Mechanism of REP27 Protein Action in the D1 Protein Turnover and Photosystem II Repair from Photodamage    

Abstract

The function of the REP27 protein (GenBank accession no. EF127650) in the photosystem II (PSII) repair process was elucidated. REP27 is a nucleus-encoded and chloroplast-targeted protein containing two tetratricopeptide repeat (TPR) motifs, two putative transmembrane domains, and an extended carboxyl (C)-terminal region. Cell fractionation and western-blot analysis localized the REP27 protein in the Chlamydomonas reinhardtii chloroplast thylakoids. A folding model for REP27 suggested chloroplast stroma localization for amino-and C-terminal regions as well as the two TPRs. A REP27 gene knockout strain of Chlamydomonas, termed the rep27 mutant, was employed for complementation studies. The rep27 mutant was aberrant in the PSII-repair process and had substantially lower than wild-type levels of D1 protein. Truncated REP27 cDNA constructs were made for complementation of rep27, whereby TPR1, TPR2, TPR1+TPR2, or the C-terminal domains were deleted. rep27-complemented strains minus the TPR motifs showed elevated levels of D1 in thylakoids, comparable to those in the wild type, but the PSII photochemical efficiency of these strains was not restored, suggesting that the functionality of the PSII reaction center could not be recovered in the absence of the TPR motifs. It is suggested that TPR motifs play a role in the functional activation of the newly integrated D1 protein in the PSII reaction center. rep27-complemented strains missing the C-terminal domain showed low levels of D1 protein in thylakoids as well as low PSII photochemical efficiency, comparable to those in the rep27 mutant. Therefore, the C-terminal domain is needed for a de novo biosynthesis and/or assembly of D1 in the photodamaged PSII template. We conclude that REP27 plays a dual role in the regulation of D1 protein turnover by facilitating cotranslational biosynthesis insertion (C-terminal domain) and activation (TPR motifs) of the nascent D1 during the PSII repair process.

Effect of cadmium on photosystem II activity in Chlamydomonas reinhardtii: alteration of O–J–I–P fluorescence transients indicating the change of apparent activation energies within photosystem II

“…To determine protein content in samples treated with Cd, we used determined amount of Chl (0.5 mg total Chl loaded on the gel) as in Dewez et al (2009). Thylakoids of control and cadmium-treated cells were isolated using glass beads and resuspended in isolation buffer (50 mM tricine, 10 mM NaCl, 5 mM MgCl 2 , pH 7.8) (Morgan et al 1998).…”

HYPERSENSITIVE TO HIGH LIGHT1 Interacts with LOW QUANTUM YIELD OF PHOTOSYSTEM II1 and Functions in Protection of Photosystem II from Photodamage in Arabidopsis

“…Presumably, therefore, the roles of these factors in PSII biogenesis or maintenance have been retained during evolution. In contrast, other factors are specific to cyanobacteria, such as PROCESSING ASSOCIATED TPR PRO-TEIN (Schottkowski et al, 2009), Slr0286 (Kufryk and Vermaas, 2001), and Slr2013 (Kufryk and Vermaas, 2003), or specific to higher plants, such as LOW PSII ACCUMULATION1 (LPA1)/PSII REPAIR27 (Park et al, 2007;Dewez et al, 2009) and LPA2 , which may represent evolutionary adaptations to specific environments. Notably, LOW QUANTUM YIELD OF PHOTOSYNSTEM II1 (LQY1), a small thylakoid zinc-finger protein exclusive to land plants, was also recently found to be involved in the repair cycle and reassembly of PSII .…”

The Arabidopsis Thylakoid Protein PAM68 Is Required for Efficient D1 Biogenesis and Photosystem II Assembly

“…HCF136 predominantly associates with a very early PSII assembly complex containing D2, PsbE, and PsbF (Plü cken et al, 2002), and YCF48, the Synechocystis HCF136 homolog, has been detected in RC, where it interacts with unassembled pD1 (Komenda et al, 2008). In Arabidopsis, LPA1 binds to D1 during de novo biogenesis of PSII (Peng et al, 2006), whereas its Chlamydomonas ortholog, REP27, has also been suggested to play a role in D1 synthesis, albeit during PSII repair rather than during assembly (Park et al, 2007;Dewez et al, 2009). The Arabidopsis LPA2, which has no counterpart in cyanobacteria or Chlamydomonas, interacts specifically with CP43 and ALB3 (Ma et al, 2007).…”