TaUSP_6D-5 integrates light signalling and heat stress to regulate thermotolerance and developmental transitions in plants.

Universal Stress Proteins (USPs) constitute a conserved class of stress-responsive proteins that play important roles in helping plants adapt to adverse environmental conditions, including heat, oxidative stress, and endoplasmic reticulum (ER) stress. However, the molecular mechanisms through which USPs integrate environmental and developmental signalling pathways remain poorly understood. In this study, we characterized the wheat Universal Stress Protein TaUSP_6D-5 and identified it as a potential link between light signalling and thermotolerance. Our results demonstrated that TaUSP_6D-5 is localized to the endoplasmic reticulum and interacts with a wheat Annexin protein, suggesting a role in stress-associated cellular signalling. Overexpression of TaUSP_6D-5 in Arabidopsis thaliana enhanced thermotolerance and reduced reactive oxygen species (ROS) accumulation under heat stress conditions. Promoter analysis further revealed that TaUSP_6D-5 expression is induced independently by ER stress and far-red light treatment. Moreover, transgenic Arabidopsis plants overexpressing TaUSP_6D-5 displayed enhanced hypocotyl elongation in darkness along with altered expression of AtPIF transcripts, indicating its involvement in light-responsive developmental processes. Collectively, these findings suggest that TaUSP_6D-5 functions at the convergence of light and high-temperature signalling pathways and contributes to stress adaptation and environmental signal perception in plants.