Light intensity and quality stimulated Deg1-dependent cleavage of PSII components in the chloroplasts of maize.

Recent studies have revealed that photo damages inducing high white light illumination of C3-type plant Arabidopsis thaliana promotes Deg1-mediated degradation of not only photosystem II core proteins D1/D2 but also minor LHCII proteins CP26, CP29 and PSII-associated PsbS protein. Using biochemical and immunological approaches we show that that the substrate pool of the heterologously expressed Deg1 ortholog protease from C4-type plant Zea mays is very similar to that of the A. thaliana in both mesophyll and bundle sheath chloroplasts. The Deg1-mediated degradation of photosystem II components has been observed after high light and red light treatment of maize leaves, while far red light did not induce Deg1-mediated degradation. Moreover, two isoforms of the Deg1 protease have been identified. Their genes are localized in chromosomes 6 and 8. The Pull-Down assay indicated that both proteins were able to bind the same set of chloroplast proteins, nevertheless in vitro digestion of Z. mays thylakoids in the form of inside-out vesicles has raveled that only Deg1 found in chromosome 8 exhibited proteolytic activity. Interestingly, the relative amount of Deg1 proteases in Z. mays bundle sheath chloroplasts (BS) is significantly higher than in mesophyll chloroplasts (M) in spite of lower content of PSII (∼20%) in BS.