A chloroplast DegP2 protease performs the primary cleavage of the photodamaged D1 protein in plant photosystem II

Although light is the ultimate substrate in photosynthesis, it can also be harmful and lead to oxidative damage of the photosynthetic apparatus, The m ain target for light stress is the central oxygen-evolving photosystem II ( PSII) and its D1 reaction centre protein. Degradation of the damaged D1 pro tein and its rapid replacement by a de novo synthesized copy represent the important repair mechanism of PSII crucial for plant survival under light s tress conditions, Here we report the isolation of a single-copy nuclear gen e from Arabidopsis thaliana, encoding a protease that performs GTP-dependen t primary cleavage of the photodamaged D1 protein and hence catalysing the key step in the repair cycle in plants. This protease, designated DegP2, is a homologue of the prokaryotic Deg/Htr family of serine endopeptidases and is associated with the stromal side of the non-appressed region of the thy lakoid membranes. Increased expression of DegP2 under high salt, desiccatio n and light stress conditions was measured at the protein level.