The psbo1 Mutant of Arabidopsis Cannot Efficiently Use Calcium in Support of Oxygen Evolution by Photosystem II

• Published in: The Journal of biological chemistry Vol. 283; no. 43; pp. 29022 - 29027
• Main Authors: Bricker, Terry M., Frankel, Laurie K.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 24-10-2008; American Society for Biochemistry and Molecular Biology
• Subjects: Arabidopsis - metabolism; Binding Sites; Calcium - metabolism; Calcium Chloride - chemistry; Metabolism and Bioenergetics; Models, Biological; Mutation; Oxygen - chemistry; Oxygen - metabolism; Photosynthetic Reaction Center Complex Proteins - chemistry; Photosystem II Protein Complex - genetics; Photosystem II Protein Complex - physiology; Protein Binding; Thylakoids - metabolism; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M805122200

The Arabidopsis thaliana mutant psbo1 contains a point mutation in the psbO-1 gene (At5g66570) leading to the loss of expression of the PsbO-1 protein and overexpression of the PsbO-2 protein (Murakami, R., Ifuku, K., Takabayashi, A., Shikanai, T., Endo, T., and Sato, F. (2002) FEBS Lett. 523, 138–142). Previous characterization of fluorescence induction and decay kinetics by our laboratory documented defects on both the oxidizing and reducing sides of Photosystem II. Additionally, anomalous flash oxygen yield patterns indicated that the mutant contains a defective oxygen-evolving complex that appears to exhibit anomalously long-lived S2 and S3 oxidation states (Liu, H., Frankel, L. K., and Bricker, T. M. (2007) Biochemistry 46, 7607–7613). In this study, we have documented that the S2 and S3 states in psbo1 thylakoids decay very slowly. The total flash oxygen yield of the psbo1 mutant was also significantly reduced, as was its stability. Incubation of psbo1 thylakoids at high NaCl concentrations did not increase the rate of S2 and S3 state decay. The oxygen-evolving complexes of the mutant did, however, exhibit somewhat enhanced stability following this treatment. Incubation with CaCl2 had a significantly more dramatic effect. Under this condition, both the S2 and S3 states of the mutant decayed at nearly the same rate as the wild type, and the total oxygen yield and its stability following CaCl2 treatment were indistinguishable from that of the wild type. These results strongly suggest that the principal defect in the psbo1 mutant is an inability to effectively utilize the calcium associated with Photosystem II. We hypothesize that the PsbO-2 protein cannot effectively sequester calcium at the oxygen-evolving site.