Phytohormonal regulation of photosynthesis in response to light stress

• Light stress causes photoinhibition, oxidative stress, and diminishes photosynthetic efficiency and crop yield. • Phytohormones regulate chloroplast activity and redox homeostasis. • ABA and JA enhance antioxidant defences and anthocyanin accumulation. • GAs, auxins, and BRs optimize light capture under shade stress. Light is essential for photosynthesis, but both high and low irradiance disturb the balance between energy absorption and utilization, leading to photoinhibition, oxidative stress, and reduced productivity. Plants mitigate these challenges through phytohormonal regulation that coordinates chloroplast activity, redox homeostasis, and transcriptional adjustment. Although often overlooked compared to drought or salinity, light stress is a critical abiotic factor that directly limits photosynthetic efficiency and crop yield. This review synthesizes current advances in understanding how phytohormones including, auxins, cytokinins (CKs), gibberellins (GAs), abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), brassinosteroids (BRs), ethylene, and strigolactones (SLs) modulate photosynthesis and photoprotection under high- and low-light stress. Under high light, ABA and JA enhance antioxidant defenses, non-photochemical quenching, and anthocyanin accumulation, while CKs help maintain photosynthetic efficiency through chloroplast development and PSII repair. Under low light, GAs and auxins promote stem elongation and leaf expansion to optimize light capture, BRs enhance chlorophyll synthesis and carbon metabolism, and ethylene with ABA regulate leaf angle and shoot–root balance. These phytohormonal responses are integrated by transcriptional networks, chromatin modifications, and small RNA pathways, enabling both short-term protection and long-term acclimation. Future research should focus on phytohormone–epigenome interactions, phytohormone–miRNA crosstalk, and cell-specific responses. Linking mechanistic knowledge with breeding and management will enable strategies to enhance photosynthetic efficiency and resilience under variable light conditions by climate change.