Coral reefs are critical to marine biodiversity, supporting approximately 25% of marine species and a $2.7 trillion global economy, including fishing and tourism. However, coral bleaching, driven by rising ocean temperatures, threatens ocean ecosystems. Bleaching occurs when thermal stress forces coral to expel their symbiotic algae, Symbiodinium (Zooxanthellae). These algae are crucial for coral survival as they provide energy, disease protection, and vibrant coloration – critical for photosynthesis and UV protection. Without these algae, corals become vulnerable to disease and death. As of 2024, 77% of corals have experienced bleaching-level heat stress, with temperatures projected to rise by 2.4 C° by 2050. Current strategies such as reef-safe sunscreens, carbon-sequestration seagrass, and emission cuts offer localized relief but don’t tackle coral heat resistance directly. Our design boosts coral heat tolerance by transferring heat shock proteins (HSPs) from Arabidopsis thaliana into Symbiodinium. HSPs are proteins that maintain cellular homeostasis under stress, protecting against thermal damage by folding and repairing damaged proteins, preventing cellular dysfunction. A. thaliana exhibits advanced HSP mechanisms, including high oxidative stress management and protein repair, making its HSPs ideal candidates for boosting Symbiodinium heat resistance. Our approach offers a scalable method to increase coral resilience to rising ocean temperatures by strengthening the coral at a cellular level. Unlike short-term emission reductions, our solution strengthens coral biology by enhancing heat resistance mechanisms. This approach reduces thermal stress on Symbiodinium and promotes long-term coral survival, boosting marine ecosystem health and the global economies reliant on healthy reefs.