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AbstractUltrastructural changes and visual symptoms resulting from nutritional disorders involving boron, manganese, iron, zinc, copper, molybdenum, and nickel depend on the species of the plant, and are unknown in passion fruit plants (Passiflora edulis Sims). A hydroponic experiment evaluated the symptoms of nickel addition and micronutrient deficiency in passion fruit seedlings “BRS Gigante Amarelo” and determined the micronutrient contents in leaf and root tissue, root development, ultrastructural changes (leaf tissue deformations) and dry matter accumulation when visual symptoms were observed. Results showed that the order of manifestation of deficiencies was Fe > Mn > Zn > Cu > Mo > B. Nickel toxicity appeared 40 days after the experiment was started, presenting chlorosis in the new leaves followed by general yellowing and some white parts. Boron omission of resulted in deformations in the leaf limbus and loss of apical dominance, showing deformation of the growth points. Mn omission caused reduction of growth and generalized chlorosis of young leaves with a thick reticulum. Iron omission of resulted in internerval chlorosis with a fine lattice appearance. Omission of zinc and copper resulted in deformation and elongation of the leaves, reducing height and root development. Molybdenum omission caused chlorosis in the older leaves, which was observed to spread over time. Iron was the nutrient that most reflected symptoms of deficiency by the formation of root hairs. The findings of this research suggest that the knowledgement of plant micronutrients status permits an understanding of the physiological responses of passion fruit plants to crop fertilization. [ABSTRACT FROM AUTHOR]

Prevalent interactions among marine phytoplankton triggered by long‐range climatic stressors are well‐known environmental disturbers of community structure. Dynamic response of phytoplankton physiology is likely to come from interspecies interactions rather than direct climatic effect on single species. However, studies on enigmatic interactions among interspecies, which are induced by bioactive extracellular compounds (BECs), especially between related harmful algae sharing similar shellfish toxins, are scarce. Here, we investigated how BECs provoke the interactions between two notorious algae, Alexandrium minutum and Gymnodinium catenatum, which have similar paralytic shellfish toxin (PST) profiles. Using techniques including electron microscopy and transcriptome analysis, marked disruptions in G. catenatum intracellular microenvironment were observed under BECs pressure, encompassing thylakoid membrane deformations, pyrenoid matrix shrinkage and starch sheaths disappearance. In addition, the upregulation of gene clusters responsible for photosystem‐I Lhca1/4 and Rubisco were determined, leading to weaken photon captures and CO2 assimilation. The redistribution of lipids and proteins occurred at the subcellular level based on in situ focal plane array FTIR imaging approved the damages. Our findings illuminated an intense but underestimated interspecies interaction triggered by BECs, which is responsible for dysregulating photosynthesis and organelle function in inferior algae and may potentially account for fitness alteration in phytoplankton community. Summary statement: The bioactive extracellular compounds of Alexandrium minutum can induce interspecies interaction by affecting the cell physiology of related harmful algae, mainly showing damage to photosynthetic organelles and redistribution of intracellular biomacromolecules. [ABSTRACT FROM AUTHOR]

"Drawing inspiration from nature" offers a wealth of creative possibilities for designing cutting‐edge materials with improved properties and performance. Nature‐inspired thylakoid‐based nanoarchitectures, seamlessly integrate the inherent structures and functions of natural components with the diverse and controllable characteristics of nanotechnology. These innovative biomaterials have garnered significant attention for their potential in various biomedical applications. Thylakoids possess fundamental traits such as light harvesting, oxygen evolution, and photosynthesis. Through the integration of artificially fabricated nanostructures with distinct physical and chemical properties, novel photosynthetic nanoarchitectures can be catalytically generated, offering versatile functionalities for diverse biomedical applications. In this article, an overview of the properties and extraction methods of thylakoids are provided. Additionally, the recent advancements in the design, preparation, functions, and biomedical applications of a range of thylakoid‐based photosynthetic nanoarchitectures are reviewed. Finally, the foreseeable challenges and future prospects in this field is discussed. [ABSTRACT FROM AUTHOR]

Abiotic stress is triggered by unfavorable environments such as drought, severe heat, heavy metals, soil saturation, high-intensity light, and high salinity. These, in turn greatly affect photosynthesis, which has a large effect on the growth and development of plants. Plant survival in a changing environment depends on the ability of the plant to rapidly adjust its metabolism and photosynthetic processes. For a long time, it has been known that the thylakoid and its lumen play a crucial role in plant responses to the environment in terms of oxygen evolution, electron transfer, and photoprotection. Abiotic stress has a direct effect on photosynthetic activity by disrupting all photosynthetic processes, such as both photosystems I (PSI) and II (PSII), electron transport, carbon fixation, ATP generation, and stomatal conductance. Thylakoid-bound proteins have recently been discovered to play roles in a variety of physiological processes, most notably in the modulation of thylakoid biogenesis, as well as the photosynthetic protein complexes' activity and turnover. These proteins are particularly important in controlling photosystem I, photosystem II, NAD(P)H dehydrogenase-like complexes, and response to various abiotic stresses. According to the proteome study, the thylakoid contains at least 335 different proteins in Arabidopsis thaliana. However, the roles of the majority of thylakoid and lumen proteins involved in oxidative stress remain unknown. This review provides an in-depth analysis at the thylakoid-bound proteins and discusses how various genes get modulated in response to the abiotic stresses. [ABSTRACT FROM AUTHOR]

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A structural re-modeling of the thylakoid system, including granum size and regularity, occurs in chlorophyll-deficient wheat mutants affected by photosynthetic membrane over-reduction. In the chloroplast of land plants, the thylakoid system is defined by appressed grana stacks and unstacked stroma lamellae. This study focuses on the variations of the grana organization occurring in outdoor-grown wheat mutants characterized by low chlorophyll content and a tendency for photosynthetic membrane over-reduction. Triticum aestivum ANK-32A and Triticum durum ANDW-7B were compared to their corresponding WT lines, NS67 and LD222, respectively. Electron micrographs of chloroplasts were used to calculate grana ultrastructural parameters. Photosynthetic parameters were obtained by modulated chlorophyll fluorescence and applying Light Curves (LC) and Rapid Light Curves (RLC) protocols. For each photosynthetic parameter, the difference Δ(RLC-LC) was calculated to evaluate the flexible response to light in the examined lines. In the mutants, fewer and smaller disks formed grana stacks characterized by a marked increase in lateral and cross-sectional irregularity, both negatively correlated with the number of layers per granum. A relationship was found between membrane over-reduction and granum structural irregularity. The possible acclimative significance of a greater proportion of stroma-exposed grana domains in relieving the excess electron pressure on PSI is discussed. [ABSTRACT FROM AUTHOR]

Atherosclerosis is the most common cause of cardiovascular diseases that contribute to the major morbidity worldwide, but still lacking of effective treatment strategy. Here, a hybrid cell is constructed for the sonodynamic effect promoted cell therapy of early atherosclerosis by fusing M2 macrophages with thylakoid (TK) membranes. After systemic administration, the obtained TK-M2 actively accumulates in the early atherosclerotic plaques, wherein M2 macrophages relieve the cholesterol accumulation and the inflammation in the foam cells. Meanwhile, the TK membranes decorated on the M2 macrophages exhibit both type I and type II sonodynamic effects under ultrasound (US) activation, inducing the direct apoptosis of foam cells. The cooperation of M2 and TK leads to significant outcome in eliminating atherosclerotic plaques without obvious side-effects, providing a new avenue for atherosclerosis treatment. [ABSTRACT FROM AUTHOR]

Thylakoid membranes are energy-converting membranes with a unique lipid composition. Though the membranes are primarily composed of proteins, their photosynthetic function is strongly influenced by the lipid constituents. Here we characterize, with molecular dynamics (MD) simulations, lipid bilayers with compositions representative of plant thylakoid membranes. We determine, in a wide range of temperatures, the physical parameters of the model membranes which are relevant for the photosynthetic function. We found a marked impact of temperature on membrane permeability due to a combination of increased compressibility and curvature of the membrane at elevated temperatures. With increasing temperatures, we observed increasingly smeared transmembrane density profiles of the membrane forming lipid headgroups predicting increased membrane flexibility. The diffusion coefficient of the lipids increased with temperature without apparent specificity for lipid species. Instead of a comprehensive experimental dataset in the relevant temperature range, we quantitatively compared and validated our MD results with MD simulations on a dipalmitoylphosphatidylcholine model system.

Within the ancient vascular plant lineage known as lycophytes, many Selaginella species contain only one giant chloroplast in the upper epidermal cells of the leaf. In deep-shade species, such as S. martensii, the chloroplast is cup-shaped and the thylakoid system differentiates into an upper lamellar region and a lower granal region (bizonoplast). In this report, we describe the ultrastructural changes occurring in the giant chloroplast hosted in the epidermal cells of S. martensii during the daily relocation of the organelle. The process occurs in up to ca. 40% of the microphylls without the plants being exposed to high-light flecks. The relocated chloroplast loses its cup shape: first, it flattens laterally toward the radial cell wall and then assumes a more globular shape. The loss of the conical cell shape, the side-by-side lateral positioning of vacuole and chloroplast, and the extensive rearrangement of the thylakoid system to only granal cooperate in limiting light absorption. While the cup-shaped chloroplast emphasizes the light-harvesting capacity in the morning, the relocated chloroplast is suggested to support the renewal of the thylakoid system during the afternoon, including the recovery of photosystem II (PSII) from photoinhibition. The giant chloroplast repositioning is part of a complex reversible reshaping of the whole epidermal cell. [ABSTRACT FROM AUTHOR]

The molecular identification of maize dwarf mosaic virus (MDMV) and its effects on the morphophysiological traits of maize (Zea mays L.) was the focus of the presented research, intending to study the activity dynamics of two main types of enzymes, peroxidases, weakly binding to the membrane, and soluble peroxidases. The molecular identification of the virus engaged the use of the RT-PCR method. Results revealed that in the climatic conditions of Uzbekistan, red necrotic spotting, yellow mosaic with a large border on the edge of the leaf, curling of the leaves, yellow striped mosaic, and short stature all appeared in the maize plants. According to previous symptoms, the visual diagnostic methods used determine the maize yellow mosaic virus indications. In the existing study, the gene responsible for the protein coat synthesis (SR) nucleotide sequence served to diagnose the MDMV, and as a result, PCR tests showed yellow streaks on the leaves of maize plants. The mosaic and motility symptoms have been characteristic proofs of MDMV. The MDMV infects the maize plants in the initial growth phase (3-5 leaves), then the symptoms appear after a few days. Through morphological indicators, viral disease identification is possible at subsequent stages (6-7 leaves). Using spectrophotometry, the peroxidase enzyme activity in maize plants receives the virus infection to determine an early level of infectivity. The results confirmed that, in infected maize plants, peroxidase associated with the cell membrane was much more active than in control plants. It proves that contaminated Zea mays plants were in a stressful situation due to the virus. The RT-PCR method, widely used in diagnostics, sought to identify the virus species affiliation. PCR proceeded based on the virus coat protein (CP) gene. [ABSTRACT FROM AUTHOR]

Photosynthetic electron transfer and its regulation processes take place on thylakoid membranes, and the thylakoid of vascular plants exhibits particularly intricate structure consisting of stacked grana and flat stroma lamellae. It is known that several membrane remodeling proteins contribute to maintain the thylakoid structure, and one putative example is FUZZY ONION LIKE (FZL). In this study, we re-evaluated the controversial function of FZL in thylakoid membrane remodeling and in photosynthesis. We investigated the sub-membrane localization of FZL and found that it is enriched on curved grana edges of thylakoid membranes, consistent with the previously proposed model that FZL mediates fusion of grana and stroma lamellae at the interfaces. The mature fzl thylakoid morphology characterized with the staggered and less connected grana seems to agree with this model as well. In the photosynthetic analysis, the fzl knockout mutants in Arabidopsis displayed reduced electron flow, likely resulting in higher oxidative levels of Photosystem I (PSI) and smaller proton motive force (pmf). However, nonphotochemical quenching (NPQ) of chlorophyll fluorescence was excessively enhanced considering the pmf levels in fzl, and we found that introducing kea3-1 mutation, lowering pH in thylakoid lumen, synergistically reinforced the photosynthetic disorder in the fzl mutant background. We also showed that state transitions normally occurred in fzl, and that they were not involved in the photosynthetic disorders in fzl. We discuss the possible mechanisms by which the altered thylakoid morphology in fzl leads to the photosynthetic modifications. [ABSTRACT FROM AUTHOR]

A deeper understanding of the mechanisms underlying impaired sugarcane performance (Saccharum spp.) under nitrogen (N) deficiency might help select targeted traits for developing N-efficient genotypes. In this regard, we focused on the study of the effects of low-N stress on mesophyll chloroplast integrity and its relationship with shoot growth traits. Plants were grown in sand culture under varying N supply (1.5, 3.0, 6.0 and 12.0 mM of N) for 60 days, when mature leaves were sampled for transmission electron microscopy analysis. Then, the number of tillers was counted and shoot was harvested to estimate leaf area, dry mass production and leaf N concentration. Images of transmission electron microscopy revealed pronounced damages exclusively to the ultrastructure of mesophyll chloroplast in the severely N-deficient plants (1.5 mM of N), including thylakoid membrane disarrangement and poorly stacked grana. Tillering, leaf area, shoot dry mass and leaf N concentration increased as function of nutrient supply. However, maximum values of these parameters were attained at higher N availability (9.1–9.9 mM of N) than that related to the maintenance of mesophyll chloroplast integrity. Our results suggest, hence, that impairments in the ultrastructure of this organelle plays a key role on poor sugarcane biomass production only under severe N deficiency condition. This finding adds insights into the reasons of impaired sugarcane performance under low-N stress and might assist the selection of suitable traits to be sought in N-efficient genotypes. [ABSTRACT FROM AUTHOR]

Introduction: Iron (Fe) is one of themost important cofactors in the photosynthetic apparatus, and its uptake by chloroplasts has also been associated with the operation of the photosynthetic electron transport chain during reduction-based plastidial Fe uptake. Therefore, plastidial Fe uptake was considered not to be operational in the absence of the photosynthetic activity. Nevertheless, Fe is also required for enzymatic functions unrelated to photosynthesis, highlighting the importance of Fe acquisition by non-photosynthetic plastids. Yet, it remains unclear how these plastids acquire Fe in the absence of photosynthetic function. Furthermore, plastids of etiolated tissues should already possess the ability to acquire Fe, since the biosynthesis of thylakoid membrane complexes requires a massive amount of readily available Fe. Thus, we aimed to investigate whether the reduction-based plastidial Fe uptake solely relies on the functioning photosynthetic apparatus. Methods: In our combined structure, iron content and transcript amount analysis studies, we used Savoy cabbage plant as a model, which develops natural etiolation in the inner leaves of the heads due to the shading of the outer leaf layers. Results: Foliar and plastidial Fe content of Savoy cabbage leaves decreased towards the inner leaf layers. The leaves of the innermost leaf layers proved to be etiolated, containing etioplasts that lacked the photosynthetic machinery and thus were photosynthetically inactive. However, we discovered that these etioplasts contained, and were able to take up, Fe. Although the relative transcript abundance of genes associated with plastidial Fe uptake and homeostasis decreased towards the inner leaf layers, both ferric chelate reductase FRO7 transcripts and activity were detected in the innermost leaf layer. Additionally, a significant NADP(H) pool and NAD(P)H dehydrogenase activity was detected in the etioplasts of the innermost leaf layer, indicating the presence of the reducing capacity that likely supports the reduction-based Fe uptake of etioplasts. Discussion: Based on these findings, the reduction-based plastidial Fe acquisition should not be considered exclusively dependent on the photosynthetic functions. [ABSTRACT FROM AUTHOR]

Summary: An increasing number of small proteins has been identified in the genomes of well‐annotated organisms, including the model cyanobacterium Synechocystis sp. PCC 6803. We describe a newly assigned protein comprising 37 amino acids that is encoded upstream of the superoxide dismutase SodB encoding gene.To clarify the role of SliP4, we analyzed a Synechocystis sliP4 mutant and a strain containing a fully active, Flag‐tagged variant of SliP4 (SliP4.f).The initial hypothesis that this small protein might be functionally related to SodB could not be supported. Instead, we provide evidence that it fulfills important functions related to the organization of photosynthetic complexes. Therefore, we named it a small light‐induced protein of 4 kDa, SliP4. This protein is strongly induced under high‐light conditions. The lack of SliP4 causes a light‐sensitive phenotype due to impaired cyclic electron flow and state transitions. Interestingly, SliP4.f was co‐isolated with NDH1 complex and both photosystems. The interaction between SliP4.f and all three types of complexes was further confirmed by additional pulldowns and 2D‐electrophoreses.We propose that the dimeric SliP4 serves as a molecular glue promoting the aggregation of thylakoid complexes, which contributes to different electron transfer modes and energy dissipation under stress conditions. [ABSTRACT FROM AUTHOR]

Thylakoid membranes are energy-converting membranes with a unique lipid composition. Though the membranes are primarily composed of proteins, their photosynthetic function is strongly influenced by the lipid constituents. Here we characterize, with molecular dynamics (MD) simulations, lipid bilayers with compositions representative of plant thylakoid membranes. We determine, in a wide range of temperatures, the physical parameters of the model membranes which are relevant for the photosynthetic function. We found a marked impact of temperature on membrane permeability due to a combination of increased compressibility and curvature of the membrane at elevated temperatures. With increasing temperatures, we observed increasingly smeared transmembrane density profiles of the membrane forming lipid headgroups predicting increased membrane flexibility. The diffusion coefficient of the lipids increased with temperature without apparent specificity for lipid species. Instead of a comprehensive experimental dataset in the relevant temperature range, we quantitatively compared and validated our MD results with MD simulations on a dipalmitoylphosphatidylcholine model system. [ABSTRACT FROM AUTHOR]

Biotic and abiotic stresses are among major factors limiting crop yields, and Filamentation temperature-sensitive (FtsH) genes are one of the key regulators of plant response to these stresses. The FtsH is an ATP-dependent metalloprotease in prokaryotes and eukaryotes. Due to the economic importance and cultivation of potato grown in the biotic and abiotic stress prone areas, identification and characterization of FtsH family members are crucially important. The present research was conducted to investigate FtsH family members in potato under stressful regime. To detect the FtsH genes in potato, we performed genome-wide analysis of FtsH genes in the Solanum tuberosum genome using the Ensemble Plant. All putative sequences were approved with the Pfam. Bioinformatics analysis was conducted using phylogenetic tree, gene structure, Transcription factor-binding site (TFBS) analysis, protein–protein interaction, and gene expression. The members of FtsH were categorized into eight groups. Some of the FtsH proteins were subcellularly located in the nucleus and chloroplast. The number of introns was ranged from 3 to 14 in gene family members. Totally, 33 TFBS including biotic and abiotic stress-responsive elements were found in FtsH promoter sequences. MYB and WRKY were the highest number among TFBS which were involved in abiotic and biotic stresses. Gene expression analysis revealed that the StFtsH2 and StFtsH5 had the highest gene expression, induced by abiotic and biotic stresses in all three tissues of stem, root, and leaves. It is expected that the StFtsH2 and StFtsH5 could be used in plant manipulation and breeding programs aimed for tolerance enhancement to abiotic (cold, heat, and high light) and biotic stresses [Potato virus Y (PVY), Potato virus X (PVX), Potato virus A (PVA), Potato virus X (PVA), and Potato virus S (PVS)]. [ABSTRACT FROM AUTHOR]

SUMMARY: Plants respond to changing light intensity in the short term through regulation of light harvesting, electron transfer, and metabolism to mitigate redox stress. A sustained shift in light intensity leads to a long‐term acclimation response (LTR). This involves adjustment in the stoichiometry of photosynthetic complexes through de novo synthesis and degradation of specific proteins associated with the thylakoid membrane. The light‐harvesting complex II (LHCII) serine/threonine kinase STN7 plays a key role in short‐term light harvesting regulation and was also suggested to be crucial to the LTR. Arabidopsis plants lacking STN7 (stn7) shifted to low light experience higher photosystem II (PSII) redox pressure than the wild type or those lacking the cognate phosphatase TAP38 (tap38), while the reverse is true at high light, where tap38 suffers more. In principle, the LTR should allow optimisation of the stoichiometry of photosynthetic complexes to mitigate these effects. We used quantitative label‐free proteomics to assess how the relative abundance of photosynthetic proteins varied with growth light intensity in wild‐type, stn7, and tap38 plants. All plants were able to adjust photosystem I, LHCII, cytochrome b6f, and ATP synthase abundance with changing white light intensity, demonstrating neither STN7 nor TAP38 is crucial to the LTR per se. However, stn7 plants grown for several weeks at low light (LL) or moderate light (ML) still showed high PSII redox pressure and correspondingly lower PSII efficiency, CO2 assimilation, and leaf area compared to wild‐type and tap38 plants, hence the LTR is unable to fully ameliorate these symptoms. In contrast, under high light growth conditions the mutants and wild type behaved similarly. These data are consistent with the paramount role of STN7‐dependent LHCII phosphorylation in tuning PSII redox state for optimal growth in LL and ML conditions. Significance Statement: The light harvesting complex II (LHCII) serine/threonine kinase STN7 has been previously implicated in both short‐term light harvesting regulation and the long‐term acclimation response (LTR). Here, using label‐free quantitative proteomics we show that plants lacking STN7 are capable of adjusting the stoichiometry of photosynthetic complexes via the LTR, but still suffer a growth penalty in low and moderate light resulting from the loss of light harvesting regulation. [ABSTRACT FROM AUTHOR]

The photosynthetic capacity of chloroplasts is vital for autotrophic growth in algae and plants. The origin of the chloroplast has been explained by the endosymbiotic theory that proposes the engulfment of a cyanobacterium by an ancestral eukaryotic cell followed by the transfer of many cyanobacterial genes to the host nucleus. As a result of the gene transfer, the now nuclear-encoded proteins acquired chloroplast targeting peptides (known as transit peptides; transit peptide) and are translated as preproteins in the cytosol. Transit peptides contain specific motifs and domains initially recognized by cytosolic factors followed by the chloroplast import components at the outer and inner envelope of the chloroplast membrane. Once the preprotein emerges on the stromal side of the chloroplast protein import machinery, the transit peptide is cleaved by stromal processing peptidase. In the case of thylakoid-localized proteins, cleavage of the transit peptides may expose a second targeting signal guiding the protein to the thylakoid lumen or allow insertion into the thylakoid membrane by internal sequence information. This review summarizes the common features of targeting sequences and describes their role in routing preproteins to and across the chloroplast envelope as well as the thylakoid membrane and lume [ABSTRACT FROM AUTHOR]

IntroductionIron (Fe) is one of themost important cofactors in the photosynthetic apparatus, and its uptake by chloroplasts has also been associated with the operation of the photosynthetic electron transport chain during reduction-based plastidial Fe uptake. Therefore, plastidial Fe uptake was considered not to be operational in the absence of the photosynthetic activity. Nevertheless, Fe is also required for enzymatic functions unrelated to photosynthesis, highlighting the importance of Fe acquisition by non-photosynthetic plastids. Yet, it remains unclear how these plastids acquire Fe in the absence of photosynthetic function. Furthermore, plastids of etiolated tissues should already possess the ability to acquire Fe, since the biosynthesis of thylakoid membrane complexes requires a massive amount of readily available Fe. Thus, we aimed to investigate whether the reduction-based plastidial Fe uptake solely relies on the functioning photosynthetic apparatus.MethodsIn our combined structure, iron content and transcript amount analysis studies, we used Savoy cabbage plant as a model, which develops natural etiolation in the inner leaves of the heads due to the shading of the outer leaf layers.ResultsFoliar and plastidial Fe content of Savoy cabbage leaves decreased towards the inner leaf layers. The leaves of the innermost leaf layers proved to be etiolated, containing etioplasts that lacked the photosynthetic machinery and thus were photosynthetically inactive. However, we discovered that these etioplasts contained, and were able to take up, Fe. Although the relative transcript abundance of genes associated with plastidial Fe uptake and homeostasis decreased towards the inner leaf layers, both ferric chelate reductase FRO7 transcripts and activity were detected in the innermost leaf layer. Additionally, a significant NADP(H) pool and NAD(P)H dehydrogenase activity was detected in the etioplasts of the innermost leaf layer, indicating the presence of the reducing capacity that likely supports the reduction-based Fe uptake of etioplasts.DiscussionBased on these findings, the reduction-based plastidial Fe acquisition should not be considered exclusively dependent on the photosynthetic functions.

The photosynthetic capacity of chloroplasts is vital for autotrophic growth in algae and plants. The origin of the chloroplast has been explained by the endosymbiotic theory that proposes the engulfment of a cyanobacterium by an ancestral eukaryotic cell followed by the transfer of many cyanobacterial genes to the host nucleus. As a result of the gene transfer, the now nuclear-encoded proteins acquired chloroplast targeting peptides (known as transit peptides; transit peptide) and are translated as preproteins in the cytosol. Transit peptides contain specific motifs and domains initially recognized by cytosolic factors followed by the chloroplast import components at the outer and inner envelope of the chloroplast membrane. Once the preprotein emerges on the stromal side of the chloroplast protein import machinery, the transit peptide is cleaved by stromal processing peptidase. In the case of thylakoid-localized proteins, cleavage of the transit peptides may expose a second targeting signal guiding the protein to the thylakoid lumen or allow insertion into the thylakoid membrane by internal sequence information. This review summarizes the common features of targeting sequences and describes their role in routing preproteins to and across the chloroplast envelope as well as the thylakoid membrane and lumen.

Photosystem II (PSII) of the photosynthetic apparatus in oxygenic organisms contains a catalytic center that performs one of the most important reactions in bioenergetics: light-dependent water oxidation to molecular oxygen. The catalytic center is a Mn4CaO5 cluster consisting of four cations of manganese and one calcium cation linked by oxygen bridges. The authors reported earlier that a structural transition occurs at pH 5.7 in the cluster resulting in changes in manganese cation(s) redox potential and elevation of the Mn‑clus-ter resistance to reducing agents. The discovered effect was examined in a series of investigations that are reviewed in this work. It was found that, at pH 5.7, Fe(II) cations replace not two manganese cations as it happens at pH 6.5 but only one cation; as a result, a chimeric Mn3Fe1 cluster is produced. In the presence of exogenous calcium ions, membrane preparations of PSII with such a chimeric cluster are capable of evolving oxygen in the light (at a rate of approximately 25% of the rate in native PSII). It was found that photoinhibition that greatly depends on the processes of oxidation or reduction at pH 5.7 slows down as compared with pH 6.5. PSII preparations were also more resistant to thermal inactivation at pH 5.7 than at pH 6.5. However, in PSII preparations lacking manganese cations in the oxygen-evolving complex, the rates of photoinhibition at pH 6.5 and 5.7 did not differ. In thylakoid membranes, protonophores that abolish the proton gradient and increase pH in the lumen (where the manganese cluster is located) from 5.7 to 7.0 considerably elevated the rate of PSII photoinhibition. It is assumed that the structural transition in the Mn-cluster at pH 5.7 is involved in the mechanisms of PSII defense against photoinhibition. [ABSTRACT FROM AUTHOR]

Photosynthetic capacity is usually affected by light intensity in the field. In this study, photosynthetic characteristics of four different Triticeae crops (wheat, triticale, barley, and highland barley) were investigated based on chlorophyll fluorescence and the level of photosynthetic proteins under high light. Compared with wheat, three cereals (triticale, barley, and highland barley) presented higher photochemical efficiency and heat dissipation under normal light and high light for 3 h, especially highland barley. In contrast, lower photoinhibition was observed in barley and highland barley relative to wheat and triticale. In addition, barley and highland barley showed a lower decline in D1 and higher increase in Lhcb6 than wheat and triticale under high light. Furthermore, compared with the control, the results obtained from PSII protein phosphorylation showed that the phosphorylation level of PSII reaction center proteins (D1 and D2) was higher in barley and highland barley than that of wheat and triticale. Therefore, we speculated that highland barley can effectively alleviate photodamages to photosynthetic apparatus by high photoprotective dissipation, strong phosphorylation of PSII reaction center proteins, and rapid PSII repair cycle under high light. [ABSTRACT FROM AUTHOR]

FtsH proteases are membrane-embedded proteolytic complexes important for protein quality control and regulation of various physiological processes in bacteria, mitochondria, and chloroplasts. Like most cyanobacteria, the model species Synechocystis sp. PCC 6803 contains four FtsH homologs, FtsH1–FtsH4. FtsH1–FtsH3 form two hetero-oligomeric complexes, FtsH1/3 and FtsH2/3, which play a pivotal role in acclimation to nutrient deficiency and photosystem II quality control, respectively. FtsH4 differs from the other three homologs by the formation of a homo-oligomeric complex, and together with Arabidopsis thaliana AtFtsH7/9 orthologs, it has been assigned to another phylogenetic group of unknown function. Our results exclude the possibility that Synechocystis FtsH4 structurally or functionally substitutes for the missing or non-functional FtsH2 subunit in the FtsH2/3 complex. Instead, we demonstrate that FtsH4 is involved in the biogenesis of photosystem II by dual regulation of high light-inducible proteins (Hlips). FtsH4 positively regulates expression of Hlips shortly after high light exposure but is also responsible for Hlip removal under conditions when their elevated levels are no longer needed. We provide experimental support for Hlips as proteolytic substrates of FtsH4. Fluorescent labeling of FtsH4 enabled us to assess its localization using advanced microscopic techniques. Results show that FtsH4 complexes are concentrated in well-defined membrane regions at the inner and outer periphery of the thylakoid system. Based on the identification of proteins that co-purified with the tagged FtsH4, we speculate that FtsH4 concentrates in special compartments in which the biogenesis of photosynthetic complexes takes place.

Summary: In higher plants, photosystems II and I are found in grana stacks and unstacked stroma lamellae, respectively. To connect them, electron carriers negotiate tortuous multi‐media paths and are subject to macromolecular blocking. Why does evolution select an apparently unnecessary, inefficient bipartition? Here we systematically explain this perplexing phenomenon. We propose that grana stacks, acting like bellows in accordions, increase the degree of ultrastructural control on photosynthesis through thylakoid swelling/shrinking induced by osmotic water fluxes. This control coordinates with variations in stomatal conductance and the turgor of guard cells, which act like an accordion's air button. Thylakoid ultrastructural dynamics regulate macromolecular blocking/collision probability, direct diffusional pathlengths, division of function of Cytochrome b6f complex between linear and cyclic electron transport, luminal pH via osmotic water fluxes, and the separation of pH dynamics between granal and lamellar lumens in response to environmental variations. With the two functionally asymmetrical photosystems located distantly from each other, the ultrastructural control, nonphotochemical quenching, and carbon‐reaction feedbacks maximally cooperate to balance electron transport with gas exchange, provide homeostasis in fluctuating light environments, and protect photosystems in drought. Grana stacks represent a dry/high irradiance adaptation of photosynthetic machinery to improve fitness in challenging land environments. Our theory unifies many well‐known but seemingly unconnected phenomena of thylakoid structure and function in higher plants. [ABSTRACT FROM AUTHOR]

Summary: The nucleotides guanosine tetraphosphate and pentaphosphate (or (p)ppGpp) are implicated in the regulation of chloroplast function in plants. (p)ppGpp signalling is best understood in the model vascular plant Arabidopsis thaliana in which it acts to regulate plastid gene expression to influence photosynthesis, plant development and immunity. However, little information is known about the conservation or diversity of (p)ppGpp signalling in other land plants.We studied the function of ppGpp in the moss Physcomitrium (previously Physcomitrella) patens using an inducible system for triggering ppGpp accumulation. We used this approach to investigate the effects of ppGpp on chloroplast function, photosynthesis and growth.We demonstrate that ppGpp accumulation causes a dramatic drop in photosynthetic capacity by inhibiting chloroplast gene expression. This was accompanied by the unexpected reorganisation of the thylakoid system into super grana. Surprisingly, these changes did not affect gametophore growth, suggesting that bryophytes and vascular plants may have different tolerances to defects in photosynthesis.Our findings point to the existence of both highly conserved and more specific targets of (p)ppGpp signalling in the land plants that may reflect different growth strategies. [ABSTRACT FROM AUTHOR]

Biohybrid devices that generate an electrical signal under the influence of light due to photochemical reactions in photosynthetic pigment-protein complexes have many prospects. On the one hand, the oxygen-evolving complex of photosystem II allows the use of ubiquitous water as a source of electrons for photoinduced electron transfer in such devices; on the other hand, it is the most vulnerable part of the photosynthetic apparatus. From the perspective of sustainable operation of bio-based hybrid devices, it is helpful to analyze how removing or modifying the Mn cluster will affect the performance of the bio-hybrid device. This work analyzed photocurrent generation in a liquid three-electrode solar cell based on manganese-depleted and reactivated thylakoid membranes. Membranes lacking Mn could not produce any significant photocurrent until manganese chloride was added. After adding MnCl 2 , the cell could produce current when exposed to light. This current was about a few percent from cells with intact thylakoid membranes. However, the photoactivation procedure made it possible to restore up to 75 % of the photocurrent of cells based on intact thylakoid membranes. The main objective of this work is to answer the question about the possibility of photocurrent generation in a biohybrid system based on thylakoid membranes using artificial analogs of the native oxygen-evolving complex. Photoactivation with manganese chloride is the simplest way to obtain preparations devoid of the native Mn cluster, but capable of oxidizing water., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Suleyman I. Allakhverdiev reports financial support was provided by Russian Science Foundation. Barry D. Bruce reports a relationship with National Science Foundation that includes: funding grants. Barry D. Bruce, Special Guest Editor, Applied Photosynthesis BBA- Bioenergetics Suleyman I. Allakhverdieve, Special Guest Editor, Applied Photosynthesis BBA- Bioenergetics If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

The light-sensitive (LS) albino tea plant grows albinic shoots lacking chlorophylls (Chls) under high-light (HL) conditions, and the albinic shoots re-green under low light (LL) conditions. The albinic shoots contain a high level of amino acids and are preferential materials for processing quality green tea. The young plants of the albino tea cultivars are difficult to be cultivated owing to lacking Chls. The mechanisms of the tea leaf bleaching and re-greening are unknown. We detected the activity and composition of photosystem II (PSII) subunits in LS albino tea cultivar "Huangjinya" (HJY), with a normal green-leaf cultivar "Jinxuan" (JX) as control so as to find the relationship of PSII impairment to the albino phenotype in tea. The PSII of HJY is more vulnerable to HL-stress than JX. HL-induced degradation of PSII subunits CP43, CP47, PsbP, PsbR. and light-harvest chlorophyll–protein complexes led to the exposure and degradation of D1 and D2, in which partial fragments of the degraded subunits were crosslinked to form larger aggregates. Two copies of subunits PsbO, psbN, and Lhcb1 were expressed in response to HL stress. The cDNA sequencing of CP43 shows that there is no difference in sequences of PsbC cDNA and putative amino acids of CP43 between HJY and JX. The de novo synthesis and/or repair of PSII subunits is considered to be involved in the impairment of PSII complexes, and the latter played a predominant role in the albino phenotype in the LS albino tea plant. [ABSTRACT FROM AUTHOR]

Symbiotic relationships are very important for corals. Abiotic stressors cause the acclimatization of cell membranes in symbionts, which possess different membrane acclimatization strategies. Membrane stability is determined by a unique lipid composition and, thus, the profile of thylakoid lipids can depend on coral symbiont species. We have analyzed and compared thylakoid lipidomes (mono- and digalactosyldiacylglycerols (MGDG and DGDG), sulfoquinovosyldiacylglycerols (SQDG), and phosphatidylglycerols (PG)) of crude extracts from symbiotic reef-building coral Acropora sp., the hydrocoral Millepora platyphylla, and the octocoral Sinularia flexibilis. S. flexibilis crude extracts were characterized by a very high SQDG/PG ratio, a DGDG/MGDG ratio < 1, a lower degree of galactolipid unsaturation, a higher content of SQDG with polyunsaturated fatty acids, and a thinner thylakoid membrane which may be explained by the presence of thermosensitive dinoflagellates Cladocopium C3. In contrast, crude extracts of M. platyphylla and Acropora sp. exhibited the lipidome features of thermotolerant Symbiodiniaceae. M. platyphylla and Acropora sp. colonies contained Cladocopium C3u and Cladocopium C71/C71a symbionts, respectively, and their lipidome profiles showed features that indicate thermotolerance. We suggest that an association with symbionts that exhibit the thermotolerant thylakoid lipidome features, combined with a high Symbiodiniaceae diversity, may facilitate further acclimatization/adaptation of M. platyphylla and Acropora sp. holobionts in the South China Sea. [ABSTRACT FROM AUTHOR]

Fibrillins (FBNs) are a family of genes in cyanobacteria, algae, and plants. The proteins they encode possess a lipid-binding motif, exist in various types of plastids, and are associated with lipid bodies called plastoglobules, implicating them in lipid metabolism. FBNs present in the thylakoid and stroma are involved in the storage, transport, and synthesis of lipid molecules for photoprotective functions against high-light stress. In this review, the diversity of subplastid locations in the evolution of FBNs, regulation of FBNs expression by various stresses, and the role of FBNs in plastid lipid metabolism are comprehensively summarized and directions for future research are discussed. [ABSTRACT FROM AUTHOR]

The appearance of oxygenic photosynthesis in cyanobacteria is a major event in evolution. It had an irreversible impact on the Earth, promoting the Great Oxygenation Event (GOE) ~2.4 billion years ago. Ancient cyanobacteria predating the GOE were Gloeobacter -type cells lacking thylakoids, which hosted photosystems in their cytoplasmic membrane. The driver of the GOE was proposed to be the transition from unicellular to filamentous cyanobacteria. However, the appearance of thylakoids expanded the photosynthetic surface to such an extent that it introduced a multiplier effect, which would be more coherent with an impact on the atmosphere. Primitive thylakoids self-organize as concentric parietal uninterrupted multilayers. There is no robust evidence for an origin of thylakoids via a vesicular-based scenario. This review reports studies supporting that hexagonal II-forming glucolipids and galactolipids at the periphery of the cytosolic membrane could be turned, within nanoseconds and without any external source of energy, into membrane multilayers. Comparison of lipid biosynthetic pathways shows that ancient cyanobacteria contained only one anionic lamellar-forming lipid, phosphatidylglycerol. The acquisition of sulfoquinovosyldiacylglycerol biosynthesis correlates with thylakoid emergence, possibly enabling sufficient provision of anionic lipids to trigger a hexagonal II-to-lamellar phase transition. With this non-vesicular lipid-phase transition, a framework is also available to re-examine the role of companion proteins in thylakoid biogenesis. [ABSTRACT FROM AUTHOR]

Thylakoid (Tk) membranes are of unique superiority in photodynamic therapy (PDT) because they not only carry abundant chlorophylls containing photosensitizer porphyrin but also can produce O2. However, the current therapeutic performance of Tk is dramatically limited because of their poor tumor targeting and inefficient O2 production. Here, we report an immunomodulatory bio-nanovesicle of Tk membranes fused with M1 macrophage-derived extracellular vesicles (M1 EV) for efficient PDT of tumors. The hybrid nanovesicle Tk@M1 was prepared by squeezing the Tk membranes of spinach with M1 EV. The systemic study confirmed that Tk@M1 can not only actively accumulate in tumors but also effectively regulate the inactive immune microenvironment of tumors. Such activated "hot" tumors significantly enhance the PDT efficacy of Tk@M1 attributed to the increased O2 from catalase catalyzed decomposition of augmented H2O2, providing a novel idea about constructing natural systems for effective tumor treatment. [ABSTRACT FROM AUTHOR]

Ferredoxin:NADP-oxidoreductase (FNR) catalyzes the reversible exchange of electrons between ferredoxin (Fd) and NADP(H). Reduction of NADP+ by Fd via FNR is essential in the terminal steps of photosynthetic electron transfer, as light-activated electron flow produces NADPH for CO2 assimilation. FNR also catalyzes the reverse reaction in photosynthetic organisms, transferring electrons from NADPH to Fd, which is important in cyanobacteria for respiration and cyclic electron flow (CEF). The cyanobacterium Synechocystis sp. PCC6803 possesses two isoforms of FNR, a large form attached to the phycobilisome (FNRL) and a small form that is soluble (FNRS). While both isoforms are capable of NADPH oxidation or NADP+ reduction, FNRL is most abundant during typical growth conditions, whereas FNRS accumulates under stressful conditions that require enhanced CEF. Because CEF-driven proton pumping in the light–dark transition is due to NDH-1 complex activity and they are powered by reduced Fd, CEF-driven proton pumping and the redox state of the PQ and NADP(H) pools were investigated in mutants possessing either FNRL or FNRS. We found that the FNRS isoform facilitates proton pumping in the dark–light transition, contributing more to CEF than FNRL. FNRL is capable of providing reducing power for CEF-driven proton pumping, but only after an adaptation period to illumination. The results support that FNRS is indeed associated with increased cyclic electron flow and proton pumping, which is consistent with the idea that stress conditions create a higher demand for ATP relative to NADPH. [ABSTRACT FROM AUTHOR]

Main conclusion: Plastoglobules are ubiquitous under non-stress conditions and their morphology, closely related to their composition, changes differently depending on the specific stress that the plant undergoes. Plastoglobules are lipoprotein structures attached to thylakoid membranes, which participate in chloroplast metabolism and stress responses. Their structure contains a coating lipid monolayer and a hydrophobic core that differ in composition. Their function in chloroplasts has been studied focussing on their composition. However, we currently lack a comprehensive study that quantitatively evaluates the occurrence and morphology of plastoglobules. Following a literature search strategy, we quantified the main morphological attributes of plastoglobules from photosynthetic chloroplasts of more than 1000 TEM images published over the last 53 years, covering more than 100 taxa and 15 stress types. The analysis shows that plastoglobules under non-stress conditions are spherical, with an average diameter of 100–200 nm and cover less than 3% of the chloroplast cross-section area. This percentage rises under almost every type of stress, particularly in senescence. Interestingly, an apparent trade-off between increasing either the number or the diameter of plastoglobules governs this response. Our results show that plastoglobules are ubiquitous in chloroplasts of higher plants under non-stress conditions. Besides, provided the specific molecular composition of the core and coat of plastoglobules, we conclude that specific stress-related variation in plastoglobules attributes may allow inferring precise responses of the chloroplast metabolism. [ABSTRACT FROM AUTHOR]

Abstract Background There is a promising outlook regarding the potential effect of spinach-derived thylakoids in the management of obesity and its associated metabolic disturbances. This research aimed to evaluate the effects of spinach-derived thylakoids supplementation combined with a calorie-restricted diet on anthropometric and metabolic profiles in obese women with the polycystic ovary syndrome (PCOS). Methods In a 12-week double-blind placebo-controlled randomized clinical trial, 48 females with obesity and PCOS were randomly allocated into either intervention (5 g/day thylakoid) or placebo (5 g/day cornstarch) groups along with calorie-restricted diets. Anthropometric measures, physical activity levels, dietary intakes, insulin resistance markers, as well as serum levels of insulin, fasting blood glucose (FBG), non-esterified fatty acids (NEFA), and sex hormones including dehydroepiandrosterone sulfate (DHEAS), follicle-stimulating hormone (FSH), luteinizing hormone (LH), sex hormone-binding globulin (SHBG), and free androgen index (FAI) were evaluated pre-and post-intervention. Results After the 12-week intervention, there were significant decreases in weight (− 6.97 ± 0.52 vs. -3.19 ± 0.72 kg; P

Photosynthetic capacity is usually affected by light intensity in the field. In this study, photosynthetic characteristics of four different Triticeae crops (wheat, triticale, barley, and highland barley) were investigated based on chlorophyll fluorescence and the level of photosynthetic proteins under high light. Compared with wheat, three cereals (triticale, barley, and highland barley) presented higher photochemical efficiency and heat dissipation under normal light and high light for 3 h, especially highland barley. In contrast, lower photoinhibition was observed in barley and highland barley relative to wheat and triticale. In addition, barley and highland barley showed a lower decline in D1 and higher increase in Lhcb6 than wheat and triticale under high light. Furthermore, compared with the control, the results obtained from PSII protein phosphorylation showed that the phosphorylation level of PSII reaction center proteins (D1 and D2) was higher in barley and highland barley than that of wheat and triticale. Therefore, we speculated that highland barley can effectively alleviate photodamages to photosynthetic apparatus by high photoprotective dissipation, strong phosphorylation of PSII reaction center proteins, and rapid PSII repair cycle under high light.

There is a surprisingly high morphological similarity between multilamellar concentric thylakoids in cyanobacteria and the myelin sheath that wraps the nerve axons. Thylakoids are multilamellar structures, which express photosystems I and II, cytochromes and ATP synthase necessary for the light-dependent reaction of photosynthesis. Myelin is a multilamellar structure that surrounds many axons in the nervous system and has long been believed to act simply as an insulator. However, it has been shown that myelin has a trophic role, conveying nutrients to the axons and producing ATP through oxidative phosphorylation. Therefore, it is tempting to presume that both membranous structures, although distant in the evolution tree, share not only a morphological but also a functional similarity, acting in feeding ATP synthesized by the ATP synthase to the centre of the multilamellar structure. Therefore, both molecular structures may represent a convergent evolution of life on Earth to fulfill fundamentally similar functions.

The absorbance shift of pigments is proportional to the membrane potential (Δψ) in plants, green algae, and many photosynthetic bacteria. It is currently denoted as ElectroChromic Shift (ECS) at 515–520 nm for plant carotenoids. It is increasingly being used for phenotyping plants for traits related to photosynthesis or chloroplast metabolism because it is a non-invasive technique and also because more instruments are now commercially available from various manufacturers. The ECS technique is currently used to monitor the post-illumination decay of the proton-motive force (pmf), but it has a more general use for quantitative studies on photosynthetic energy transduction. Here we briefly summarize the basic knowledge on ECS, emphasize the full potential of this technique, and propose a quantitative analysis of the photosynthetic performance with the definition of a transmission coefficient for electrons along the photosynthetic chain. [ABSTRACT FROM AUTHOR]

Chloroplast function is orchestrated by the organelle's intricate architecture. By combining cryo-focused ion beam milling of vitreous Chlamydomonas cells with cryo-electron tomography, we acquired three-dimensional structures of the chloroplast in its native state within the cell. Chloroplast envelope inner membrane invaginations were frequently found in close association with thylakoid tips, and the tips of multiple thylakoid stacks converged at dynamic sites on the chloroplast envelope, implicating lipid transport in thylakoid biogenesis. Subtomogram averaging and nearest neighbor analysis revealed that RuBisCO complexes were hexagonally packed within the pyrenoid, with ~15 nm between their centers. Thylakoid stacks and the pyrenoid were connected by cylindrical pyrenoid tubules, physically bridging the sites of light-dependent photosynthesis and light-independent carbon fixation. Multiple parallel minitubules were bundled within each pyrenoid tubule, possibly serving as conduits for the targeted one-dimensional diffusion of small molecules such as ATP and sugars between the chloroplast stroma and the pyrenoid matrix.

Salinity is one of the major problems facing crops worldwide. Salinity can severely affect plants in a negative manner. This study aimed to evaluate the impact of NaCl on morpho– physiological, biochemical, structural and ultrastructural properties in Solanum melongena seedlings under different NaCl concentrations. Plants treated with high concentrations of NaCl showed a nonsignificant decrease in shoot height compared to the controls. However, NaCl concentration of 50 mM and above significantly decreased leaf area, while 75 mM and above significantly reduced the photosynthetic rate (PN) and leaf total sugar content when compared with plants treated with less-concentrated NaCl and the controls. Thick root sections from plants grown in 100 and 150 mM NaCl exhibit severe deformation in the epidermal and cortical layers. Additionally, TEM micrographs of plants treated with 75, 100, and 150 mM exhibited bulgy chloroplasts with loss of integrity thylakoid membranes associated with large starch grains. The changes in plant ultrastructure observed in this study broaden our knowledge about the impact of salinity at the cellular level. [ABSTRACT FROM AUTHOR]

The light-sensitive (LS) albino tea plant grows albinic shoots lacking chlorophylls (Chls) under high-light (HL) conditions, and the albinic shoots re-green under low light (LL) conditions. The albinic shoots contain a high level of amino acids and are preferential materials for processing quality green tea. The young plants of the albino tea cultivars are difficult to be cultivated owing to lacking Chls. The mechanisms of the tea leaf bleaching and re-greening are unknown. We detected the activity and composition of photosystem II (PSII) subunits in LS albino tea cultivar “Huangjinya” (HJY), with a normal green-leaf cultivar “Jinxuan” (JX) as control so as to find the relationship of PSII impairment to the albino phenotype in tea. The PSII of HJY is more vulnerable to HL-stress than JX. HL-induced degradation of PSII subunits CP43, CP47, PsbP, PsbR. and light-harvest chlorophyll–protein complexes led to the exposure and degradation of D1 and D2, in which partial fragments of the degraded subunits were crosslinked to form larger aggregates. Two copies of subunits PsbO, psbN, and Lhcb1 were expressed in response to HL stress. The cDNA sequencing of CP43 shows that there is no difference in sequences of PsbC cDNA and putative amino acids of CP43 between HJY and JX. The de novo synthesis and/or repair of PSII subunits is considered to be involved in the impairment of PSII complexes, and the latter played a predominant role in the albino phenotype in the LS albino tea plant.

Symbiotic relationships are very important for corals. Abiotic stressors cause the acclimatization of cell membranes in symbionts, which possess different membrane acclimatization strategies. Membrane stability is determined by a unique lipid composition and, thus, the profile of thylakoid lipids can depend on coral symbiont species. We have analyzed and compared thylakoid lipidomes (mono- and digalactosyldiacylglycerols (MGDG and DGDG), sulfoquinovosyldiacylglycerols (SQDG), and phosphatidylglycerols (PG)) of crude extracts from symbiotic reef-building coral Acropora sp., the hydrocoral Millepora platyphylla, and the octocoral Sinularia flexibilis. S. flexibilis crude extracts were characterized by a very high SQDG/PG ratio, a DGDG/MGDG ratio < 1, a lower degree of galactolipid unsaturation, a higher content of SQDG with polyunsaturated fatty acids, and a thinner thylakoid membrane which may be explained by the presence of thermosensitive dinoflagellates Cladocopium C3. In contrast, crude extracts of M. platyphylla and Acropora sp. exhibited the lipidome features of thermotolerant Symbiodiniaceae. M. platyphylla and Acropora sp. colonies contained Cladocopium C3u and Cladocopium C71/C71a symbionts, respectively, and their lipidome profiles showed features that indicate thermotolerance. We suggest that an association with symbionts that exhibit the thermotolerant thylakoid lipidome features, combined with a high Symbiodiniaceae diversity, may facilitate further acclimatization/adaptation of M. platyphylla and Acropora sp. holobionts in the South China Sea.

During photosynthesis, electron transport is necessary for carbon assimilation and must be regulated to minimize free radical damage. There is a longstanding controversy over the role of a critical enzyme in this process (ferredoxin:NADP(H) oxidoreductase, or FNR), and in particular its location within chloroplasts. Here we use immunogold labelling to prove that FNR previously assigned as soluble is in fact membrane associated. We combined this technique with a genetic approach in the model plant Arabidopsis to show that the distribution of this enzyme between different membrane regions depends on its interaction with specific tether proteins. We further demonstrate a correlation between the interaction of FNR with different proteins and the activity of alternative photosynthetic electron transport pathways. This supports a role for FNR location in regulating photosynthetic electron flow during the transition from dark to light.