker but as a spatially organised signalling currency linking immune perception to calcium influx, mitogen-activated protein kinase activity, redox control and rapid systemic communication. Hormonal effects are similarly conditional: SA can reinforce redox-dependent immunity and thermotolerance, JA/ET can either oppose or complement SA depending on the interaction, and ABA can protect water status while constraining selected immune outputs. Recent work in Arabidopsis and rice further shows that heat-response transcriptional modules can directly reprogramme immune ROS production, revealing molecular trade-offs rather than independent pathways. The strongest evidence therefore supports a network model in which combined stress changes signalling thresholds and timing at shared regulatory nodes. Progress now requires factorial host–pathogen temperature experiments, real-time hormone and ROS measurements, spatial and single-cell approaches, genetically diverse crop panels and field-realistic heatwave trajectories. Such designs are essential for separating robust molecular principles from model-specific effects and for translating mechanistic insights into durable crop resilience.