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REP27, a Tetratricopeptide Repeat Nuclear-Encoded and Chloroplast-Localized Protein, Functions in D1/32-kD Reaction Center Protein Turnover and Photosystem II Repair from Photodamage1,[OA]:  
Umeå University, Faculty of Science and Technology, Chemistry.
2007 (English)In: Plant Physiology, Vol. 143, 1547-60 p.Article in journal (Refereed) Published
Abstract [en]

The goal of this research is elucidation of the molecular mechanism for the unique photosystem II (PSII) damage and repair cycle in chloroplasts. A frequently occurring, irreversible photooxidative damage inhibits the PSII charge separation reaction and stops photosynthesis. The chloroplast PSII repair process rectifies this adverse effect by selectively removing and replacing the photoinactivated D1/32-kD reaction center protein (the chloroplast-encoded psbA gene product) from the massive (>1,000 kD) water-oxidizing and O2-evolving PSII holocomplex. DNA insertional mutagenesis in the model organism Chlamydomonas reinhardtii was applied for the isolation and characterization of rep27, a repair-aberrant mutant. Gene cloning and biochemical analyses in this mutant resulted in the identification of REP27, a nuclear gene encoding a putative chloroplast-targeted protein, which is specifically required for the completion of the D1 turnover process but is not essential for the de novo biogenesis and assembly of the PSII holocomplex in this model green alga. The REP27 protein contains two highly conserved tetratricopeptide repeats, postulated to facilitate the psbA mRNA cotranslational insertion of the nascent D1 protein in the existing PSII core template. Elucidation of the PSII repair mechanism may reveal the occurrence of hitherto unknown regulatory and catalytic reactions for the selective in situ replacement of specific proteins from within multiprotein complexes.

Place, publisher, year, edition, pages
American Society of Plant Biologists , 2007. Vol. 143, 1547-60 p.
URN: urn:nbn:se:umu:diva-21016DOI: 10.1104/pp.107.096396OAI: diva2:210329
OPEN ACCESS ARTICLEAvailable from: 2009-04-01 Created: 2009-04-01 Last updated: 2009-09-15Bibliographically approved
In thesis
1. Functions of REP27 and the low molecular weight proteins PsbX and PsbW in repair and assembly of photosystem II
Open this publication in new window or tab >>Functions of REP27 and the low molecular weight proteins PsbX and PsbW in repair and assembly of photosystem II
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]



Oxygenic photosynthesis is the major producer of both oxygen and organic compounds on earth and takes place in plants, green algae and cyanobacteria. The thylakoid membranes are the site of the photosynthetic light reactions that involve the concerted action of four major protein complexes known as photosystem II (PSII), cytochrome b6f complex, ATP synthase and photosystem I (PSI). The function of PSII is of particular interest as it performs the light–driven water splitting reaction driving the photosynthetic electron transport. My thesis addressed different aspects of PSII assembly and the functions of its low molecular weight PSII subunits PsbX and PsbW. Photosynthesis in green algae and higher plants is controlled by the nucleus. Many proteins of nuclear origin participate in the regulation of the efficient assembly of the photosynthetic protein complexes. In this investigation we have identified one of these nuclear encoded auxiliary proteins of photosystem II, REP27, which participates in the assembly of the D1 reaction center protein and repair of photodamaged PSII in the green algae Chlamydomonas reinhardtii. Interestingly, PSII is specially enriched in Low Molecular Weight (LMW) subunits that have masses less than 10kDa. These proteins account for more than the half of the PSII subunits. Several questions remains poorly understood regarding the LMW: Which is their evolutionary origin? What function do they perform in the protein complex? Where are they located in the protein structure? In this investigation the functions of two of these LMW subunits (PsbX and PsbW) have been studied using antisense inhibition and T-DNA knockout mutant plants in Arabidopsis thaliana. Deficiency of the PsbX protein leads to impaired accumulation and functionality of PSII. Characterization of PsbW knock-out plants show that PsbW participates in stabilization of the macro-organization of PSII and the peripheral antenna (Light Harvesting Complex, LHCII) in the grana stacks of the chloroplast, also known as PSII-LHCII supercomplexes.



50 p.
Photosynthesis, photosystem II reaction center, PSII-LHCII supercomplex, antisense plant, T-DNA knockout plant, auxiliary protein
Research subject
urn:nbn:se:umu:diva-19517 (URN)978-91-7264-752-7 (ISBN)
Public defence
2009-03-27, KB3B1, KBC, Umeå, 10:00 (English)
Available from: 2009-03-10 Created: 2009-03-05 Last updated: 2009-09-15Bibliographically approved

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