Abstract: Heat stress (HS) is becoming a major and constant threat to crop production and food security as global warming progresses. Consequently, understanding and improving crop tolerance to HS are currently among the most important targets in plant biology and breeding research (Langridge and Reynolds.2021). Recent evidences suggest epigenetic mechanisms act as new layer of regulation to cope with HS (Ohama et.al.2017; Song et.al.2021). However, the specific regulatory module composed of epigenetic factor and transcription factor in establishing thermotolerance remains unclear. As a typical cool-season crop, wheat is vulnerable to HS, especially at the flowering and grain-filling stages (Kaur et.al.2019). Here, we report that TaHAG1 plays a pivotal role in thermotolerance by maintaining the photosynthetic stability in wheat.(Plant Biotechnology Journal)