Multi-Subunit Engineering of Photorespiratory Glycine Decarboxylase Refines Photosynthesis, Growth and Metabolic...

Photorespiration secures oxygenic photosynthesis from metabolic constraints arising from the oxygenation reaction of Rubisco in today's oxygen-rich atmosphere. Beyond this protective function, it is vital for primary metabolism, cellular redox balance, and stomatal regulation. Importantly, photorespiration has emerged as a key target for improving CO₂ assimilation and biomass production. Among proposed strategies, enhancing photorespiratory efficiency via upregulation of core enzymes has highlighted glycine decarboxylase (GDC) as a promising target, however, it remains unclear whether simultaneous upregulation of multiple GDC components would yield additive or synergistic improvements in plant environmental acclimation. Here, we systematically compared single and double GDC overexpression lines under varying photoperiods, elevated oxygen and high light. GDC upregulation consistently promoted growth across photoperiods and enhanced photosynthetic performance under high light and oxygen, indicating a severe benefit of increased photorespiratory metabolite conversion. Notably, double overexpression lines exhibited enhanced metabolic flexibility beyond that observed in single lines, supporting synergistic effects on carbon assimilation and allocation. Short-term high-light exposure further revealed increased Rubisco activity and efficient partitioning of carbon into sucrose and starch. Collectively, our results demonstrate that coordinated enhancement of GDC activity strengthens photorespiratory efficiency and can generate synergistic improvements in photosynthetic robustness, metabolic robustness, and environmental acclimation under stressful conditions. These findings position multicomponent GDC engineering as a promising strategy for developing crops with improved environmental acclimation capacity.