Regulation of energy production and photoprotection in photosynthesis: Theories, mechanisms, and Implications for crop improvement.

The light-dependent reactions of photosynthesis are fundamental to driving electron and proton fluxes, which are essential for the production of ATP and reductants, while simultaneously providing critical photoprotection. As both energy generation and photoprotection have become key targets in efforts to improve crop yield potential, making the regulation of light reactions-particularly energy balance-a topic of great importance. This review synthesizes current and past understanding of these processes. We begin by highlighting the discrepancy between the output of linear electron flow (LEF) and the demand for CO2 fixation during photosynthesis. Subsequently, we explore the mechanisms that enhance ATP production and photoprotection, both independently and synergistically. A particular focus is placed on energy-dependent quenching (qE) as a central photoprotective response, followed by an analysis of stress-induced photodamage and photoinhibition to photosystem II when photoprotective capacity is insufficient. Finally, we discuss an important question: Does breeding for yield potential through manipulating these light-dependent processes enhance crop climate adaptation? This underexplored topic offers novel insights and potential directions for developing crop varieties with enhanced resilience to fluctuating environmental conditions.