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Accessibility controls selective degradation of photosystem II subunits by FtsH protease


The oxygen-evolving photosystem II (PSII) complex located in chloroplasts and cyanobacteria is sensitive to light-induced damage1 that unless repaired causes reduction in photosynthetic capacity and growth. Although a potential target for crop improvement, the mechanism of PSII repair remains unclear. The D1 reaction center protein is the main target for photodamage2, with repair involving the selective degradation of the damaged protein by FtsH protease3. How a single damaged PSII subunit is recognized for replacement is unknown. Here, we have tested the dark stability of PSII subunits in strains of the cyanobacterium Synechocystis PCC 6803 blocked at specific stages of assembly. We have found that when D1, which is normally shielded by the CP43 subunit, becomes exposed in a photochemically active PSII complex lacking CP43, it is selectively degraded by FtsH even in the dark. Removal of the CP47 subunit, which increases accessibility of FtsH to the D2 subunit, induced dark degradation of D2 at a faster rate than that of D1. In contrast, CP47 and CP43 are resistant to degradation in the dark. Our results indicate that protease accessibility induced by PSII disassembly is an important determinant in the selection of the D1 and D2 subunits to be degraded by FtsH.

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Figure 1: Structure and dark stability of wild-type and mutant PSII.
Figure 2: Structure of RC47 and dark stability of ΔCP43 mutants.
Figure 3: Structure of RCII and dark stability of ΔCP47 mutants.
Figure 4: Model of the selective degradation of the D1 and D2 proteins.


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V.K. and J.K. were supported by the National Programme of Sustainability I, ID: LO1416 and by the project P501/12/G055 of the Grant Agency of the Czech Republic, S.S. and P.J.N. by the BBSRC (grant BB/L003260/1) and S.S. by China Scholarship Council.

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V.K. performed experiments and protein analyses under the supervision of J.K., J.K. designed the study, S.S. made model figures and P.J.N. and J.K. wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Josef Komenda.

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The authors declare no competing financial interests.

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Krynická, V., Shao, S., Nixon, P. et al. Accessibility controls selective degradation of photosystem II subunits by FtsH protease. Nature Plants 1, 15168 (2015).

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