Biology subjects

Perin, G.

Publications and source records attributed to Perin, G..

7 recordsLinked to original sources

bioRxiv2025

Thylakoids reorganization enables driving photosynthesis under far-red light in the microalga Nannochloropsis gaditana

O_LIOxygenic photosynthesis is driven by visible light in most photosynthetic organisms, with exceptions in few cyanobacteria and microalgae species, that can extend the light absorption to far-red wavelengths, by synthesizing new pigments or shifting the antennae absorption range beyond 700 nm. C_LIO_LIIn this work, we describe a novel mechanism of acclimation in the marine microalga Nannochloropsis gaditana, that resulted capable of growth relying solely on far-red light. Unexpectedly, the response did not involve the synthesis of red-shifted absorption forms, rather a peculiar reorganization of chloroplasts. C_LIO_LIThe abundance of photosynthetic complexes changed, with an increased accumulation of all pigment binding proteins and photosystem II. Chloroplasts became bigger and thylakoid membranes increased in number occupying almost all the organelle volume, showing also newly observed structures, composed of a central superstack with perpendicular electrondense interconnections, that we propose to name thylakoidal bodies. C_LIO_LITo the best of our knowledge, these results describe a novel acclimation strategy to far-red light, overall highlighting that the biodiversity of responses to far-red light is currently underestimated. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=174 SRC="FIGDIR/small/665317v1_ufig1.gif" ALT="Figure 1"> View larger version (60K): org.highwire.dtl.DTLVardef@6d9038org.highwire.dtl.DTLVardef@1178b53org.highwire.dtl.DTLVardef@bc0e4corg.highwire.dtl.DTLVardef@4eb999_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗

bioRxiv2025

Photosynthesis regulation impacts carbon and nitrogen assimilation in the diazotrophic cyanobacterium Anabaena sp. PCC 7120

O_LIDiazotrophic cyanobacteria fix both atmospheric carbon (C) and nitrogen (N) into biomass, but the two assimilation pathways are not compatible. Species like Anabaena sp. PCC 7120 physically separates C and N assimilation in different cell types. Even if separated, they are strongly intertwined, as N assimilation relies on the C skeletons and reducing power from photosynthesis, that in turn depends on N rich molecules as pigments and proteins. C_LIO_LIWhereas the two pathways have been extensively studied individually, here we investigate their interaction by analysing photosynthetic properties upon exposure to changes in light, CO2 and N availability, including the contribution of photosynthetic electron fluxes. C_LIO_LIGrowth depended on the availability of both light and CO2, while the N2 fixation activity mainly on the C supply. Upon diazotrophic conditions, the total photosynthetic electron transport activity increased, with a modified contribution of different electron pathways. A mutant strain affected in the vehiculation of fixed N between cell types showed that the modulation of photosynthesis depended on the metabolic connection between assimilation pathways. C_LIO_LIOverall, data showed that the regulation of photosynthetic electron fluxes is a major component of the synergic metabolic relationship between C and N assimilation pathways upon dynamic environmental conditions. C_LI

plant biology↗

bioRxiv2024

The Xanthophyll Cycle balances Photoprotection and Efficiency in the seawater alga Nannochloropsis oceanica

Photosynthetic reactions require continuous modulation to respond to highly dynamic environmental conditions. Regulation of photosynthesis involves various mechanisms, which differ across phylogenetic groups. One such mechanism, found widespread in photosynthetic eukaryotes, is the xanthophyll cycle, which involves the reversible light-dependent conversion between the carotenoids violaxanthin, antheraxanthin, and zeaxanthin. In this study, we investigated the impact of the xanthophyll cycle in Nannochloropsis oceanica, a seawater microalga member of Eustigmatophyta that features a peculiarly high content of xanthophylls. We generated and characterized lines with increased levels of the enzymes involved in the xanthophyll cycle, i.e. violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP) and demonstrated that their content is a main factor in controlling the overall reaction rates and the dynamics of the xanthophyll cycle. Subsequent differences in the xanthophyll profile affect the activation of photoprotection mechanisms such as non-photochemical quenching and tolerance to reactive oxygen species. Interestingly, overexpression of VDE expands the limits of high light tolerance, whereas the increased content of ZEP facilitates faster recovery after exposure to light but also heightened photosensitivity under some conditions. These findings underscore the critical role of the xanthophyll cycle in the regulation of photosynthesis in Nannochloropsis, where it is not simply a mechanism to respond to excess illumination, but plays a central role in modulating photosynthesis, fulfilling the complex task of balancing photoprotection and light-use efficiency under different environmental conditions.

plant biology↗

bioRxiv2023

Assessment of photosynthetic activity in dense microalgae cultures using oxygen production

Microalgae are photosynthetic microorganisms playing a pivotal role in primary production in aquatic ecosystems, sustaining the entry of carbon in the biosphere. Microalgae have also been recognized as sustainable source of biomass to complement crops. For this objective they are cultivated in photobioreactors or ponds at high cell density to maximize biomass productivity and lower the cost of downstream processes. Photosynthesis depends on light availability, that is often not constant over time. In nature, sunlight fluctuates over diurnal cycles and weather conditions. In high-density microalgae cultures of photobioreactors outdoors, on top of natural variations, microalgae are subjected to further complexity in light exposure. Because of the high-density cells experience self-shading effects that heavily limit light availability in most of the mass culture volume. This limitation strongly affects biomass productivity of industrial microalgae cultivation plants with important implication on economic feasibility. Understanding how photosynthesis responds to cell density is informative to assess functionality in the inhomogeneous light environment of industrial photobioreactors. In this work we exploited a high-sensitivity Clark electrode to measure microalgae photosynthesis and compare cultures with different densities, using Nannochloropsis as model organism. We observed that cell density has a substantial impact on photosynthetic activity, and demonstrated the reduction of the cells light-absorption capacity by genetic modification is a valuable strategy to increase photosynthetic functionality of dense microalgae cultures. HighlightsO_LIMicroalgae biomass is a promising alternative to crops. C_LIO_LIThe impact of cultivation at scale on photosynthesis is still under-investigated. C_LIO_LIThe Photosynthesis-Irradiance (PI) relationship is informative. C_LIO_LIHigh-sensitivity oxygen measurements for PI investigation was validated. C_LIO_LIThe effect of cell density on PI was studied in Nannochloropsis pale mutants. C_LI

plant biology↗

bioRxiv2022

Modulation of xanthophyll cycle impacts biomass productivity in the marine microalga Nannochloropsis

Life on earth depends on photosynthetic primary producers that exploit sunlight to fix CO2 into biomass. Approximately half of global primary production is associated with microalgae living in aquatic environments. Microalgae also represent a promising source of biomass to complement crop cultivation, and they could contribute to the development of a more sustainable bioeconomy. Photosynthetic organisms evolved multiple mechanisms involved in the regulation of photosynthesis to respond to highly variable environmental conditions. While essential to avoid photodamage, regulation of photosynthesis results in dissipation of absorbed light energy, generating a complex trade-off between protection from stress and light-use efficiency. This work investigates the impact of the xanthophyll cycle, the light-induced reversible conversion of violaxanthin into zeaxanthin, on the protection from excess light and on biomass productivity in the marine microalgae of the genus Nannochloropsis. Zeaxanthin is shown to have an essential role in protection from excess light, contributing to the induction of Non-Photochemical Quenching and scavenging of reactive oxygen species. On the other hand, the overexpression of Zeaxanthin Epoxidase, enables a faster re-conversion of zeaxanthin to violaxanthin that is shown to be advantageous for biomass productivity in dense cultures in photobioreactors. These results demonstrate that zeaxanthin accumulation is critical to respond to strong illumination, but it may lead to unnecessary energy losses in light-limiting conditions, and accelerating its re-conversion to violaxanthin provides an advantage for biomass productivity in microalgae. Significance StatementThis work investigates the impact of the xanthophyll cycle in marine microalgae on the trade-off between photoprotection and light-use efficiency. Our results demonstrate that whilst zeaxanthin is essential for photoprotection upon exposure to strong illumination, it leads to unnecessary energy losses in light-limiting conditions and thus accelerating its re-conversion to violaxanthin provides an advantage for biomass productivity in microalgae.

plant biology↗

bioRxiv2020

Calm on the surface, dynamic on the inside. Molecular homeostasis in response to regulatory and metabolic perturbation of Anabaena sp. 7120 nitrogen metabolism

Nitrogen is a key macro-nutrient required for the metabolism and growth of biological systems. Although multiple nitrogen sources can serve this purpose, they are all converted into ammonium/ammonia as a first step of assimilation. It is thus reasonable to expect that molecular parts involved in the transport of ammonium/ammonia across biological membranes (i.e. catalysed by AMT transporters) connect with the regulation of both nitrogen and central carbon metabolism. In order to test this hypothesis, we applied both (1) genetic (i.e. {Delta}amt mutation) and (2) environmental treatments to a target biological system, the cyanobacterium Anabaena sp. PCC 7120. Cyanobacteria have a key role in the global nitrogen cycle and thus represent a useful model system. The aim was to both (1) perturb sensing and low-affinity uptake of ammonium/ammonia and (2) induce multiple inner N states, followed by targeted quantification of key proteins, metabolites and enzyme activities, with experiments intentionally designed over a longer time-scale than the available studies in literature. We observed that the absence of AMT transporters triggered a substantial response at a whole-system level, affecting enzyme activities and the quantity of both proteins and metabolites, spanning both N and C metabolism. Moreover, the absence of AMT transporters left a molecular fingerprint indicating N-deficiency even under N replete conditions (i.e. greater GS activity, lower 2-OG content and faster nitrogenase activation upon N deprivation). Contrasting with all of the above dynamic adaptations was the striking near-complete lack of any externally measurable phenotype (i.e. growth, photosynthesis, pigments, metabolites). We thus conclude that this species evolved a highly robust and adaptable molecular network to maintain homeostasis, resulting in substantial internal but minimal external perturbations. The analytical data highlights several internal adaptations, including increased N assimilation (i.e. greater GS activity) and nitrogenase activity (i.e. faster activation upon N deprivation) together with altered amino acids metabolism, as indicated by changes in Gln, Glu and 2-OG, indicating an altered C/N balance. The analyses provides evidence for an active role of AMT transporters in the regulatory/signalling network of N metabolism in this biological system, and the existence of a novel fourth IF7A-independent regulatory mechanism controlling GS activity.

systems biology↗

bioRxiv2018

Conformational dynamics of a photosynthetic light-harvesting complex in native thylakoid membranes

Photosynthetic light-harvesting complexes of higher plants, moss and green algae can undergo dynamic conformational transitions, which have been correlated to their ability to adapt to fluctuations in the light environment. Herein, we demonstrate the application of solid-state NMR spectroscopy on native, heterogeneous thylakoid membranes of Chlamydomonas reinhardtii (Cr) and on Cr Light-Harvesting Complex II (LHCII) in thylakoid lipid bilayers to detect LHCII conformational dynamics in its native membrane environment. We show that membrane-reconstituted LHCII contains selective sites that undergo fast, large-amplitude motions, including the phytol tails of two chlorophylls. Protein plasticity is also observed in the N-terminal stromal loop and in protein fragments facing the lumen, involving sites that stabilize the xanthophyll-cycle carotenoid violaxanthin and the two luteins. The results report on the intrinsic flexibility of LHCII pigment-protein complexes in a membrane environment, revealing putative sites for conformational switching. In thylakoid membranes, fast dynamics of protein and pigment sites is significantly reduced, which suggests that in their native organelle membranes, LHCII complexes are locked in specific conformational states. STATEMENT OF SIGNIFICANCEPhotosynthetic Light-Harvesting Complexes undergo dynamic conformational transitions that regulate the capacity of the light-harvesting antenna. We demonstrate the application of solid-state (ss)NMR spectroscopy to investigate the structural dynamics of LHCII, the most abundant LHC complex of plants and algae, in native membranes. Selective dynamic protein and pigment residues are identified that are putative sites for a conformational switch.

biophysics↗