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SUMMARY: Photosystem II (PSII) complexes are organized into large supercomplexes with variable amounts of light‐harvesting proteins (Lhcb). A typical PSII supercomplex in plants is formed by four trimers of Lhcb proteins (LHCII trimers), which are bound to the PSII core dimer via monomeric antenna proteins. However, the architecture of PSII supercomplexes in Norway spruce[Picea abies (L.) Karst.] is different, most likely due to a lack of two Lhcb proteins, Lhcb6 and Lhcb3. Interestingly, the spruce PSII supercomplex shares similar structural features with its counterpart in the green alga Chlamydomonas reinhardtii [Kouřil et al. (2016) New Phytol. 210, 808–814]. Here we present a single‐particle electron microscopy study of isolated PSII supercomplexes from Norway spruce that revealed binding of a variable amount of LHCII trimers to the PSII core dimer at positions that have never been observed in any other plant species so far. The largest spruce PSII supercomplex, which was found to bind eight LHCII trimers, is even larger than the current largest known PSII supercomplex from C. reinhardtii. We have also shown that the spruce PSII supercomplexes can form various types of PSII megacomplexes, which were also identified in intact grana membranes. Some of these large PSII supercomplexes and megacomplexes were identified also in Pinus sylvestris, another representative of the Pinaceae family. The structural variability and complexity of LHCII organization in Pinaceae seems to be related to the absence of Lhcb6 and Lhcb3 in this family, and may be beneficial for the optimization of light‐harvesting under varying environmental conditions. Significance Statement: Norway spruce is known to lack two Lhcb proteins (Lhcb6 and Lhcb3), and its photosystems II (PSII) are organized into supercomplexes, which are similar to those observed in the green alga Chlamydomonas reinhardtii. Here we show that PSII in spruce can bind even more light‐harvesting complexes than PSII in Chlamydomonas, which makes it the largest PSII supercomplex ever observed, and that spruce supercomplexes can form various megacomplexes, detectable also in intact grana membranes. [ABSTRACT FROM AUTHOR]

The essay of Lukas Nosek, an arabist and a catholic theologian, deals with Pierre Claverie's relation with the truth. It is based on Claverie's position in the study called Humanite plurielle, which states that Christians are not owners of the truth but rather vice-versa, the truth "owns" Christians. The author asks a question whether this approach isn't overly relativistic, whether Claverie abandoned catholic or even Christian faith. If argumentative skills and syllogisms are not enough and a need of other person is declared, what kind of concept of the truth is it? Therefore, Nosek explores how Christian and Muslim authorities approach the truth. At first he examines On First Philosophy, the work of al-Kindi, a founder of Islamic and Arabic philosophy. Then he analyzes a passage about grace in Summa Theologica by St. Thomas Aquinas, the letter De modo studendi accredited to St. Thomas for a long time and finally the work of a medieval reformer Jan Hus. Nosek uncovers that all the above mentioned thinkers have been defending the autonomy of the truth, the impossibility of its possession but also the chance to approach it. The essential point is the necessity to admit that truth can be revealed through somebody different (a foreigner, a member of other religious group, a heretic). We need others to be able to see things from different angles and to observe mysterious unity of the Truth of being from various perspectives and in particular traditions as it has been declared by fathers of the Second Vatican Council after all. [ABSTRACT FROM AUTHOR]

The article presents a practical guidance for catechists, preachers and pastoral workers and for their possible contact with Muslims in the Czech republic. This article presents a strong and joyful faith in the Christ in one hand and a desire of understanding between religions as a needed preconditions for the Interreligious Dialogue. The preacher has to be acquainted with the deep knowledge of Islam, its culture and the local muslim community. Also his rhetorical skills and a strong personality are strongly required. Further it shows the inspiration of proclamation of Christ which is based on similarities of the Bible and the Koran, and of the articles of faith and of the piety. At the end it is highly important to mention the knowledge of the classical Arabic literature and to search for elements of truth in it. [ABSTRACT FROM AUTHOR]

The study summarises the objections of some critical voices against the post-synodal exhortation Amoris Laetitia, especially against its 8th chapter. It is neither a complete list of critical voices nor a complete list of their arguments; it is limited to the two loudest and apparently the most radical ones. These voices summarise precisely the arguments and objections of the other critics. Firstly, the author looks at the exhortation as a whole and observes the role of the 8th chapter. He focuses on - for the critics - the most crucial passage in article 305, and especially in footnote 351. Then he deals with the so-called four cardinals' Dubia from November 2016 and with the comprehensive letter from summer 2017 titled Correctio filialis de haeresibus propagatis. Finally, he answers the questions asked in Dubia and Correctio, namely whether AL is contrarious to the traditional doctrine, to sacramentology, anthropology, or to the doctrine on the grace of God. [ABSTRACT FROM AUTHOR]

Plant photosystem II (PSII) is organized into large supercomplexes with variable levels of membrane-bound light-harvesting proteins (LHCIIs). The largest stable form of the PSII supercomplex involves four LHCII trimers, which are specifically connected to the PSII core dimer via monomeric antenna proteins. The PSII supercomplexes can further interact in the thylakoid membrane, forming PSII megacomplexes. So far, only megacomplexes consisting of two PSII supercomplexes associated in parallel have been observed. Here we show that the forms of PSII megacomplexes can be much more variable. We performed single particle electron microscopy (EM) analysis of PSII megacomplexes isolated from Arabidopsis thaliana using clear-native polyacrylamide gel electrophoresis. Extensive image analysis of a large data set revealed that besides the known PSII megacomplexes, there are distinct groups of megacomplexes with non-parallel association of supercomplexes. In some of them, we have found additional LHCII trimers, which appear to stabilize the non-parallel assemblies. We also performed EM analysis of the PSII supercomplexes on the level of whole grana membranes and successfully identified several types of megacomplexes, including those with non-parallel supercomplexes, which strongly supports their natural origin. Our data demonstrate a remarkable ability of plant PSII to form various larger assemblies, which may control photochemical usage of absorbed light energy in plants in a changing environment. [ABSTRACT FROM AUTHOR]

Photosynthesis in plants and algae relies on the coordinated function of photosystems ( PS) I and II. Their efficiency is augmented by finely-tuned light-harvesting proteins (Lhcs) connected to them. The most recent Lhcs (in evolutionary terms), Lhcb6 and Lhcb3, evolved during the transition of plants from water to land and have so far been considered to be an essential characteristic of land plants., We used single particle electron microscopy and sequence analysis to study architecture and composition of PSII supercomplex from Norway spruce and related species., We have found that there are major land plant families that lack functional lhcb6 and lhcb3 genes, which notably changes the organization of PSII supercomplexes. The Lhcb6 and Lhcb3 proteins have been lost in the gymnosperm genera Picea and Pinus (family Pinaceae) and Gnetum (Gnetales). We also revealed that the absence of these proteins in Norway spruce modifies the PSII supercomplex in such a way that it resembles its counterpart in the alga Chlamydomonas reinhardtii, an evolutionarily older organism., Our results break a deep-rooted concept of Lhcb6 and Lhcb3 proteins being the essential characteristic of land plants, and beg the question of what the evolutionary benefit of their loss could be. [ABSTRACT FROM AUTHOR]

The monomeric photosystem I-light-harvesting antenna complex I (PSI-LHCI) supercomplex from the extremophilic red alga Cyanidioschyzon merolae represents an intermediate evolutionary link between the cyanobacterial PSI reaction center and its green algal/higher plant counterpart. We show that the C. merolae PSI-LHCI supercomplex is characterized by robustness in various extreme conditions. By a combination of biochemical, spectroscopic, mass spectrometry, and electron microscopy/single particle analyses, we dissected three molecular mechanisms underlying the inherent robustness of the C. merolae PSI-LHCI supercomplex: (1) the accumulation of photoprotective zeaxanthin in the LHCI antenna and the PSI reaction center; (2) structural remodeling of the LHCI antenna and adjustment of the effective absorption cross section; and (3) dynamic readjustment of the stoichiometry of the two PSI-LHCI isomers and changes in the oligomeric state of the PSI-LHCI supercomplex, accompanied by dissociation of the PsaK core subunit. We show that the largest low light-treated C. merolae PSI-LHCI supercomplex can bind up to eight Lhcr antenna subunits, which are organized as two rows on the PsaF/PsaJ side of the core complex. Under our experimental conditions, we found no evidence of functional coupling of the phycobilisomes with the PSI-LHCI supercomplex purified from various light conditions, suggesting that the putative association of this antenna with the PSI supercomplex is absent or may be lost during the purification procedure. [ABSTRACT FROM AUTHOR]

Photosystem I (PSI) is a pigment-protein complex required for the light-dependent reactions of photosynthesis and participates in light-harvesting and redox-driven chloroplast metabolism. Assembly of PSI into supercomplexes with light harvesting complex (LHC) II, cytochrome b 6 f (Cytb 6 f) or NAD(P)H dehydrogenase complex (NDH) has been proposed as a means for regulating photosynthesis. However, structural details about the binding positions in plant PSI are lacking. We analyzed large data sets of electron microscopy single particle projections of supercomplexes obtained from the stroma membrane of Arabidopsis thaliana . By single particle analysis, we established the binding position of Cytb 6 f at the antenna side of PSI. The rectangular-shaped Cytb 6 f dimer binds at the side where Lhca1 is located. The complex binds with its short side rather than its long side to PSI, which may explain why these supercomplexes are difficult to purify and easily disrupted. Refined analysis of the interaction between PSI and the NDH complex indicates that in total up to 6 copies of PSI can arrange with one NDH complex. Most PSI-NDH supercomplexes appeared to have 1–3 PSI copies associated. Finally, the PSI-LHCII supercomplex was found to bind an additional LHCII trimer at two positions on the LHCI side in Arabidopsis. The organization of PSI, either in a complex with NDH or with Cytb 6 f, may improve regulation of electron transport by the control of binding partners and distances in small domains. [ABSTRACT FROM AUTHOR]

Gymnosperms, unlike angiosperms, are able to synthesize chlorophyll and form photosystems in complete darkness. Photosystem I (PSI) formed under such conditions is fully active, but photosystem II (PSII) is present in its latent form with inactive oxygen evolving complex (OEC). In this work we have studied light-induced gradual changes in PSII function in dark-grown cotyledons of Norway spruce ( Picea abies ) via the measurement of chlorophyll a fluorescence rise, absorption changes at 830 nm, thermoluminescence glow curves (TL) and protein analysis. The results indicate that in dark-grown cotyledons, alternative reductants were able to act as electron donors to PSII with inactive OEC. Illumination of cotyledons for 5 min led to partial activation of PSII, which was accompanied by detectable oxygen evolution, but still a substantial number of PSII centers remained in the so called PSII-Q B -non-reducing form. Interestingly, even 24 h long illumination was not sufficient for the full activation of PSII centers. This was evidenced by a weak attachment of PsbP protein and the absence of PsbQ protein in PSII particles, the absence of PSII supercomplexes, the suboptimal maximum yield of PSII photochemistry, the presence of C band in TL curve and also the presence of up-shifted Q band in TL in DCMU-treated cotyledons. This slow light-induced activation of PSII in dark-grown cotyledons could contribute to the prevention of PSII overexcitation before the light-induced increase in PSI/PSII ratio allows effective operation of linear electron flow. [ABSTRACT FROM AUTHOR]

Cyclic electron transport ( CET) around photosystem I ( PSI) plays an important role in balancing the ATP/ NADPH ratio and the photoprotection of plants. The NAD(P)H dehydrogenase complex ( NDH) has a key function in one of the CET pathways. Current knowledge indicates that, in order to fulfill its role in CET, the NDH complex needs to be associated with PSI; however, until now there has been no direct structural information about such a supercomplex. Here we present structural data obtained for a plant PSI- NDH supercomplex. Electron microscopy analysis revealed that in this supercomplex two copies of PSI are attached to one NDH complex. A constructed pseudo-atomic model indicates asymmetric binding of two PSI complexes to NDH and suggests that the low-abundant Lhca5 and Lhca6 subunits mediate the binding of one of the PSI complexes to NDH. On the basis of our structural data, we propose a model of electron transport in the PSI- NDH supercomplex in which the association of PSI to NDH seems to be important for efficient trapping of reduced ferredoxin by NDH. [ABSTRACT FROM AUTHOR]

The largest stable photosystem II (PSII) supercomplex in land plants (C2S2M2) consists of a core complex dimer (C2), two strongly (S2) and two moderately (M2) bound light-harvesting protein (LHCB) trimers attached to C2 via monomeric antenna proteins LHCB4-6. Recently, we have shown that LHCB3 and LHCB6, presumably essential for land plants, are missing in Norway spruce (Picea abies), which results in a unique structure of its C2S2M2 supercomplex. Here, we performed structure-function characterization of PSII supercomplexes in Arabidopsis (Arabidopsis thaliana) mutants lhcb3, lhcb6, and lhcb3 lhcb6 to examine the possibility of the formation of the "spruce-type" PSII supercomplex in angiosperms. Unlike in spruce, in Arabidopsis both LHCB3 and LHCB6 are necessary for stable binding of the M trimer to PSII core. The "spruce-type" PSII supercomplex was observed with low abundance only in the lhcb3 plants and its formation did not require the presence of LHCB4.3, the only LHCB4-type protein in spruce. Electron microscopy analysis of grana membranes revealed that the majority of PSII in lhcb6 and namely in lhcb3 lhcb6 mutants were arranged into C2S2 semi-crystalline arrays, some of which appeared to structurally restrict plastoquinone diffusion. Mutants without LHCB6 were characterized by fast induction of non-photochemical quenching and, on the contrary to the previous lhcb6 study, by only transient slowdown of electron transport between PSII and PSI. We hypothesize that these functional changes, associated with the arrangement of PSII into C2S2 arrays in thylakoids, may be important for the photoprotection of both PSI and PSII upon abrupt high-light exposure. [ABSTRACT FROM AUTHOR]