Biochemical and structural analyses of a higher plant photosystem II supercomplex of a photosystem I‐less mutant of barley

University of Verona, Verona, Veneto, Italy
FEBS Journal (Impact Factor: 4). 11/2006; 273(20):4616-30. DOI: 10.1111/j.1742-4658.2006.05465.x
Source: PubMed


Photosystem II of higher plants is a multisubunit transmembrane complex composed of a core moiety and an extensive peripheral antenna system. The number of antenna polypeptides per core complex is modulated following environmental conditions in order to optimize photosynthetic performance. In this study, we used a barley (Hordeum vulgare) mutant, viridis zb63, which lacks photosystem I, to mimic extreme and chronic overexcitation of photosystem II. The mutation was shown to reduce the photosystem II antenna to a minimal size of about 100 chlorophylls per photosystem II reaction centre, which was not further reducible. The minimal photosystem II unit was analysed by biochemical methods and by electron microscopy, and found to consist of a dimeric photosystem II reaction centre core surrounded by monomeric Lhcb4 (chlorophyll protein 29), Lhcb5 (chlorophyll protein 26) and trimeric light-harvesting complex II antenna proteins. This minimal photosystem II unit forms arrays in vivo, possibly to increase the efficiency of energy distribution and provide photoprotection. In wild-type plants, an additional antenna protein, chlorophyll protein 24 (Lhcb6), which is not expressed in viridis zb63, is proposed to associate to this minimal unit and stabilize larger antenna systems when needed. The analysis of the mutant also revealed the presence of two distinct signalling pathways activated by excess light absorbed by photosystem II: one, dependent on the redox state of the electron transport chain, is involved in the regulation of antenna size, and the second, more directly linked to the level of photoinhibitory stress perceived by the cell, participates in regulating carotenoid biosynthesis.

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Available from: Tomas Morosinotto
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    • "Densitometric analysis of the electrophoretic profile showed that the different light treatments differently affected the PSII antenna/PSII core-complex ratio. A significant decrease in the PSII antenna/ PSII core-complex ratio was observed after acclimation to HL (from 7.0 in LL to 5.2 in HL), which is in agreement with data obtained previously (Morosinotto et al., 2006; Kouřil et al., 2013). The HL treatment of leaves in the presence of exogenous catalase did not lead to the same decrease in the PSII antenna/PSII core ratio, only reaching 6.3, which was Fig. 2 "
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    ABSTRACT: Higher plants possess the ability to trigger a long-term acclimatory response to different environmental light conditions through the regulation of the light-harvesting antenna size of photosystem II. The present study provides an insight into the molecular nature of the signal which initiates the high light-mediated response of a reduction in antenna size. Using barley (Hordeum vulgare) plants, it is shown (i) that the light-harvesting antenna size is not reduced in high light with a low hydrogen peroxide content in the leaves; and (ii) that a decrease in the antenna size is observed in low light in the presence of an elevated concentration of hydrogen peroxide in the leaves. In particular, it has been demonstrated that the ability to reduce the antenna size of photosystem II in high light is restricted to photosynthetic apparatus with a reduced level of the plastoquinone pool and with a low hydrogen peroxide content. Conversely, the reduction of antenna size in low light is induced in photosynthetic apparatus possessing elevated hydrogen peroxide even when the reduction level of the plastoquinone pool is low. Hydrogen peroxide affects the relative abundance of the antenna proteins that modulate the antenna size of photosystem II through a down-regulation of the corresponding lhcb mRNA levels. This work shows that hydrogen peroxide contributes to triggering the photosynthetic apparatus response for the reduction of the antenna size of photosystem II by being the molecular signal for the long-term acclimation of plants to high light. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email:
    Full-text · Article · Aug 2015 · Journal of Experimental Botany
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    • "In our native gels using a much softer and partial solubilization of thylakoid with digitonin (see Supplemental Figure 1A online), we did not detect a difference in PSII supercomplex distribution between State I and II membranes. Thus, by considering our results (Figures 4A and 5), the possibility of differently interpreting previous reports (Dietzel et al., 2011; García-Cerdán et al., 2011), the fact that trimer S has a fundamental role in PSII structure (Dekker and Boekema, 2005; Caffarri et al., 2009), and that the minimum PSII antenna size includes S-LHCII (Morosinotto et al., 2006), we consider that S trimer detachment from PSII during state transition is rather unlikely and could have, at best, a limited impact on the whole process under physiological conditions. Even if we cannot exclude that a functional PSI-LHCII-PSII interaction exists in vivo, from our results, such a megacomplex would be maintained by very weak interactions (those between PSII and L trimers) that do not resist our very mild solubilization (see Supplemental Figure 1A online). "
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    ABSTRACT: State transitions are an important photosynthetic short-term response that allows energy distribution balancing between photosystems I (PSI) and II (PSII). In plants when PSII is preferentially excited compared with PSI (State II), part of the major light-harvesting complex LHCII migrates to PSI to form a PSI-LHCII supercomplex. So far, little is known about this complex, mainly due to purification problems. Here, a stable PSI-LHCII supercomplex is purified from Arabidopsis thaliana and maize (Zea mays) plants. It is demonstrated that LHCIIs loosely bound to PSII in State I are the trimers mainly involved in state transitions and become strongly bound to PSI in State II. Specific Lhcb1-3 isoforms are differently represented in the mobile LHCII compared with S and M trimers. Fluorescence analyses indicate that excitation energy migration from mobile LHCII to PSI is rapid and efficient, and the quantum yield of photochemical conversion of PSI-LHCII is substantially unaffected with respect to PSI, despite a sizable increase of the antenna size. An updated PSI-LHCII structural model suggests that the low-energy chlorophylls 611 and 612 in LHCII interact with the chlorophyll 11145 at the interface of PSI. In contrast with the common opinion, we suggest that the mobile pool of LHCII may be considered an intimate part of the PSI antenna system that is displaced to PSII in State I.
    Full-text · Article · Jul 2012 · The Plant Cell
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    • "n a 1 : 1 ratio ( B4 ; Caffarri et al . , 2009 ) was analyzed in the same gel system . A 1 . 1 times stronger binding to CP29 than to LHCII was found . CP29 is assumed to be present at stoichiometric amounts with the PSII core , based on its presence in the smallest C 2 S 2 ( dimeric core with two strongly bound LHCII trimers ) PSII supercomplex ( Morosinotto et al . , 2006 ; Caffarri et al . , 2009 ) . To our knowledge , no substantial amount of PSII core without associated Lhcb antenna can be present in wild - type plants . Eight repetitions from three different leaves per growth light treatment were used . The PSI : PSII ratio was calculated from the measured chlorophyll a : b ratio as described by Croc"
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    ABSTRACT: The mechanisms underlying the wavelength dependence of the quantum yield for CO(2) fixation (α) and its acclimation to the growth-light spectrum are quantitatively addressed, combining in vivo physiological and in vitro molecular methods. Cucumber (Cucumis sativus) was grown under an artificial sunlight spectrum, shade light spectrum, and blue light, and the quantum yield for photosystem I (PSI) and photosystem II (PSII) electron transport and α were simultaneously measured in vivo at 20 different wavelengths. The wavelength dependence of the photosystem excitation balance was calculated from both these in vivo data and in vitro from the photosystem composition and spectroscopic properties. Measuring wavelengths overexciting PSI produced a higher α for leaves grown under the shade light spectrum (i.e., PSI light), whereas wavelengths overexciting PSII produced a higher α for the sun and blue leaves. The shade spectrum produced the lowest PSI:PSII ratio. The photosystem excitation balance calculated from both in vivo and in vitro data was substantially similar and was shown to determine α at those wavelengths where absorption by carotenoids and nonphotosynthetic pigments is insignificant (i.e., >580 nm). We show quantitatively that leaves acclimate their photosystem composition to their growth light spectrum and how this changes the wavelength dependence of the photosystem excitation balance and quantum yield for CO(2) fixation. This also proves that combining different wavelengths can enhance quantum yields substantially.
    Full-text · Article · May 2012 · The Plant Cell
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