Physiological links among alternative electron transport pathways that reduce and oxidize plastoquinone in Arabidopsis

Okegawa, Yuki; Kobayashi, Yoshitaka; Shikanai, Toshiharu

doi:10.1111/j.1365-313x.2010.04252.x

Cited by 77 publications

(70 citation statements)

References 50 publications

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“…PSI level is reduced in crr4-2 pgr5 (Fig. 4, D and E) and crr2 pgr5 (Okegawa et al, 2010), probably due to the photoinhibition of PSI. A similar phenotype was found in lhca5 lhca6 pgr5 (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…In contrast to D1 and Cyt f, which were not affected in these plants, the PSI subunit PsaA was reduced to various extents in the mature leaves of lhca6 pgr5 and lhca5 lhca6 pgr5 plants as well as in crr4-2 pgr5 plants. The decrease in PSI levels in these plants would result from PSI photodamage (Munekage et al, 2004;Okegawa et al, 2010).…”

Section: Mutant Backgroundmentioning

confidence: 99%

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Supercomplex Formation with Photosystem I Is Required for the Stabilization of the Chloroplast NADH Dehydrogenase-Like Complex in Arabidopsis

Peng

Shikanai

2011

Plant Physiology

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In higher plants, the chloroplast NADH dehydrogenase-like complex (NDH) interacts with photosystem I (PSI) to form the NDH-PSI supercomplex via two minor light-harvesting complex I (LHCI) proteins, Lhca5 and Lhca6. Previously, we showed that in lhca5 and lhca6, NDH still associates with PSI to form smaller versions of the NDH-PSI supercomplex, although their molecular masses are far smaller than that of the full-size NDH-PSI supercomplex. In this study, we show that the NDH complex is present in the monomeric form in Arabidopsis (Arabidopsis thaliana) lhca5 lhca6, implying that NDH interacts with multiple copies of PSI. NDH subunit levels were slightly reduced in immature leaves and more drastically (approximately 50%) in mature leaves of the lhca5 lhca6 double mutant compared with the wild type. Chlorophyll fluorescence analyses detected NDH activity of lhca5 lhca6, suggesting that the supercomplex formation is not essential for NDH activity. However, the severe phenotypes of the lhca5 lhca6 proton gradient regulation5 triple mutant in both plant growth rate and photosynthesis suggest that the function of NDH was impaired in this mutant in vivo. Accumulation of NDH subunits was drastically reduced in lhca5 lhca6 when the light intensity was shifted from 50 to 500 mmol photons m 22 s 21 . Furthermore, the half-life of NDH subunits, especially that of NDH18, was shorter in monomeric NDH than in the NDH-PSI supercomplex under the high-light conditions. We propose that NDH-PSI supercomplex formation stabilizes NDH and that the process is especially required under stress conditions.

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Section: Discussionmentioning

confidence: 99%

Section: Mutant Backgroundmentioning

confidence: 99%

Supercomplex Formation with Photosystem I Is Required for the Stabilization of the Chloroplast NADH Dehydrogenase-Like Complex in Arabidopsis

Peng

Shikanai

2011

Plant Physiology

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“…In plants, such a slow oxidation is sufficient to keep the pool oxidized, so that it must be paralleled by an even slower reduction rate. Simply overexpressing PTOX does not provide the expected benefits in Arabidopsis (25) or tobacco (26), whereas the leaf variegation phenotype of im is alleviated at low light intensities by inactivation of NDH and PGR5 (27). Alpine species not only accumulate higher levels of PTOX but also detoxification enzymes (10,11) and NDH (28).…”

Section: Discussionmentioning

confidence: 99%

Plastid terminal oxidase 2 (PTOX2) is the major oxidase involved in chlororespiration in Chlamydomonas

Houille-Vernes

Rappaport

Wollman

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

163

156

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By homology with the unique plastid terminal oxidase (PTOX) found in plants, two genes encoding oxidases have been found in the Chlamydomonas genome, PTOX1 and PTOX2. Here we report the identification of a knockout mutant of PTOX2. Its molecular and functional characterization demonstrates that it encodes the oxidase most predominantly involved in chlororespiration in this algal species. In this mutant, the plastoquinone pool is constitutively reduced under dark-aerobic conditions, resulting in the mobile lightharvesting complexes being mainly, but reversibly, associated with photosystem I. Accordingly, the ptox2 mutant shows lower fitness than wild type when grown under phototrophic conditions. Single and double mutants devoid of the cytochrome b 6 f complex and PTOX2 were used to measure the oxidation rates of plastoquinols via PTOX1 and PTOX2. Those lacking both the cytochrome b 6 f complex and PTOX2 were more sensitive to light than the single mutants lacking either the cytochrome b 6 f complex or PTOX2, which discloses the role of PTOX2 under extreme conditions where the plastoquinone pool is overreduced. A model for chlororespiration is proposed to relate the electron flow rate through these alternative pathways and the redox state of plastoquinones in the dark. This model suggests that, in green algae and plants, the redox poise results from the balanced accumulation of PTOX and NADPH dehydrogenase.Chlamydomonas reinhardtii | state transitions | chloroplast | photosynthesis

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“…The P 700 oxidation ratio was measured as described by Okegawa et al (2010) and was calculated as DA/DA max , where DA max is the maximal P 700 + level induced by a 50-ms pulse of intense white light under FR light illumination and DA is the steady-state P 700 + level during illumination with white light (photon flux density of 100 or 1,000 mmol m 22 s 21 ).…”

Section: Redox State Of P 700mentioning

confidence: 99%

Thioredoxin m4 Controls Photosynthetic Alternative Electron Pathways in Arabidopsis

et al. 2012

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In addition to the linear electron flow, a cyclic electron flow (CEF) around photosystem I occurs in chloroplasts. In CEF, electrons flow back from the donor site of photosystem I to the plastoquinone pool via two main routes: one that involves the Proton Gradient Regulation5 (PGR5)/PGRL1 complex (PGR) and one that is dependent of the NADH dehydrogenase-like complex. While the importance of CEF in photosynthesis and photoprotection has been clearly established, little is known about its regulation. We worked on the assumption of a redox regulation and surveyed the putative role of chloroplastic thioredoxins (TRX). Using Arabidopsis (Arabidopsis thaliana) mutants lacking different TRX isoforms, we demonstrated in vivo that TRXm4 specifically plays a role in the down-regulation of the NADH dehydrogenase-like complex-dependent plastoquinone reduction pathway. This result was confirmed in tobacco (Nicotiana tabacum) plants overexpressing the TRXm4 orthologous gene. In vitro assays performed with isolated chloroplasts and purified TRXm4 indicated that TRXm4 negatively controls the PGR pathway as well. The physiological significance of this regulation was investigated under steady-state photosynthesis and in the pgr5 mutant background. Lack of TRXm4 reversed the growth phenotype of the pgr5 mutant, but it did not compensate for the impaired photosynthesis and photoinhibition sensitivity. This suggests that the physiological role of TRXm4 occurs in vivo via a mechanism distinct from direct up-regulation of CEF.

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Physiological links among alternative electron transport pathways that reduce and oxidize plastoquinone in Arabidopsis

Cited by 77 publications

References 50 publications

Supercomplex Formation with Photosystem I Is Required for the Stabilization of the Chloroplast NADH Dehydrogenase-Like Complex in Arabidopsis

Supercomplex Formation with Photosystem I Is Required for the Stabilization of the Chloroplast NADH Dehydrogenase-Like Complex in Arabidopsis

Plastid terminal oxidase 2 (PTOX2) is the major oxidase involved in chlororespiration in Chlamydomonas

Thioredoxin m4 Controls Photosynthetic Alternative Electron Pathways in Arabidopsis

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