Abstract: Photorespiration is essential for maintaining plant photosynthesis and growth under aerobic conditions. While environmental factors like light–dark transitions and high light modulate this pathway, the underlying molecular regulatory mechanisms remain unclear. Here, we report that the activity of phosphoglycolate phosphatase (PGLP), the first enzyme in the photorespiratory pathway, is redox-regulated in response to environmental light conditions. Specifically, Arabidopsis PGLP enzymatic activity enhanced under reducing conditions and light, but suppressed under oxidative conditions and darkness. Light–dark transitions dynamically alter the oligomeric state of PGLP1, as darkness promotes oligomer assembly, while light triggers disassembly, a process critically dependent on cysteine 320 (Cys320) of PGLP1. Thioredoxin (Trx) f directly interacts with PGLP1, modulating both; its light-dependent oligomeric state and enzymatic activity. Complementation of the Arabidopsis pglp1-2 mutant with wild-type PGLP1 or the Cys320 mutant (C320S) revealed that C320S-complemented lines show greater tolerance to high-light and fluctuating light conditions. Collectively, our study identifies a redox-dependent post-translational modification mechanism that fine-tunes PGLP activity, thereby optimizing photorespiratory metabolism to enhance plant photosynthetic efficiency and environmental adaptability.

Key words: phosphoglycolate phosphatase, photorespiration, photosynthesis, redox modification, thioredoxin f