Biology subjects

Morosinotto, T.

Publications and source records attributed to Morosinotto, T..

At least 19 recordsLinked to original sources

bioRxiv2026

Evolutionary co-option of the ancient protein AMBRA1 in plant photomorphogenesis

Photomorphogenesis, the light-driven developmental program of plants, is repressed in darkness by the CUL4-DDB1-COP1 ubiquitin ligase complex. In animals, AMBRA1 is a substrate receptor for the same CUL4-DDB1 machinery, regulating proteostasis, cell proliferation and autophagy, but its role in plants has remained unknown. Here we show that the moss Physcomitrium patens carries two light-regulated AMBRA1 genes, AMBRA1a and AMBRA1b, whose loss impairs vegetative growth and cell-fate transitions under light and prevents the elongation of gravitropic filaments in darkness, indicating that AMBRA1 is required to repress photomorphogenesis. AMBRA1 localizes to the nucleus under both long-day and dark conditions, and its loss causes widespread transcriptional reprogramming of developmental and metabolic pathways, including repression of photosynthesis-related genes in darkness. These findings identify AMBRA1 as a previously unrecognized nuclear regulator that links light availability to plant growth and as a key repressor of photomorphogenesis.

plant biology↗

bioRxiv2026

Mapping the pathway for protein secretion in the secondary endosymbiotic alga Nannochloropsis oceanica

Microalgae are key primary producers in marine ecosystems, and their interactions with the surrounding environment rely on the secretion of intracellular metabolites and macromolecules, particularly proteins, supporting essential functions such as nutrient acquisition, environmental sensing and biotic interactions. Most abundant and ecologically relevant seawater algae are secondary endosymbionts, where multiple endosymbiotic events extensively reshaped plastids and intracellular membrane systems, requiring adaptation of protein trafficking mechanisms. This study presents the identification of signal peptides that direct protein secretion in the seawater microalga Nannochloropsis oceanica. Their expression in frame with a fluorescent tag enabled to reconstruct the protein secretion pathway in this organism. Proteins channelled for export are first targeted to the periplastidial compartment, an exclusive structure of secondary endosymbiotic algae, that acts as hub for protein trafficking. Subsequently, vesicle-mediated transport directs proteins through the endoplasmic reticulum into the periplasmic space between the cell membrane and the cell wall, from where they are released upon cell division. These findings reveal an evolutionarily remodeled protein secretion pathway, in which host- and endosymbiont-derived trafficking mechanisms merged into an integrated functional system. Significance StatementThe most abundant and ecologically relevant marine algae are secondary endosymbionts whose evolution required extensive re-adaptation of multiple cellular processes. Among them, protein secretion is essential for the interaction with external environment, and required specific re-shaping to the increased cellular complexity associated with endosymbiosis. This work uncovers protein secretory pathway in the secondary endosymbiont seawater alga Nannochloropsis oceanica showing that is does not follow a direct route, but proteins are first accumulated in the periplastidial compartment, a unique structure derived from its endosymbiotic history, before being directed for secretion. The final pathway integrated components derived from both the host and endosymbiont, highlighting how evolution was able to merge different biological modules to build an integrated and functional system.

plant biology↗

bioRxiv2026

VIA1 is a conserved regulator of thylakoid membrane integrity that acts through VIPP1

Thylakoid membranes are indispensable for oxygenic photosynthesis, yet the mechanisms that protect these membranes from photooxidative damage remain poorly understood. By screening previously uncharacterized proteins induced during the chloroplast unfolded protein response, we identify VIA1 as an essential factor for preserving thylakoid integrity under high light in the model green alga Chlamydomonas reinhardtii. Loss of VIA1 causes hypersensitivity to photo-oxidative stress and rapid thylakoid swelling. VIA1 localizes to thylakoid membranes and directly binds Vesicle-Inducing Protein in Plastids 1 (VIPP1), an ESCRT-III-like protein essential for thylakoid biogenesis and remodeling. Structure-guided mutagenesis shows that this interaction is required for VIA1 function and is mediated by a winged-helix domain interface reminiscent of ESCRT-II/ESCRT-III binding mode. VIA1 orthologs from cyanobacteria and land plants rescue the Chlamydomonas via1 mutant phenotype, and disruption of VIA1 in Synechocystis sp. PCC 6803 impairs growth, especially under light stress. Together, these findings establish VIA1 as an evolutionarily conserved protein that contributes to thylakoid membrane homeostasis via its interaction with VIPP1. Significance StatementFrom cyanobacteria to land plants, all organisms performing oxygenic photosynthesis rely on thylakoid membranes to capture light and and produce oxygen. Yet these membranes are highly susceptible to environmental stress, particularly excess light, which causes oxidative damage to membrane lipids and proteins. How thylakoid integrity is maintained under these conditions remains a key open question. Here we identify VIA1 as a conserved factor required for maintaining thylakoid membrane structure under high light. VIA1 interacts with VIPP1, an ESCRT-III-like protein essential for thylakoid biogenesis, through a functionally indispensable interface reminiscent of ESCRT-II/ESCRT-III binding mode. The conservation of the VIA1-VIPP1 module across photosynthetic prokaryotes and eukaryotes suggests it arose early in the evolution of oxygenic photosynthesis and has been maintained ever since.

cell biology↗

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

Harnessing photosynthetic ATP for whole-cell biocatalysis in the cyanobacterium Synechocystis

Photosynthetic organisms use sunlight to produce ATP and NADPH powering their metabolism. Harnessing these products for driving biocatalytic reactions would enable to develop clean and sustainable alternatives for chemical reactions. In this study, we present the first demonstration that ATP produced from the photosynthetic process, can fuel a biocatalytic transformation in the whole-cell configuration. This result was achieved by expressing in the cyanobacterium Synechocystis sp. PCC 6803 an ATP-dependent enzyme, the {gamma}-Glutamyl-MethylAmide Synthetase from Methylovorus mays No. 9 (MmGMAS). The expressed enzyme was able to drive in the transgenic strain the light-driven biosynthesis of L-theanine. Consumption of ATP by the recombinant MmGMAS was even beneficial under strong illumination, protecting the photosynthetic electron transport from photodamage. These findings demonstrate the possibility of using photosynthetic microorganisms like Synechocystis as potential platform for sunlight driven biotransformations with wide potential biocatalytic applications. In this perspective, we further present the tridimensional structure of MmGMAS, which explains its promiscuous in vivo activity and provides the basis for its rational evolution.

biochemistry↗

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↗

bioRxiv2025

Sequencing a botanical monument: a chromosome-level assembly of the 400-year-old Goethe's Palm (Chamaerops humilis L.) at the Botanical Garden of the University of Padua (Italy)

The rapid decline in global biodiversity highlights the urgent need for conservation efforts, with botanical gardens playing a crucial role in ex situ plant preservation. Monumental plants, such as the 400-year-old Goethes Palm (Chamaerops humilis L.) at the UNESCO Botanical Garden of the University of Padua (Italy), serve as vital flagship species with significant ecological and cultural value. In this study, we present the first high-quality, chromosome-level genome assembly of C. humilis, using PacBio HiFi and Arima Hi-C sequencing technologies. This genome is the most contiguous and complete within the Arecaceae family to date, with an exceptionally high repeat content of 88%, of which 63% is attributed to Long Terminal Repeat (LTR) elements. Comparative analysis of the transposable element (TE) landscape in palms suggests that the LTR expansion in C. humilis is likely the result of recent TE bursts. Furthermore, we provide the first comprehensive annotation of microRNAs (miRNAs) in the Arecaceae family, identifying, for the first time in palms, the miRNA family miR827, which plays a key role in nutrient regulation. Microsatellite analysis suggests that it probably belongs to the Western genetic lineage of C. humilis. These findings represent a significant advancement in the conservation genomics of this species, laying the groundwork for enhanced preservation strategies, with botanical gardens as pivotal actors in the fight to safeguard global biodiversity.

genomics↗

bioRxiv2025

AI-based prediction of herbarium sequencing success across the plant tree of life

DNA recovered from herbarium specimens represents a vital asset in botanical research, playing a pivotal role in unravelling the evolution, diversity, and ecological dynamics of plants. Despite its importance, challenges such as fragmented DNA and insufficient sequencing yields render molecular data retrieval a high-risk and costly endeavour involving the use of non-replaceable herbarium specimens. Here, we propose a framework based on Artificial Intelligence (AI) to forecast the success of genomic DNA extraction suitable for sequencing from herbarium samples. Our model integrates morphological characteristics and sample colour derived from scanned herbarium images, metadata including sample age and locality, and DNA quantity measurements of samples. We train a deep learning algorithm with ca. 2,000 specimens that have been digitized and sequenced in the framework of the Plant and Fungal Trees of Life (PAFTOL) Project, spanning from year 1832 to the present. As training datasets increase with ongoing digitization and genomic sequencing efforts, our AI predictive model can support researchers in selecting the herbarium samples with the highest likelihood of yielding high-quality genomic DNA from amongst a vast array of globally distributed candidate specimens. Our approach enhances the contribution of herbarium-derived DNA in large-scale studies and facilitates the utilisation of historical collections for a deeper understanding of plant evolution and ecology, with implications for conservation.

plant biology↗

bioRxiv2025

Flavodiiron protein activity outcompetes cyclic electron transport when expressed in angiosperm Nicotiana tabacum

In conditions of excess illumination, alternative electron transport pathways in the thylakoid membranes protect the photosynthetic apparatus against damage from eventual over-reduction. Two main pathways downstream of photosystem I (PSI) enable alternative electron flow, mitigating PSI acceptor-side limitation, while contributing to ATP biosynthesis without reducing NADP+ to NADPH: cyclic electron transport (CET) and pseudo-cyclic electron transport (PCET). Flavodiiron proteins (FLV) are crucial enzymes in PCET, found in all photosynthetic organisms but lost during the evolution of angiosperms. The absence of FLV coding sequences in angiosperm genomes raises intriguing questions about their role and function in photosynthetic organisms. Previous studies utilizing heterologous expression have already demonstrated that FLV can function in angiosperms. In this study, Physcomitrium patens FLVA and FLVB coding sequences were stably expressed in wild-type Nicotiana tabacum, a model crop species. Transgenic lines exhibited significantly increased PCET rates, with FLV-dependent electron transport competing for electrons with CET, particularly under sudden increases in light intensity that limited acceptor side limitation. These findings indicate that FLVs are not only active but also play a critical role in protecting from over-reduction the photosynthetic apparatus of Nicotiana tabacum under fluctuating light conditions.

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↗

bioRxiv2024

Inactivation of mitochondrial complex IV in Physcomitrium patens reveals the essential role of respiration in coordinating plants metabolism

Photosynthetic organisms use sunlight as energy source but rely on respiration during the night and in non-photosynthetic tissues. Respiration is also active in photosynthetically active cells, where its role is still unclear due to a lack of viable mutants. Plants lacking cytochrome c oxidase (complex IV) activity are generally lethal but were here isolated exploiting the possibility of generating knockout lines through vegetative propagation in the moss Physcomitrium patens. The mutants showed severely impaired growth, with an altered composition of the respiratory apparatus and increased electron transfer through the alternative oxidase. The light phase of photosynthesis remained largely unaffected while the efficiency of carbon fixation was moderately reduced. Transcriptomic and metabolomic analyses showed that the disruption of the cytochrome pathway had broad consequences for carbon and nitrogen metabolism. A major alteration in nitrogen assimilation was observed with a general reduction in amino acid abundance. A partial rescue of the growth could be obtained by growing the plants with an external supply of amino acids but not with sugars, demonstrating that respiration in plant photosynthetic cells plays an essential role at the interface between carbon and nitrogen metabolism and a key role in providing carbon skeletons for amino acid biosynthesis.

plant biology↗

bioRxiv2024

Physcomitrium patens flavodiiron proteins form a redox-dependent heterocomplex.

Flavodiiron proteins (FLVs) catalyze the reduction of oxygen to water by exploiting electrons from Photosystem I (PSI). In several photosynthetic organisms such as cyanobacteria, green algae, mosses and gymnosperms, FLV-dependent electron flow protects PSI from over-reduction and consequent damage especially under fluctuating light conditions. In this work we investigated biochemical and structural properties of FLVA and FLVB from the model moss Physcomitrium patens. The two proteins, expressed and purified from Escherichia coli, bind both iron and flavin cofactors and show NAD(P)H oxidase activity as well as oxygen reductase capacities. Moreover, the co-expression of both FLVA and FLVB, coupled to a tandem affinity purification procedure with two different affinity tags, enabled the isolation of the stable and catalytically active FLVA/B hetero multimer protein complex, that has never been isolated and characterized so far. The multimeric organization was shown to be stabilized by inter-subunit disulfide bonds. This investigation provides valuable new information on the biochemical properties of FLVs, with new insights into their in vivo role and regulation.

plant biology↗

bioRxiv2024

Mitochondrial respiration is essential for photosynthesis-dependent ATP supply of the plant cytosol

Plants rely on solar energy to synthesize ATP and NADPH for photosynthetic carbon fixation. Since a substantial proportion of cellular ATP is consumed in the cytosol, photosynthesis-derived ATP needs to be supplied there. While the triose phosphate shuttle and mitochondrial respiration can both deliver ATP to the cytosol, the significance of the different mechanisms in vivo has been difficult to assess. Although mitochondrial respiration is essential in plants, whether this is due to heterotrophic bottlenecks during plant development or rather a need for respiration in photosynthetically active cells, has not been resolved. In this study, we examined in vivo changes of cytosolic ATP concentration in response to light, employing a biosensing strategy in the moss Physcomitrium patens. Our measurements revealed increased cytosolic ATP concentration caused by photosynthetic activity. Moss tissue depleted of respiratory complex I showed decreased cytosolic ATP accumulation, highlighting a critical role of mitochondrial respiration in light-dependent ATP supply of the cytosol. Consistently, targeting mitochondrial ATP production directly, through the construction of mutants deficient in mitochondrial ATPase (complex V), led to drastic growth reduction, despite only minor alterations in photosynthetic electron transport activity. Since P. patens is photoautotrophic throughout its development, we conclude that heterotrophic bottlenecks cannot account for the indispensable role of mitochondrial respiration in plants. Instead, our results offer compelling evidence that mitochondrial respiration is essential for ATP provision to the cytosol in actively photosynthesizing cells. Mitochondrial respiration provides metabolic integration, ensuring a reliable supply of cytosolic ATP essential for supporting plant growth and development.

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↗

bioRxiv2023

A conserved ESCRT-II-like protein participates in the biogenesis and maintenance of thylakoid membranes

Thylakoids are membrane-bound compartments located in cyanobacteria and chloroplasts of plants and algae. They play an indispensable role in the light-driven reactions that enable photosynthetic organisms to convert water and carbon dioxide into oxygen and sugars. The biogenesis and maintenance of thylakoid membranes is a critical yet underappreciated area of research. One of the few known critical regulators of this process, VIPP1 (Vesicle-Inducing Protein in Plastids 1), was recently shown to be structurally similar to ESCRT-III proteins -- the first evidence for ESCRT-like (Endosomal Sorting Complex Required for Transport) machinery in chloroplasts. Here, we used an affinity purification approach in two distantly related photosynthetic eukaryotes, the green alga Chlamydomonas reinhardtii and the plant Arabidopsis thaliana, to discover proteins that interact with VIPP1. Among several newly identified proteins, we focused on a highly conserved but uncharacterized protein (VIPP1-Associated protein 1, VIA1) that robustly interacts with VIPP1 in both systems. VIA1 is predicted to contain a winged-helix domain, a characteristic feature of ESCRT-II proteins that mediates the interaction with ESCRT-III proteins. The absence of VIA1 causes thylakoid swelling upon exposure to high light in Chlamydomonas and defective thylakoid biogenesis in the newly emerging leaf tissue in Arabidopsis, thereby delaying chloroplast development in this tissue. We propose that VIA1 is part of a previously unrecognized chloroplast ESCRT-like system that plays a critical role in forming, remodeling, and repairing photosynthetic membranes. Significance StatementThylakoid membranes are essential for photosynthesis, yet their biogenesis and maintenance are poorly understood. Of the few known proteins involved in these processes, VIPP1 stands out due to its similarity to ESCRT-III, an integral component of the ESCRT machinery that is responsible for membrane remodeling and trafficking in the cytoplasm of eukaryotes. Here we report the discovery of VIA1, a conserved protein that interacts with VIPP1 and participates in thylakoid biogenesis and remodeling in two distantly related photosynthetic organisms. Because VIA1 contains a predicted winged-helix domain, a hallmark feature of ESCRT-II proteins that mediates the interaction with ESCRT-III proteins, our data support the hypothesis that universal, mechanistic principles govern membrane remodeling across all living organisms.

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↗

bioRxiv2022

Functional analysis of PsbS transmembrane domains through base editing in Physcomitrium patens

Plants exposed to light fluctuations are protected from photodamage by non-photochemical quenching (NPQ), a reversible mechanism that enables dissipation of excess absorbed energy as heat, which is essential for plant fitness and crop productivity. NPQ requires the activity of the membrane protein PsbS that, upon activation, interacts with antenna proteins, inducing their dissipative conformation. Here, we exploited base editing in the moss Physcomitrium patens to introduce in vivo specific amino acid changes and assess their impact on PsbS activity, targeting transmembrane regions to investigate their role in protein-protein interactions. This approach enabled the recognition of residues essential for protein stability and the identification of a hydrophobic cluster of amino acids with a seminal role in PsbS activity. This work provides new information on the PsbS molecular mechanism while also demonstrating the potential of base editing approaches for in planta gene function analysis.

plant biology↗

bioRxiv2020

Inactivation of mitochondrial Complex I stimulates chloroplast ATPase in Physcomitrella (Physcomitrium patens).

While light is the ultimate source of energy for photosynthetic organisms, mitochondrial respiration is still fundamental for supporting metabolism demand during the night or in heterotrophic tissues. Respiration is also important for the metabolism of photosynthetically active cells, acting as a sink for excess reduced molecules and source of substrates for anabolic pathways. In this work, we isolated Physcomitrella (Physcomitrium patens) plants with altered respiration by inactivating Complex I of the mitochondrial electron transport chain by independent targeting of two essential subunits. Results show that the inactivation of Complex I causes a strong growth impairment even in fully autotrophic conditions in tissues where all cells are photosynthetically active. Complex I mutants show major alterations in the stoichiometry of respiratory complexes while the composition of photosynthetic apparatus was substantially unaffected. Complex I mutants showed altered photosynthesis with higher yields of both Photosystems I and II. These are the consequence of a higher chloroplast ATPase activity that also caused a smaller {Delta}pH formation across thylakoid membranes as well as decreased photosynthetic control on cytochrome b6f, possibly to compensate for a deficit in ATP supply relative to demand in Complex I mutants. These results demonstrate that alteration of respiratory activity directly impacts photosynthesis in P. patens and that metabolic interaction between organelles is essential in their ability to use light energy for growth.

plant biology↗