Heat as a central regulator of plant responses to stress combination: insights from physiology, transcriptomics, and metabolomics

Plants in nature are increasingly exposed to complex abiotic stress combinations, driven by climate change. Among these, heat stress (HS) has emerged not simply as an additional stress factor, but as a dominant modulator that reshapes plant responses across physiological, molecular, and metabolic scales. As plant responses to stress combination cannot be extrapolated from single-stress experiments, more studies are needed to address the role of HS in stress combination. In this review, we synthesize recent advances in our understanding of how HS interacts with other abiotic stressors, such as drought, salinity, and/or high light, to generate distinct stress combination states. At the physiological level, stress combinations that include HS impose critical trade-offs in water relations, photosynthesis, and growth, often generating biological conflicts and spatially-distinguished responses, such as differential transpiration between vegetative and reproductive tissues. Transcriptomic analyses reveal that HS preserves a conserved heat-responsive transcriptomic core while simultaneously driving stress-specific transcriptional reprogramming, with a regulatory architecture that is highly species-dependent. Metabolomic studies further demonstrate that HS emerges as a dominant regulator of metabolic reconfiguration under combined stresses, promoting the accumulation of compatible solutes, sugars, amino acids, and signaling metabolites. Together, these findings highlight the central role of HS in stress combination and suggest that it is governed by hierarchical and context-dependent regulation. We further discuss the implications of these insights for improving plant resilience under realistic environmental conditions and emphasize the need for integrative, multi-scale approaches tailored to the specific ‘stress landscapes’ faced by individual crops in a warming world.