Design Principles of Plant Thermotolerance: Integrating Photosynthesis, Reproduction, and Field Resilience in a Warming Climate.

Global food security is increasingly threatened by climate change, as rising temperatures compromise the yields of major staple crops, including wheat, rice, and maize. Enhancing plant thermotolerance has therefore become a critical priority for sustaining agricultural productivity. However, plant heat-stress responses have often been described as fragmented and pathway-specific, limiting their translation into effective crop improvement strategies. Here, we synthesize current knowledge of plant responses to heat stress and reframe them as an integrated set of design principles centered on preserving photosynthetic carbon gain under high temperature. By doing so, we provide a collection of insights that may help guide future research efforts and the development of strategies for improving plant thermotolerance. We organize major defense strategies into six functional domains: (i) membrane systems and structural integrity, (ii) photosynthetic regulation, (iii) protective metabolites and hormonal signaling, (iv) reactive oxygen species (ROS) scavenging, (v) protein homeostasis, and (vi) transcriptional and post-transcriptional regulation. Rather than treating these responses as independent pathways, we emphasize their temporal hierarchy, energetic costs, and functional interconnections, highlighting their shared objective-maintaining CO2 assimilation, energy balance, and biomass accumulation as thermal damage accelerates. We further discuss how insights from mutagenesis, transgenic approaches, and targeted genetic modification can be translated into crop improvement, clarifying opportunities and trade-offs that emerge when thermotolerance is engineered at distinct physiological nodes. Together, this design-centered framework provides a unifying conceptual and practical roadmap for developing high-yielding, heat-tolerant cultivars, offering actionable guidance for sustaining crop productivity in a warming world.