Proton gradient regulation 5 (PGR5) is involved in the control of photosynthetic electron transfer, but its mechanistic role is not yet clear. Several models have been proposed to explain phenotypes such as a diminished steady-state proton motive force (pmf) and increased photodamage of photosystem I (PSI). Playing a regulatory role in cyclic electron flow (CEF) around PSI, PGR5 contributes indirectly to PSI protection by enhancing photosynthetic control, which is a pH-dependent down-regulation of electron transfer at the cytochrome b6f complex (b6f). Here, we re-evaluated the role of PGR5 in the green alga Chlamydomonas reinhardtii and conclude that pgr5 possesses a dysfunctional b6f. Our data indicate that the b6f low-potential chain redox activity likely operated in two distinct modes — via the canonical Q cycle during linear electron flow and via an alternative Q cycle during CEF, which allowed efficient oxidation of the low-potential chain in the WT b6f. A switch between the two Q cycle modes was dependent on PGR5 and relied on unknown stromal electron carrier(s), which were a general requirement for b6f activity. In CEF-favoring conditions, the electron transfer bottleneck in pgr5 was the b6f, in which insufficient low-potential chain redox tuning might account for the mutant pmf phenotype. By attributing a ferredoxin-plastoquinone reductase activity to the b6f and investigating a PGR5 cysteine mutant, a current model of CEF is challenged.
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May 2020
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Cover Image
Hot and cold spots in N-TIMP2 interacting with MMP-1 (green), MMP-3 (purple) and MMP-14 (blue). Each couple present 180° rotation with respect to each other. Hot spots (red) and cold spots (blue) are shown on the interface of N-TIMP2. To learn more about this, see the article by Aharon and colleagues (pp. 1701–1719) in this issue. The image was provided by Niv Papo.
Research Article|
May 05 2020
PGR5 is required for efficient Q cycle in the cytochrome b6f complex during cyclic electron flow
Felix Buchert
;
Felix Buchert
1Institute of Plant Biology and Biotechnology, University of Münster, Schlossplatz 8, 48143 Münster, Germany
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Laura Mosebach;
Laura Mosebach
1Institute of Plant Biology and Biotechnology, University of Münster, Schlossplatz 8, 48143 Münster, Germany
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Philipp Gäbelein;
Philipp Gäbelein
1Institute of Plant Biology and Biotechnology, University of Münster, Schlossplatz 8, 48143 Münster, Germany
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Michael Hippler
1Institute of Plant Biology and Biotechnology, University of Münster, Schlossplatz 8, 48143 Münster, Germany
2Institute of Plant Science and Resources, Okayama University, Kurashiki, Japan
Correspondence: Michael Hippler (mhippler@uni-muenster.de)
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Publisher: Portland Press Ltd
Received:
December 10 2019
Revision Received:
March 23 2020
Accepted:
April 07 2020
Accepted Manuscript online:
April 08 2020
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 2020 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society
2020
Biochem J (2020) 477 (9): 1631–1650.
Article history
Received:
December 10 2019
Revision Received:
March 23 2020
Accepted:
April 07 2020
Accepted Manuscript online:
April 08 2020
Citation
Felix Buchert, Laura Mosebach, Philipp Gäbelein, Michael Hippler; PGR5 is required for efficient Q cycle in the cytochrome b6f complex during cyclic electron flow. Biochem J 15 May 2020; 477 (9): 1631–1650. doi: https://doi.org/10.1042/BCJ20190914
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