title: 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.
authors.affiliation: Department of Biology, Plant Physiology and Molecular Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Marjaana
authors.initials: M
authors.lastname: Suorsa
authors.forename: Sari
authors.initials: S
authors.lastname: Sirpiö
authors.forename: Yagut
authors.initials: Y
authors.lastname: Allahverdiyeva
authors.forename: Virpi
authors.initials: V
authors.lastname: Paakkarinen
authors.forename: Fikret
authors.initials: F
authors.lastname: Mamedov
authors.forename: Stenbjörn
authors.initials: S
authors.lastname: Styring
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
mesh_terms: D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D008027:Light; D016254:Mutagenesis, Insertional; D009876:Operon; D010100:Oxygen / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000235:genetics* / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D045332:Photosystem II Protein Complex; C508087:PsbR protein, Arabidopsis; D010100:Oxygen