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

Abstract

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 S 2 and S 3 oxidation states (Liu, H., Frankel, L. K., and Bricker, T. M. (2007) Biochemistry 46, 7607-7613). In this study, we have documented that the S 2 and S 3 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 S 2 and S 3 state decay. The oxygen-evolving complexes of the mutant did, however, exhibit somewhat enhanced stability following this treatment. Incubation with CaCl 2 had a significantly more dramatic effect. Under this condition, both the S 2 and S 3 states of the mutant decayed at nearly the same rate as the wild type, and the total oxygen yield and its stability following CaCl 2 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. Photosystem II (PS II)2 functions as a light-driven, waterplastoquinone oxidoreductase. In higher plants and cyanobacteria at least six intrinsic proteins appear to be required for O 2 evolution (1-3). These are CP47, CP43, D1, D2, and the ␣ and ␤ subunits of cytochrome b 559 . Deletion of these subunits uniformly results in the loss of PS II function and assembly (4). Additionally, in higher plants, three extrinsic proteins, with apparent molecular masses of 33 kDa (PsbO), 24 kDa (PsbP), and 16 kDa (PsbQ), are also required for maximal rates of O 2 evolution at physiological inorganic cofactor concentrations. Of these three proteins, the PsbO protein appears to play a central role in the stabilization of the manganese cluster, is essential for efficient and stable O 2 evolution, and is required, along with PsbP, for photoautotrophic growth and PS II assembly in higher plants propagated under normal growth conditions (5, 6).In Arabidopsis thaliana, two genes that encode PsbO (psbO-1, At5g66570 and psbO-2, At3g50820) are normally expressed, yielding two different PsbO proteins (PsbO-1 and PsbO-2, respectively). A highly fluorescent mutant, psbo1, was recently identified in which a stop codon has been introduced in the psbO-1 gene by ethane methylsulfonate mutagenesis at amino acid residue ...

Probing the topography of the photosystem II oxygen evolving complex: PsbO is required for efficient calcium protection of the manganese cluster against dark-inhibition by an artificial reductant

“…This conclusion is consistent with the results of the experiments on cyanobacterial PSII (Loll et al 2005) that were interpreted to indicate that the Ca 2? binding site is created upon binding of PsbO to PSII, and with recent work by Bricker and Frankel (2008) that showed inefficient retention of Ca 2? in an A. thaliana mutant lacking PsbO-1, but not the PsbO-2 protein.…”

Molecular Functions of Oxygen‐Evolving Complex Family Proteins in Photosynthetic Electron Flow

“…However, the total PsbO level in psbo1 mutant never reaches the level observed in the wild type, which results in the lower PSII activity in psbo1. In addition, functional defect of the PsbO2 protein itself has been suggested (Murakami et al 2005; Liu et al 2007; Bricker and Frankel 2008; Allahverdiyeva et al 2009). It was also reported that PsbO2 might have a specialized function in PSII repair (Lundin et al 2007).…”

The Evolutionarily Conserved Protein PHOTOSYNTHESIS AFFECTED MUTANT71 is Required for Efficient Manganese Uptake at the Thylakoid Membrane in Arabidopsis

“…There are two distinct isoforms in Arabidopsis, PsbO1 and PsbO2, with the PsbO1 isoform being by far the more abundant of the two (Murakami et al, 2002). The psbo1 mutant exhibits a distinctive phenotype, with pale-green leaves, reduced rosette size, and slower growth rate, which underlines the importance of the PsbO1 isoform for the structure and function of PSII (Murakami et al, 2002;Lundin et al, 2007;Bricker and Frankel, 2008;Allahverdiyeva et al, 2009).…”