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A redox-active FKBP-type immunophilin functions in accumulation of the photosystem II supercomplex in Arabidopsis thaliana.

ABSTRACT: Photosystem II (PSII) catalyzes the first of two photosynthetic reactions that convert sunlight into chemical energy. Native PSII is a supercomplex consisting of core and light-harvesting chlorophyll proteins. Although the structure of PSII has been resolved by x-ray crystallography, the mechanism underlying its assembly is poorly understood. Here, we report that an immunophilin of the chloroplast thylakoid lumen is required for accumulation of the PSII supercomplex in Arabidopsis thaliana. The immunophilin, FKBP20-2, belongs to the FK-506 binding protein (FKBP) subfamily that functions as peptidyl-prolyl isomerases (PPIases) in protein folding. FKBP20-2 has a unique pair of cysteines at the C terminus and was found to be reduced by thioredoxin (Trx) (itself reduced by NADPH by means of NADP-Trx reductase). The FKBP20-2 protein, which contains only two of the five amino acids required for catalysis, showed a low level of PPIase activity that was unaffected on reduction by Trx. Genetic disruption of the FKBP20-2 gene resulted in reduced plant growth, consistent with the observed lower rate of PSII activity determined by fluorescence (using leaves) and oxygen evolution (using isolated chloroplasts). Analysis of isolated thylakoid membranes with blue native gels and immunoblots showed that accumulation of the PSII supercomplex was compromised in mutant plants, whereas the levels of monomer and dimer building blocks were elevated compared with WT. The results provide evidence that FKBP20-2 participates specifically in the accumulation of the PSII supercomplex in the chloroplast thylakoid lumen by means of a mechanism that has yet to be determined.

SUBMITTER: Lima A

PROVIDER: S-EPMC1567930 | biostudies-literature | 2006 Aug

REPOSITORIES: biostudies-literature

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A redox-active FKBP-type immunophilin functions in accumulation of the photosystem II supercomplex in Arabidopsis thaliana.

Lima Amparo A Lima Santiago S Wong Joshua H JH Phillips Robert S RS Buchanan Bob B BB Luan Sheng S

Proceedings of the National Academy of Sciences of the United States of America 20060807 33

Photosystem II (PSII) catalyzes the first of two photosynthetic reactions that convert sunlight into chemical energy. Native PSII is a supercomplex consisting of core and light-harvesting chlorophyll proteins. Although the structure of PSII has been resolved by x-ray crystallography, the mechanism underlying its assembly is poorly understood. Here, we report that an immunophilin of the chloroplast thylakoid lumen is required for accumulation of the PSII supercomplex in Arabidopsis thaliana. The ...[more]

PMID: 16894144

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Project description:Columbia-0 (Col-0), Wassilewskija-4 (Ws-4), and Landsberg erecta-0 (Ler-0) are used as background lines for many public Arabidopsis mutant collections, and for investigation in laboratory conditions of plant processes, including photosynthesis and response to high-intensity light (HL). The photosystem II (PSII) complex is sensitive to HL and requires repair to sustain its function. PSII repair is a multistep process controlled by numerous factors, including protein phosphorylation and thylakoid membrane stacking. Here we have characterized the function and dynamics of PSII complex under growth-light and HL conditions. Ws-4 displayed 30% more thylakoid lipids per chlorophyll and 40% less chlorophyll per carotenoid than Col-0 and Ler-0. There were no large differences in thylakoid stacking, photoprotection and relative levels of photosynthetic complexes among the three accessions. An increased efficiency of PSII closure was found in Ws-4 following illumination with saturation flashes or continuous light. Phosphorylation of the PSII D1/D2 proteins was reduced by 50% in Ws-4 as compared to Col-0 and Ler-0. An increase in abundance of the responsible STN8 kinase in response to HL treatment was found in all three accessions, but Ws-4 displayed 50% lower levels than Col-0 and Ler-0. Despite this, the HL treatment caused in Ws-4 the lagest extent of PSII inactivation, disassembly, D1 protein degradation, and the largest decrease in the size of stacked thylakoids. The dilution of chlorophyll-protein complexes with additional lipids and carotenoids in Ws-4 may represent a mechanism to facilitate lateral protein traffic in the membrane, thus compensating for the lack of a full complement of STN8 kinase. Nevertheless, additional PSII damage occurs in Ws-4, which exceeds the D1 protein synthesis capacity, thus leading to enhanced photoinhibition. Our findings are valuable for selection of appropriate background line for PSII characterization in Arabidopsis mutants, and also provide the first insights into natural variation of PSII protein phosphorylation.

Dataset Information

A redox-active FKBP-type immunophilin functions in accumulation of the photosystem II supercomplex in Arabidopsis thaliana.

Publications

A redox-active FKBP-type immunophilin functions in accumulation of the photosystem II supercomplex in Arabidopsis thaliana.

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