Photosystem vulnerabilities under compound abiotic stresses: mechanisms, diagnostics, and engineering for resilient crops

• Identifies PSI/PSII asymmetries under compound stresses. • Details NPQ subtypes and diagnostic metrics. • Proposes hierarchical prevention for crop resilience. • Advocates feasible synthetic biology innovations. Photosynthesis, essential for plant productivity and global food security, is vulnerable to compound abiotic stresses like high light, drought, heat, and salinity. These disrupt Photosystem II (PSII) and Photosystem I (PSI), causing efficiency losses and yield declines. We reframe vulnerabilities via architectural asymmetries (rapid D1 turnover in PSII vs. slow Fe–S repair in PSI) and multifaceted protective mechanisms, including non-photochemical quenching (NPQ) subtypes (qE, qT, qZ, qH, qI), cyclic electron transport (CEF), and photosynthetic control (PhotCon). Mapping "ROS geography" emphasizes acceptor side over reduction (Mehler-driven Fe–S damage) and donor side imbalances (¹O ₂ -mediated P700 oxidation), with metrics like Y(NA), Y(ND), and EPR for phenotyping. Using cryo-EM and genetic models, we link mechanisms to assays (e.g., NPQ relaxation kinetics) to resolve debates, such as Y(ND)'s sufficiency for PhotCon. Based on evolutionary principles, we propose a hierarchical prevention framework from sensing to proteostasis and advocate synthetic plastid engineering with digital twins and optogenetic CEF/NPQ switches. This empowers development of antifragile crops adapting to climate variability, enhancing food security.