PsbR, a Missing Link in the Assembly of the Oxygen-evolving Complex of Plant Photosystem II

Abstract

The oxygen-evolving complex of eukaryotic photosystem II (PSII) consists of three extrinsic nuclear-encoded subunits, PsbO (33 kDa), PsbP (23 kDa), and PsbQ (17 kDa). Additionally, the 10-kDa PsbR protein has been found in plant PSII and anticipated to play a role in water oxidation, yet the physiological significance of PsbR has remained obscure. Using the Arabidopsis psbR mutant, we showed that the light-saturated rate of oxygen evolution is strongly reduced in the absence of PsbR, particularly in low light-grown plants. Lack of PsbR also induced a reduction in the content of both the PsbP and the PsbQ proteins, and a near depletion of these proteins was observed under steady state low light conditions. This regulation occurred post-transcriptionally and likely involves a proteolytic degradation of the PsbP and PsbQ proteins in the absence of an assembly partner, proposed to be the PsbR protein. Stable assembly of PsbR in the PSII core complex was, in turn, shown to require a chloroplast-encoded intrinsic low molecular mass PSII subunit PsbJ. Our results provided evidence that PsbR is an important link in the PSII core complex for stable assembly of the oxygen-evolving complex protein PsbP, whereas the effects on the assembly of PsbQ are probably indirect. The physiological role of the PsbR, PsbP, and PsbQ proteins is discussed in light of their peculiar expression in response to growth light conditions.

PHOTOSYSTEM II SUBUNIT R Is Required for Efficient Binding of LIGHT-HARVESTING COMPLEX STRESS-RELATED PROTEIN3 to Photosystem II-Light-Harvesting Supercomplexes in Chlamydomonas reinhardtii

“…ami-RNA-psbr-2. Likewise, the data revealed that subunits PSBP and PSBQ were both diminished in amounts in conjunction with PSBR, in agreement with data obtained for Arabidopsis PSBR-deficient plants (Suorsa et al, 2006;Liu et al, 2009;Allahverdiyeva et al, 2013). On the other hand, other PSII core subunits or the minor core PSII light-harvesting proteins, LHCB4 and LHCB5, were not significantly altered in their protein ratios in both ami-RNA-psbr strains.…”

“…Moreover, those authors identified cross-links between PSBP and CP26. The tight interaction between PSBP and PSBR, as suggested earlier (Suorsa et al, 2006;Liu et al, 2009), is also confirmed in our study, as depletion of PSBR impacts the association of PSBP with the PSII-LHCII supercomplex (Fig. 7).…”

“…An association of PSBR with the oxygen-evolving complex has been suggested, as its presence is required for the stable assembly of PSBP with the PSII core and its absence also impacts the binding of PSBQ to the core (Suorsa et al, 2006;Liu et al, 2009). For stable association with the PSII core complex, PSBR needs the presence of PSBJ (Suorsa et al, 2006). Functionally, the depletion of PSBR protein expression decreased rates of oxygen evolution (Allahverdiyeva et al, 2007(Allahverdiyeva et al, , 2013 and quinone reoxidation (Allahverdiyeva et al, 2007).…”

“…The mature protein has a predicted 70-amino acid luminal N-terminal part and a C-terminal transmembrane span (Ljungberg et al, 1986;Lautner et al, 1988;Webber et al, 1989). An association of PSBR with the oxygen-evolving complex has been suggested, as its presence is required for the stable assembly of PSBP with the PSII core and its absence also impacts the binding of PSBQ to the core (Suorsa et al, 2006;Liu et al, 2009). For stable association with the PSII core complex, PSBR needs the presence of PSBJ (Suorsa et al, 2006).…”

Light-triggered selective nitration of PsbO1 in isolated Arabidopsis thylakoid membranes is inhibited by photosynthetic electron transport inhibitors

“…The plants were grown for 4 weeks with irrigation every 4 days with a half-strength solution of inorganic salts of Murashige and Skoog medium 6 as described previously. 1 Thylakoid membranes were isolated from the leaves of Arabidopsis plants according to the method of Suorsa et al 7 Isolated thylakoid membranes were incubated in the following suspension buffer bubbled with NO 2 for 60 min at 25 C under illumination (100 mmol photons/m 2 /s) or in the dark. The suspension buffer contained 50 mM Hepes-KOH (pH 7.0), 15 mM NaCl 2 , 5 mM MgCl 2 , and 400 mM sucrose.…”