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      Functional analysis of LHCSR1, a protein catalyzing NPQ in mosses, by heterologous expression in Arabidopsis thaliana

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          Abstract

          Non-photochemical quenching, NPQ, of chlorophyll fluorescence regulates the heat dissipation of chlorophyll excited states and determines the efficiency of the oxygenic photosynthetic systems. NPQ is regulated by a pH-sensing protein, responding to the chloroplast lumen acidification induced by excess light, coupled to an actuator, a chlorophyll/xanthophyll subunit where quenching reactions are catalyzed. In plants, the sensor is PSBS, while the two pigment-binding proteins Lhcb4 (also known as CP29) and LHCII are the actuators. In algae and mosses, stress-related light-harvesting proteins (LHCSR) comprise both functions of sensor and actuator within a single subunit. Here, we report on expressing the lhcsr1 gene from the moss Physcomitrella patens into several Arabidopsis thaliana npq4 mutants lacking the pH sensing PSBS protein essential for NPQ activity. The heterologous protein LHCSR1 accumulates in thylakoids of A. thaliana and NPQ activity can be partially restored. Complementation of double mutants lacking, besides PSBS, specific xanthophylls, allowed analyzing chromophore requirement for LHCSR-dependent quenching activity. We show that the partial recovery of NPQ is mostly due to the lower levels of Zeaxanthin in A. thaliana in comparison to P. patens. Complemented npq2npq4 mutants, lacking besides PSBS, Zeaxanthin Epoxidase, showed an NPQ recovery of up to 70% in comparison to A. thaliana wild type. Furthermore, we show that Lutein is not essential for the folding nor for the quenching activity of LHCSR1. In short, we have developed a system to study the function of LHCSR proteins using heterologous expression in a variety of A. thaliana mutants.

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          Most cited references42

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          A pigment-binding protein essential for regulation of photosynthetic light harvesting.

          Photosynthetic light harvesting in plants is regulated in response to changes in incident light intensity. Absorption of light that exceeds a plant's capacity for fixation of CO2 results in thermal dissipation of excitation energy in the pigment antenna of photosystem II by a poorly understood mechanism. This regulatory process, termed nonphotochemical quenching, maintains the balance between dissipation and utilization of light energy to minimize generation of oxidizing molecules, thereby protecting the plant against photo-oxidative damage. To identify specific proteins that are involved in nonphotochemical quenching, we have isolated mutants of Arabidopsis thaliana that cannot dissipate excess absorbed light energy. Here we show that the gene encoding PsbS, an intrinsic chlorophyll-binding protein of photosystem II, is necessary for nonphotochemical quenching but not for efficient light harvesting and photosynthesis. These results indicate that PsbS may be the site for nonphotochemical quenching, a finding that has implications for the functional evolution of pigment-binding proteins.
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            REGULATION OF LIGHT HARVESTING IN GREEN PLANTS.

            When plants are exposed to light intensities in excess of those that can be utilized in photosynthetic electron transport, nonphotochemical dissipation of excitation energy is induced as a mechanism for photoprotection of photosystem II. The features of this process are reviewed, particularly with respect to the molecular mechanisms involved. It is shown how the dynamic properties of the proteins and pigments of the chlorophyll a/b light-harvesting complexes of photosystem II first enable the level of excitation energy to be sensed via the thylakoid proton gradient and subsequently allow excess energy to be dissipated as heat by formation of a nonphotochemical quencher. The nature of this quencher is discussed, together with a consideration of how the variation in capacity for energy dissipation depends on specific features of the composition of the light-harvesting system. Finally, the prospects for future progress in understanding the regulation of light harvesting are assessed.
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              Arabidopsis mutants define a central role for the xanthophyll cycle in the regulation of photosynthetic energy conversion.

              A conserved regulatory mechanism protects plants against the potentially damaging effects of excessive light. Nearly all photosynthetic eukaryotes are able to dissipate excess absorbed light energy in a process that involves xanthophyll pigments. To dissect the role of xanthophylls in photoprotective energy dissipation in vivo, we isolated Arabidopsis xanthophyll cycle mutants by screening for altered nonphotochemical quenching of chlorophyll fluorescence. The npq1 mutants are unable to convert violaxanthin to zeaxanthin in excessive light, whereas the npq2 mutants accumulate zeaxanthin constitutively. The npq2 mutants are new alleles of aba1, the zeaxanthin epoxidase gene. The high levels of zeaxanthin in npq2 affected the kinetics of induction and relaxation but not the extent of nonphotochemical quenching. Genetic mapping, DNA sequencing, and complementation of npq1 demonstrated that this mutation affects the structural gene encoding violaxanthin deepoxidase. The npq1 mutant exhibited greatly reduced nonphotochemical quenching, demonstrating that violaxanthin deepoxidation is required for the bulk of rapidly reversible nonphotochemical quenching in Arabidopsis. Altered regulation of photosynthetic energy conversion in npq1 was associated with increased sensitivity to photoinhibition. These results, in conjunction with the analysis of npq mutants of Chlamydomonas, suggest that the role of the xanthophyll cycle in nonphotochemical quenching has been conserved, although different photosynthetic eukaryotes rely on the xanthophyll cycle to different extents for the dissipation of excess absorbed light energy.
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                Author and article information

                Contributors
                ioannisdikaios@hotmail.com
                christo.schiphorst@univr.it
                luca.dallosto@univr.it
                alessandro.alboresi@unipd.it
                roberto.bassi@univr.it
                +39 (0)382 985524 , alberta.pinnola@unipv.it
                Journal
                Photosynth Res
                Photosyn. Res
                Photosynthesis Research
                Springer Netherlands (Dordrecht )
                0166-8595
                1573-5079
                3 July 2019
                3 July 2019
                2019
                : 142
                : 3
                : 249-264
                Affiliations
                [1 ]GRID grid.5611.3, ISNI 0000 0004 1763 1124, Department of Biotechnology, , University of Verona, ; Verona, 37134 Italy
                [2 ]GRID grid.8982.b, ISNI 0000 0004 1762 5736, Department of Biology and Biotechnology, , University of Pavia, ; Pavia, 27100 Italy
                Author information
                http://orcid.org/0000-0003-3333-5264
                http://orcid.org/0000-0001-9497-5156
                http://orcid.org/0000-0003-4818-7778
                http://orcid.org/0000-0002-4140-8446
                http://orcid.org/0000-0001-8373-7638
                Article
                656
                10.1007/s11120-019-00656-3
                6874524
                31270669
                9aca9957-a489-441b-9a12-8b91ce5b4c3c
                © The Author(s) 2019

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

                History
                : 11 February 2019
                : 27 June 2019
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/100010665, H2020 Marie Skłodowska-Curie Actions;
                Award ID: 675006-SE2B
                Award ID: 316427-ACCLIPHOT
                Award Recipient :
                Categories
                Original Article
                Custom metadata
                © Springer Nature B.V. 2019

                Plant science & Botany
                lhcsr,npq,photoprotection,heterologous expression,p. patens,a. thaliana
                Plant science & Botany
                lhcsr, npq, photoprotection, heterologous expression, p. patens, a. thaliana

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