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Diatoms are a group of silicified algae that play a major role in marine and freshwater ecosystems. Diatom chloroplasts were acquired by secondary endosymbiosis and exhibit important structural and functional differences from the primary plastids of land plants and green algae. Many functions of primary plastids, including photoacclimation and inorganic carbon acquisition, are regulated by calcium-dependent signaling processes. Calcium signaling has also been implicated in the photoprotective responses of diatoms; however, the nature of calcium elevations in diatom chloroplasts and their wider role in cell signaling remains unknown. Using genetically encoded calcium indicators, we find that the diatom Phaeodactylum tricornutum exhibits dynamic calcium elevations within the chloroplast stroma. Stromal calcium ([Ca2+]str) acts independently from the cytosol and is not elevated by stimuli that induce large cytosolic calcium ([Ca2+]cyt) elevations. In contrast, high light and exogenous hydrogen peroxide (H2O2) induce large, sustained [Ca2+]str elevations that are not replicated in the cytosol. Measurements using the fluorescent H2O2 sensor roGFP2-Oxidant Receptor Peroxidase 1 (Orp1) indicate that [Ca2+]str elevations induced by these stimuli correspond to the accumulation of H2O2 in the chloroplast. [Ca2+]str elevations were also induced by adding methyl viologen, which generates superoxide within the chloroplast, and by treatments that disrupt nonphotochemical quenching (NPQ). The findings indicate that diatoms generate specific [Ca2+]str elevations in response to high light and oxidative stress that likely modulate the activity of calcium-sensitive components in photoprotection and other regulatory pathways., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Pyrenoids are subcompartments of algal chloroplasts that increase the efficiency of Rubisco-driven CO 2 fixation. Diatoms fix up to 20% of global CO 2 , but their pyrenoids remain poorly characterized. Here, we used in vivo photo-crosslinking to identify pyrenoid shell (PyShell) proteins, which we localized to the pyrenoid periphery of model pennate and centric diatoms, Phaeodactylum tricornutum and Thalassiosira pseudonana. In situ cryo-electron tomography revealed that pyrenoids of both diatom species are encased in a lattice-like protein sheath. Single-particle cryo-EM yielded a 2.4-Å-resolution structure of an in vitro TpPyShell1 lattice, which showed how protein subunits interlock. T. pseudonana TpPyShell1/2 knockout mutants had no PyShell sheath, altered pyrenoid morphology, and a high-CO 2 requiring phenotype, with reduced photosynthetic efficiency and impaired growth under standard atmospheric conditions. The structure and function of the diatom PyShell provide a molecular view of how CO 2 is assimilated in the ocean, a critical ecosystem undergoing rapid change., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Photosynthetic algae have evolved mechanisms to cope with suboptimal light and CO 2 conditions. When light energy exceeds CO 2 fixation capacity, Chlamydomonas reinhardtii activates photoprotection, mediated by LHCSR1/3 and PSBS, and the CO 2 Concentrating Mechanism (CCM). How light and CO 2 signals converge to regulate these processes remains unclear. Here, we show that excess light activates photoprotection- and CCM-related genes by altering intracellular CO 2 concentrations and that depletion of CO 2 drives these responses, even in total darkness. High CO 2 levels, derived from respiration or impaired photosynthetic fixation, repress LHCSR3/CCM genes while stabilizing the LHCSR1 protein. Finally, we show that the CCM regulator CIA5 also regulates photoprotection, controlling LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 protein accumulation. This work has allowed us to dissect the effect of CO 2 and light on CCM and photoprotection, demonstrating that light often indirectly affects these processes by impacting intracellular CO 2 levels., (© 2023. The Author(s).)

Eukaryotic phytoplankton have a small global biomass but play major roles in primary production and climate. Despite improved understanding of phytoplankton diversity and evolution, we largely ignore the cellular bases of their environmental plasticity. By comparative 3D morphometric analysis across seven distant phytoplankton taxa, we observe constant volume occupancy by the main organelles and preserved volumetric ratios between plastids and mitochondria. We hypothesise that phytoplankton subcellular topology is modulated by energy-management constraints. Consistent with this, shifting the diatom Phaeodactylum from low to high light enhances photosynthesis and respiration, increases cell-volume occupancy by mitochondria and the plastid CO 2 -fixing pyrenoid, and boosts plastid-mitochondria contacts. Changes in organelle architectures and interactions also accompany Nannochloropsis acclimation to different trophic lifestyles, along with respiratory and photosynthetic responses. By revealing evolutionarily-conserved topologies of energy-managing organelles, and their role in phytoplankton acclimation, this work deciphers phytoplankton responses at subcellular scales.

Background: Few studies on the relationship between sleep quantity and/or quality and cognition have been conducted among preschoolers from the healthy general population. We aimed to identify, among 3-year-old children, early polysomnography (PSG) sleep factors associated with estimated intelligence quotient (IQ) using the Weschler Preschool and Primary Scale Intelligence-III test (WPPSI-III) and its indicators: full-scale (FISQ), verbal (VIQ), and performance (PIQ) intelligence quotients., Methods: We included full-term children from the French birth-cohort AuBE with PSG recording at term (M0) and/or six months (M6), and available WPPSI-III scores at three years. Sleep and arousal characteristics of these infants were evaluated during day and night sleep periods. Relationships between IQ scores and sleep parameters were estimated using models with the child as a repeated effect adjusted for time (night/day), maturation (M0/M6), tobacco exposure (yes/no), anxiety-depressive scores during pregnancy, maternal age, duration of breastfeeding and child's gender., Results: A total of 118 PSG recordings were obtained, representing a total of 78 unique children (38 with one PSG and 40 with two PSG). No correlations were found between night and day sleep durations at M0 or M6. Mean VIQ, PIQ, and FSIQ scores were within normal ranges. In multivariate models, longer sleep duration and higher sleep efficiency during the day were negatively associated with all IQ scores. More frequent arousals during the night were associated with lower VIQ scores., Conclusion: Early sleep characteristics such as night sleep fragmentation or longer naps could be associated with impaired cognitive function at three years of age., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: While heart rate variability (HRV) constitutes a relevant non-invasive tool to assess the autonomic nervous system (ANS) function with recognized diagnostic or therapeutic implications, there is still a lack of established data on maturation of autonomic control of heart rate during the first months of life. The Autonomic Baby Evaluation ( AuBE ) cohort was built to establish, the normal autonomic maturation profile from birth up to 2 years, in a healthy population of full-term newborns., Methods: Heart rate variability analysis was carried out in 271 full-term newborns (mean gestational age 39 wGA + 5 days) from reliable polysomnographic recordings at 0 (n = 270) and 6 (n = 221) months and from a 24-hour ambulatory electrocardiogram (ECG) at 12 (n = 210), 18 (n = 197), and 24 (n = 190) months. Indices of HRV analysis were calculated through the ANSLabTools software., Results: Indices are dissociated according a temporal, geometrical, frequency, Poincaré, empirical mode decomposition, fractal, Chaos and DC/AC and entropy analysis. Each index is presented for five different periods of time, 0, 6, 12, 18 and 24 months and with smoothed values in the 3rd, 10th, 50th, 90th and 97th percentiles. Data are also presented for the full cohort and individualized by sex to account for gender variability., Discussion & Conclusion: The physiological autonomic maturation profile from birth to 2 years in a healthy population of term neonates results in a fine-tuning autonomic maturation underlying progressively a new equilibrium and privileging the parasympathetic activity over the sympathetic activity.

The so-called "complex" plastids from diatoms possessing four envelope membranes are a typical feature of algae that arose from secondary endosymbiosis. Studying isolated plastids from these algae may allow answering a number of fundamental questions regarding diatom photosynthesis and plastid functionality. Due to their complex architecture and their integration into the cellular endoplasmic reticulum (ER) system, their isolation though is still challenging. In this work, we report a reliable isolation technique that is applicable for the two model diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum. The resulting plastid-enriched fractions are of homogenous quality, almost free from cellular contaminants, and feature structurally intact thylakoids that are capable to perform oxygenic photosynthesis, though in most cases they seem to lack most of the stromal components as well as plastid envelopes.

Internal chloroplast structures present complex and various characteristics, which are still largely undetermined due to insufficient imaging investigation. Information on chloroplast morphology has traditionally been collected using light microscopy (LM), confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques. However, recent technological progresses in the field of microscopy have made it possible to visualize the internal structure of chloroplast in far greater detail and in 3D. Here we recapitulate protocols to visualize chloroplasts from Arabidopsis leaves and Phaeodactylum tricornutum cells with confocal and transmission electron microscopy together with a new technique using a focused ion beam-scanning electron microscope (FIB-SEM) allowing for 3D imaging.

Photosynthesis is a unique process that allows independent colonization of the land by plants and of the oceans by phytoplankton. Although the photosynthesis process is well understood in plants, we are still unlocking the mechanisms evolved by phytoplankton to achieve extremely efficient photosynthesis. Here, we combine biochemical, structural and in vivo physiological studies to unravel the structure of the plastid in diatoms, prominent marine eukaryotes. Biochemical and immunolocalization analyses reveal segregation of photosynthetic complexes in the loosely stacked thylakoid membranes typical of diatoms. Separation of photosystems within subdomains minimizes their physical contacts, as required for improved light utilization. Chloroplast 3D reconstruction and in vivo spectroscopy show that these subdomains are interconnected, ensuring fast equilibration of electron carriers for efficient optimum photosynthesis. Thus, diatoms and plants have converged towards a similar functional distribution of the photosystems although via different thylakoid architectures, which likely evolved independently in the land and the ocean.

The ability of phototrophs to colonise different environments relies on robust protection against oxidative stress, a critical requirement for the successful evolutionary transition from water to land. Photosynthetic organisms have developed numerous strategies to adapt their photosynthetic apparatus to changing light conditions in order to optimise their photosynthetic yield, which is crucial for life on Earth to exist. Photosynthetic acclimation is an excellent example of the complexity of biological systems, where highly diverse processes, ranging from electron excitation over protein protonation to enzymatic processes coupling ion gradients with biosynthetic activity, interact on drastically different timescales from picoseconds to hours. Efficient functioning of the photosynthetic apparatus and its protection is paramount for efficient downstream processes, including metabolism and growth. Modern experimental techniques can be successfully integrated with theoretical and mathematical models to promote our understanding of underlying mechanisms and principles. This review aims to provide a retrospective analysis of multidisciplinary photosynthetic acclimation research carried out by members of the Marie Curie Initial Training Project, AccliPhot, placing the results in a wider context. The review also highlights the applicability of photosynthetic organisms for industry, particularly with regards to the cultivation of microalgae. It intends to demonstrate how theoretical concepts can successfully complement experimental studies broadening our knowledge of common principles in acclimation processes in photosynthetic organisms, as well as in the field of applied microalgal biotechnology., (© The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Objectives Sleep problems and deprivation are common during pregnancy, particularly in the third trimester. Previous studies are mostly descriptive or focused on specific clinical groups and late pregnancy. We aimed to identify sleep duration trajectories during the pregnancy period, their associated factors, and impact on pregnancy and birth outcomes. Methods We studied 200 women from a mother-child cohort recruited in 2009-2011 from the French general population. We used semi-parametric models to analyze data collected through questionnaires. Results We detected three sleep duration trajectories during pregnancy: short-decreasing (<6.5h/night, 10.8% of the sample), medium-decreasing (6.5-8h/night, 57.6%), and long-increasing (>8h/night, 31.6%) trajectories. Factors associated with the short-decreasing trajectory relative to the medium-decreasing trajectory were older age (odds-ratio/year = 1.13 [95%Confidence-Interval 1.00-1.29]) and working > 28 weeks of gestational age (odds-ratio = 0.30 [0.10-0.90]). Sleep duration during pregnancy in this trajectory group was modified by insomniac symptoms (regression coefficient/trimester = -0.74 [Standard-Error 0.12]) and naps (regression coefficient/trimester = 0.58 [0.25]). Restless legs syndrome was the only factor associated with the long-increasing trajectory and decreased sleep duration (regression coefficient/trimester = -0.88 [0.25]). Assisted delivery (i.e. cesarean section and/or instrumental delivery) and post-partum depression were more frequent among women with the short-decreasing and long-increasing trajectories whereas cesarean section alone was more prevalent among those with the short-decreasing trajectory. Proportion of premature births was higher in the short-decreasing trajectory group. Birth-weight-z-score was lower in the long-increasing trajectory group. Conclusion We identified sleep trajectories among pregnant women with specific risk factors that could affect both pregnancy and birth outcomes. Taking these into consideration could improve both maternal and child health.

Objective: This study investigated sleep architecture in newborn and six-month-old infants who were born to depressed mothers., Method: Sixty-four healthy full-term infants (32 males and 32 females) participated in the study. Of these, 32 were high-risk infants who were born to mothers diagnosed with depression, and 32 were low-risk infants born to mothers without a personal history of depression. 24-hour polysomnography was recorded at zero and six months of age (M0 and M6). Sleep macro-structural parameters (total sleep time, TST; awake time; non-rapid eye movement, NREM sleep (%); rapid eye movement, REM sleep %; arousal index; and sleep efficiency) were analysed at M0 and M6. Micro-architectural sleep features (slow-wave activity, SWA; delta sleep ratio, DSR; spindle density; and rapid eye movement density) were calculated at M6. The data between high-risk and low-risk groups were compared using Student's t-tests., Results: At M0 and M6, the high-risk infants showed more awake time and fewer arousals than the low-risk infants. However, the high-risk group had less NREM% at M0 and a shorter TST as well as less REM% at M6 than the low-risk group. At M6, the high-risk group showed higher SWA, higher DSR and lower spindle density in comparison with the low-risk group., Conclusions: Altered sleep structure was observed during their first months of life in infants born from depressed mothers, thereby suggesting that the prenatal environment could enhance the depression vulnerability of the child and potentially decrease their neuroplasticity., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Background: Few studies on the relations between sleep quantity and/or quality and cognition have been conducted among preschoolers from healthy general population. We aimed at identifying, among 36 months old children, early factors associated with intelligence quotient (IQ) estimated through the Weschler Preschool and Primary Scale Intelligence-III test and its indicators: Full-Scale-, Verbal- and Performance-IQs and their subscale scores., Methods: We included 194 children from the French birth cohort AuBE with both available Weschler Preschool and Primary Scale Intelligence-III scores at three years and sleep data. Information was collected through self-questionnaires at birth, 6, 12, 18 and 24 months. A day/night sleep ratio was calculated., Results: Mean scores were in normal ranges for Verbal, Performance, and Full-Scale IQs ?. In multivariate models, being a third-born or more child and watching television ≥1 h/day at 24 months were negatively associated with all IQ scores, whereas collective care arrangement was positively associated. Night waking at six months and frequent snoring at 18 months were negatively associated with Performance IQ, some subscales, and Full Scale IQ contrary to day/night sleep ratio at 12 months. No association was observed between early sleep characteristics and Verbal IQ., Conclusion: We showed that early features including infant sleep characteristics influence IQ scores at 36 months old. Some of these may be accessible to prevention., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In plants and algae, light serves both as the energy source for photosynthesis and a biological signal that triggers cellular responses via specific sensory photoreceptors. Red light is perceived by bilin-containing phytochromes and blue light by the flavin-containing cryptochromes and/or phototropins (PHOTs), the latter containing two photosensory light, oxygen, or voltage (LOV) domains. Photoperception spans several orders of light intensity, ranging from far below the threshold for photosynthesis to values beyond the capacity of photosynthetic CO 2 assimilation. Excess light may cause oxidative damage and cell death, processes prevented by enhanced thermal dissipation via high-energy quenching (qE), a key photoprotective response. Here we show the existence of a molecular link between photoreception, photosynthesis, and photoprotection in the green alga Chlamydomonas reinhardtii. We show that PHOT controls qE by inducing the expression of the qE effector protein LHCSR3 (light-harvesting complex stress-related protein 3) in high light intensities. This control requires blue-light perception by LOV domains on PHOT, LHCSR3 induction through PHOT kinase, and light dissipation in photosystem II via LHCSR3. Mutants deficient in the PHOT gene display severely reduced fitness under excessive light conditions, indicating that the sensing, utilization, and dissipation of light is a concerted process that plays a vital role in microalgal acclimation to environments of variable light intensities.

In oxygenic photosynthesis, light produces ATP plus NADPH via linear electron transfer, i.e. the in-series activity of the two photosystems: PSI and PSII. This process, however, is thought not to be sufficient to provide enough ATP per NADPH for carbon assimilation in the Calvin-Benson-Bassham cycle. Thus, it is assumed that additional ATP can be generated by alternative electron pathways. These circuits produce an electrochemical proton gradient without NADPH synthesis, and, although they often represent a small proportion of the linear electron flow, they could have a huge importance in optimizing CO 2 assimilation. In Viridiplantae, there is a consensus that alternative electron flow comprises cyclic electron flow around PSI and the water to water cycles. The latter processes include photosynthetic O 2 reduction via the Mehler reaction at PSI, the plastoquinone terminal oxidase downstream of PSII, photorespiration (the oxygenase activity of Rubisco) and the export of reducing equivalents towards the mitochondrial oxidases, through the malate shuttle. In this review, we summarize current knowledge about the role of the water to water cycles in photosynthesis, with a special focus on their occurrence and physiological roles in microalgae., (© The Author 2016. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Diatoms contain a secondary plastid that derives from a red algal symbiont. This organelle is limited by four membranes. The two outermost membranes are the chloroplast endoplasmic reticulum membrane (cERM), which is continuous with the host outer nuclear envelope, and the periplastidial membrane (PPM). The two innermost membranes correspond to the outer and inner envelope membranes (oEM and iEM) of the symbiont's chloroplast. Between the PPM and oEM lies a minimized symbiont cytoplasm, the periplastidial compartment (PPC). In Phaeodactylum tricornutum, PPC-resident proteins are localized in "blob-like-structures", which remain associated with plastids after cell disruption. We analyzed disrupted Phaeodactylum cells by focused ion beam scanning electron microscopy, revealing the presence of a vesicular network (VN) in the PPC, at a location consistent with blob-like structures. Presence of a VN in the PPC was confirmed in intact cells. Additionally, direct membrane contacts were observed between the PPM and nuclear inner envelope membrane at the level of the chloroplast-nucleus isthmus. This study provides insights into the PPC ultrastructure and opens perspectives on the function of this residual cytoplasm of red algal origin., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Diatoms are one of the most ecologically successful classes of photosynthetic marine eukaryotes in the contemporary oceans. Over the past 30 million years, they have helped to moderate Earth's climate by absorbing carbon dioxide from the atmosphere, sequestering it via the biological carbon pump and ultimately burying organic carbon in the lithosphere. The proportion of planetary primary production by diatoms in the modern oceans is roughly equivalent to that of terrestrial rainforests. In photosynthesis, the efficient conversion of carbon dioxide into organic matter requires a tight control of the ATP/NADPH ratio which, in other photosynthetic organisms, relies principally on a range of plastid-localized ATP generating processes. Here we show that diatoms regulate ATP/NADPH through extensive energetic exchanges between plastids and mitochondria. This interaction comprises the re-routing of reducing power generated in the plastid towards mitochondria and the import of mitochondrial ATP into the plastid, and is mandatory for optimized carbon fixation and growth. We propose that the process may have contributed to the ecological success of diatoms in the ocean.

Ions play fundamental roles in all living cells and their gradients are often essential to fuel transports, to regulate enzyme activities and to transduce energy within and between cells. Their homeostasis is therefore an essential component of the cell metabolism. Ions must be imported from the extracellular matrix to their final subcellular compartments. Among them, the chloroplast is a particularly interesting example because there, ions not only modulate enzyme activities, but also mediate ATP synthesis and actively participate in the building of the photosynthetic structures by promoting membrane-membrane interaction. In this review, we first provide a comprehensive view of the different machineries involved in ion trafficking and homeostasis in the chloroplast, and then discuss peculiar functions exerted by ions in the frame of photochemical conversion of absorbed light energy., (Copyright © 2014 Elsevier Ltd. All rights reserved.)