The chloroplast DegP2 protease is down regulated in response to pathogen attack

Abstract

Although light is the ultimate substrate in photosynthesis it can also be harmful and lead to oxidative damage of the photosynthetic apparatus. The main target for light stress is the photosystem II (PSII) and its D1 reaction centre protein. Degradation of the photodamaged D1 protein and its rapid replacement by a de novo synthesised functional copy represents the important repair mechanism of PSII. Recently, we isolated a single copy nuclear gene from Arabidopsis thaliana, encoding a protease that performs GTP-dependent primary cleavage of the photodamaged D1 protein. This protease, designated DegP2 (for second DegP described from the chloroplast) is a member of a large family of related Deg/Htr serine endopeptidases, which are found in most organisms including bacteria, humans and plants. Database searches revealed that 13 different Deg/Htr protease homologues, with various subcellular locations, are present in A. thaliana plants. Topology studies revealed that DegP2 is peripherally associated with the outer surface of the non-appressed region of the thylakoid membrane. Expression studies demonstrated that this enzyme is expressed in photosynthetically active tissues and its level is strongly diminished during natural plant senescence and after pathogen attack.