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Andreas Holzinger - One of the best experts on this subject based on the ideXlab platform.
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Pre-akinete formation in Zygnema sp. from polar habitats is associated with metabolite re-arrangement.
Journal of experimental botany, 2020Co-Authors: Erwann Arc, Martina Pichrtova, Ilse Kranner, Andreas HolzingerAbstract:In streptophytic green algae in the genus Zygnema, pre-akinete formation is considered a key survival strategy under extreme environmental conditions in alpine and polar regions. The transition from young, dividing cells to pre-akinetes is associated with morphological changes and the accumulation of storage products. Understanding the underlying metabolic changes could provide insights into survival strategies in polar habitats. Here, GC-MS-based metabolite profiling was used to study the metabolic signature associated with pre-akinete formation in Zygnema sp. from polar regions under laboratory conditions, induced by water and nutrient depletion, or collected in the field. Light microscopy and TEM revealed drastic changes in chloroplast morphology and ultrastructure, degradation of starch grains, and accumulation of lipid bodies in pre-akinetes. Accordingly, the metabolite profiles upon pre-akinete formation reflected a gradual shift in metabolic activity. Compared with young cells, pre-akinetes showed an overall reduction in primary metabolites such as amino acids and intermediates of the tricarboxylic acid (TCA) cycle, consistent with a lower metabolic turnover, while they accumulated lipids and oligosaccharides. Overall, the transition to the pre-akinete stage involves re-allocation of photosynthetically fixed energy into storage instead of growth, supporting survival of extreme environmental conditions.
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metatranscriptomic and metabolite profiling reveals vertical heterogeneity within a Zygnema green algal mat from svalbard high arctic
Environmental Microbiology, 2019Co-Authors: Martina Pichrtova, Martin Rippin, Erwann Arc, Ilse Kranner, Burkhard Becker, Andreas HolzingerAbstract:Within streptophyte green algae Zygnematophyceae are the sister group to the land plants that inherited several traits conferring stress protection. Zygnema sp., a mat-forming alga thriving in extreme habitats, was collected from a field site in Svalbard, where the bottom layers are protected by the top layers. The two layers were investigated by a metatranscriptomic approach and GC-MS-based metabolite profiling. In the top layer, 6569 genes were significantly upregulated and 149 were downregulated. Upregulated genes coded for components of the photosynthetic apparatus, chlorophyll synthesis, early light-inducible proteins, cell wall and carbohydrate metabolism, including starch-degrading enzymes. An increase in maltose in the top layer and degraded starch grains at the ultrastructural levels corroborated these findings. Genes involved in amino acid, redox metabolism and DNA repair were upregulated. A total of 29 differentially accumulated metabolites (out of 173 identified ones) confirmed higher metabolic turnover in the top layer. For several of these metabolites, differential accumulation matched the transcriptional changes of enzymes involved in associated pathways. In summary, the findings support the hypothesis that in a Zygnema mat the top layer shields the bottom layers from abiotic stress factors such as excessive irradiation.
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The conjugating green alga Zygnema sp. (Zygnematophyceae) from the Arctic shows high frost tolerance in mature cells (pre-akinetes)
Protoplasma, 2019Co-Authors: Kateřina Trumhova, Andreas Holzinger, Sabrina Obwegeser, Gilbert Neuner, Martina PichrtovaAbstract:Green algae of the genus Zygnema form extensive mats and produce large amounts of biomass in shallow freshwater habitats. Environmental stresses including freezing may perturb these mats, which usually have only annual character. To estimate the limits of survival at subzero temperatures, freezing resistance of young Zygnema sp. (strain MP2011Skan) cells and pre-akinetes was investigated. Young, 2-week-old cultures were exposed to temperatures of 0 to – 14 °C at 2-K steps, whereas 8-month-old cultures were frozen from − 10 to – 70 °C at 10-K intervals. Cell viability after freezing was determined by 0.1% auramine O vital fluorescence staining and measurements of the effective quantum yield of photosystem II ( Ф _PSII). At – 8 °C, the young vegetative cells were unable to recover from severe frost damage. But temperatures even slightly below zero (− 2 °C) negatively affected the cells’ physiology. Single pre-akinetes could survive even at – 70 °C, but their LT_50 value was − 26.2 °C. Severe freezing cytorrhysis was observed via cryo-microscopy at – 10 °C, a temperature found to be lethal for young cells. The ultrastructure of young cells appeared unchanged at – 2 °C, but severe damage to biomembranes and formation of small foamy vacuoles was observed at – 10 °C. Pre-akinetes did not show ultrastructural changes at – 20 °C; however, vacuolization increased, and gas bubbles appeared at – 70 °C. Our results demonstrate that the formation of pre-akinetes increases freezing resistance. This adaptation is crucial for surviving the harsh temperature conditions prevailing in the High Arctic in winter and a key feature in seasonal dynamics of Zygnema sp.
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Homogalacturonan Accumulation in Cell Walls of the Green Alga Zygnema sp. (Charophyta) Increases Desiccation Resistance.
Frontiers in Plant Science, 2019Co-Authors: Klaus Herburger, Anzhou Xin, Andreas HolzingerAbstract:Abstract Land plants inherited several traits from their green algal ancestors (Zygnematophyceae), including a polysaccharide-rich cell wall, which is a prerequisite for terrestrial survival. A major component of both, land plant and Zygnematophyceaen cell walls is the pectin homogalacturonan (HG) and its high water holding capacity may have helped algae to colonize terrestrial habitats, characterised by water scarcity. To test this, HG was removed from the cell walls of Zygnema filaments by pectate lyase (PL) and their effective quantum yield of photosystem II (YII) as a proxy for photosynthetic performance was measured in response to desiccation stress by pulse amplitude modulation (PAM). Old filaments were found to contain more HG and are more resistant against desiccation stress but relatively lose more desiccation resistance after HG removal than young filaments. After rehydration, the photosynthetic performance recovered less efficiently in filaments with a HG content reduced by PL, independently of filament age. Immunolabelling showed that partially or un-methylesterified HG occurs throughout the longitudinal cell walls of both young and old filaments, while no labelling signal occurred when filaments were treated with PL prior labelling. This confirmed that most HG can be removed from the cell walls by PL. The initial labelling pattern was restored after ~3 days. A different form of methylesterified HG was restricted to cell poles and cross cell walls.. In conclusion, it was shown that the accumulation of HG in Zygnema filaments increases their resistance against desiccation stress. This trait might have played an important role during the colonization of land by Zygnematophyceae, which founded the evolution of all land plants.
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Presentation_1_Arabinogalactan Proteins and the Extracellular Matrix of Charophytes: A Sticky Business.pptx
2019Co-Authors: Kattia Palacio-lópez, Andreas Holzinger, Berke Tinaz, David S. DomozychAbstract:Charophytes represent the group of green algae whose ancestors invaded land and ultimately gave rise to land plants 450 million years ago. While Zygnematophyceae are believed to be the direct sister lineage to embryophytes, different members of this group (Penium, Spirogyra, Zygnema) and the advanced thallus forming Coleochaete as well as the sarcinoid basal streptophyte Chlorokybus were investigated concerning their vegetative extracellular matrix (ECM) properties. Many taxa exhibit adhesion phenomena that are critical for affixing to a substrate or keeping cells together in a thallus, however, there is a great variety in possible reactions to e.g., wounding. In this study an analysis of adhesion mechanisms revealed that arabinogalactan proteins (AGPs) are most likely key adhesion molecules. Through use of monoclonal antibodies (JIM13) or the Yariv reagent, AGPs were located in cell surface sheaths and cell walls that were parts of the adhesion focal zones on substrates including wound induced rhizoid formation. JIM5, detecting highly methyl-esterfied homoglacturonan and JIM8, an antibody detecting AGP glycan and LM6 detecting arabinans were also tested and a colocalization was found in several examples (e.g., Zygnema) suggesting an interplay between these components. AGPs have been described in this study to perform both, cell to cell adhesion in algae forming thalli and cell to surface adhesion in the filamentous forms. These findings enable a broader evolutionary understanding of the function of AGPs in charophyte green algae.
Martina Pichrtova - One of the best experts on this subject based on the ideXlab platform.
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Pre-akinete formation in Zygnema sp. from polar habitats is associated with metabolite re-arrangement.
Journal of experimental botany, 2020Co-Authors: Erwann Arc, Martina Pichrtova, Ilse Kranner, Andreas HolzingerAbstract:In streptophytic green algae in the genus Zygnema, pre-akinete formation is considered a key survival strategy under extreme environmental conditions in alpine and polar regions. The transition from young, dividing cells to pre-akinetes is associated with morphological changes and the accumulation of storage products. Understanding the underlying metabolic changes could provide insights into survival strategies in polar habitats. Here, GC-MS-based metabolite profiling was used to study the metabolic signature associated with pre-akinete formation in Zygnema sp. from polar regions under laboratory conditions, induced by water and nutrient depletion, or collected in the field. Light microscopy and TEM revealed drastic changes in chloroplast morphology and ultrastructure, degradation of starch grains, and accumulation of lipid bodies in pre-akinetes. Accordingly, the metabolite profiles upon pre-akinete formation reflected a gradual shift in metabolic activity. Compared with young cells, pre-akinetes showed an overall reduction in primary metabolites such as amino acids and intermediates of the tricarboxylic acid (TCA) cycle, consistent with a lower metabolic turnover, while they accumulated lipids and oligosaccharides. Overall, the transition to the pre-akinete stage involves re-allocation of photosynthetically fixed energy into storage instead of growth, supporting survival of extreme environmental conditions.
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The conjugating green alga Zygnema sp. (Zygnematophyceae) from the Arctic shows high frost tolerance in mature cells (pre-akinetes)
Protoplasma, 2019Co-Authors: Kateřina Trumhova, Andreas Holzinger, Sabrina Obwegeser, Gilbert Neuner, Martina PichrtovaAbstract:Green algae of the genus Zygnema form extensive mats and produce large amounts of biomass in shallow freshwater habitats. Environmental stresses including freezing may perturb these mats, which usually have only annual character. To estimate the limits of survival at subzero temperatures, freezing resistance of young Zygnema sp. (strain MP2011Skan) cells and pre-akinetes was investigated. Young, 2-week-old cultures were exposed to temperatures of 0 to – 14 °C at 2-K steps, whereas 8-month-old cultures were frozen from − 10 to – 70 °C at 10-K intervals. Cell viability after freezing was determined by 0.1% auramine O vital fluorescence staining and measurements of the effective quantum yield of photosystem II ( Ф _PSII). At – 8 °C, the young vegetative cells were unable to recover from severe frost damage. But temperatures even slightly below zero (− 2 °C) negatively affected the cells’ physiology. Single pre-akinetes could survive even at – 70 °C, but their LT_50 value was − 26.2 °C. Severe freezing cytorrhysis was observed via cryo-microscopy at – 10 °C, a temperature found to be lethal for young cells. The ultrastructure of young cells appeared unchanged at – 2 °C, but severe damage to biomembranes and formation of small foamy vacuoles was observed at – 10 °C. Pre-akinetes did not show ultrastructural changes at – 20 °C; however, vacuolization increased, and gas bubbles appeared at – 70 °C. Our results demonstrate that the formation of pre-akinetes increases freezing resistance. This adaptation is crucial for surviving the harsh temperature conditions prevailing in the High Arctic in winter and a key feature in seasonal dynamics of Zygnema sp.
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metatranscriptomic and metabolite profiling reveals vertical heterogeneity within a Zygnema green algal mat from svalbard high arctic
Environmental Microbiology, 2019Co-Authors: Martina Pichrtova, Martin Rippin, Erwann Arc, Ilse Kranner, Burkhard Becker, Andreas HolzingerAbstract:Within streptophyte green algae Zygnematophyceae are the sister group to the land plants that inherited several traits conferring stress protection. Zygnema sp., a mat-forming alga thriving in extreme habitats, was collected from a field site in Svalbard, where the bottom layers are protected by the top layers. The two layers were investigated by a metatranscriptomic approach and GC-MS-based metabolite profiling. In the top layer, 6569 genes were significantly upregulated and 149 were downregulated. Upregulated genes coded for components of the photosynthetic apparatus, chlorophyll synthesis, early light-inducible proteins, cell wall and carbohydrate metabolism, including starch-degrading enzymes. An increase in maltose in the top layer and degraded starch grains at the ultrastructural levels corroborated these findings. Genes involved in amino acid, redox metabolism and DNA repair were upregulated. A total of 29 differentially accumulated metabolites (out of 173 identified ones) confirmed higher metabolic turnover in the top layer. For several of these metabolites, differential accumulation matched the transcriptional changes of enzymes involved in associated pathways. In summary, the findings support the hypothesis that in a Zygnema mat the top layer shields the bottom layers from abiotic stress factors such as excessive irradiation.
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Molecular and morphological diversity of Zygnema and Zygnemopsis (Zygnematophyceae, Streptophyta) from Svalbard (High Arctic)
European journal of phycology, 2018Co-Authors: Martina Pichrtova, Kateřina Trumhova, David Ryšánek, Andreas Holzinger, Jana Kulichová, Tereza Šoljaková, Yvonne NemcovaAbstract:Filamentous conjugating green microalgae (Zygnematophyceae, Streptophyta) belong to the most common primary producers in polar hydro-terrestrial environments such as meltwater streamlets and shallow pools. The mats formed by these organisms are mostly composed of sterile filaments with Zygnema morphology, but the extent of their diversity remains unknown. Traditional taxonomy of this group is based on reproductive morphology, but sexual reproduction (conjugation and formation of resistant zygospores) is very rare in extreme conditions. In the present study we gave the first record of zygospore formation in Svalbard field samples, and identified conjugating filaments as Zygnemopsis lamellata and Zygnema cf. calosporum. We applied molecular phylogeny to study genetic diversity of sterile Zygnema filaments from Svalbard in the High Arctic. Based on analysis of 143 rbcL sequences, we revealed a surprisingly high molecular diversity: 12 Arctic Zygnema genotypes and one Zygnemopsis genotype were found. In addition, we characterized individual Arctic genotypes based on cell width and chloroplast morphology using light and confocal laser scanning microscopy. Our findings highlight the importance of a molecular approach when working with sterile filamentous Zygnematophyceae, as hidden diversity might be very beneficial for adaptation to harsh environmental conditions, and experimental results could be misinterpreted when hidden diversity is neglected.
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arctic antarctic and temperate green algae Zygnema spp under uv b stress vegetative cells perform better than pre akinetes
Protoplasma, 2018Co-Authors: Andreas Holzinger, Siegfried Aigner, Kateřina Trumhova, Philippe Schmittkopplin, Andreas Albert, Martina PichrtovaAbstract:Species of Zygnema form macroscopically visible mats in polar and temperate terrestrial habitats, where they are exposed to environmental stresses. Three previously characterized isolates (Arctic Zygnema sp. B, Antarctic Zygnema sp. C, and temperate Zygnema sp. S) were tested for their tolerance to experimental UV radiation. Samples of young vegetative cells (1 month old) and pre-akinetes (6 months old) were exposed to photosynthetically active radiation (PAR, 400–700 nm, 400 μmol photons m−2 s−1) in combination with experimental UV-A (315–400 nm, 5.7 W m−2, no UV-B), designated as PA, or UV-A (10.1 W m−2) + UV-B (280–315 nm, 1.0 W m−2), designated as PAB. The experimental period lasted for 74 h; the radiation period was 16 h PAR/UV-A per day, or with additional UV-B for 14 h per day. The effective quantum yield, generally lower in pre-akinetes, was mostly reduced during the UV treatment, and recovery was significantly higher in young vegetative cells vs. pre-akinetes during the experiment. Analysis of the deepoxidation state of the xanthophyll-cycle pigments revealed a statistically significant (p < 0.05) increase in Zygnema spp. C and S. The content of UV-absorbing phenolic compounds was significantly higher (p < 0.05) in young vegetative cells compared to pre-akinetes. In young vegetative Zygnema sp. S, these phenolic compounds significantly increased (p < 0.05) upon PA and PAB. Transmission electron microscopy showed an intact ultrastructure with massive starch accumulations at the pyrenoids under PA and PAB. A possible increase in electron-dense bodies in PAB-treated cells and the occurrence of cubic membranes in the chloroplasts are likely protection strategies. Metabolite profiling by non-targeted RP-UHPLC-qToF-MS allowed a clear separation of the strains, but could not detect changes due to the PA and PAB treatments. Six hundred seventeen distinct molecular masses were detected, of which around 200 could be annotated from databases. These results indicate that young vegetative cells can adapt better to the experimental UV-B stress than pre-akinetes.
Klaus Herburger - One of the best experts on this subject based on the ideXlab platform.
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Homogalacturonan Accumulation in Cell Walls of the Green Alga Zygnema sp. (Charophyta) Increases Desiccation Resistance.
Frontiers in Plant Science, 2019Co-Authors: Klaus Herburger, Anzhou Xin, Andreas HolzingerAbstract:Abstract Land plants inherited several traits from their green algal ancestors (Zygnematophyceae), including a polysaccharide-rich cell wall, which is a prerequisite for terrestrial survival. A major component of both, land plant and Zygnematophyceaen cell walls is the pectin homogalacturonan (HG) and its high water holding capacity may have helped algae to colonize terrestrial habitats, characterised by water scarcity. To test this, HG was removed from the cell walls of Zygnema filaments by pectate lyase (PL) and their effective quantum yield of photosystem II (YII) as a proxy for photosynthetic performance was measured in response to desiccation stress by pulse amplitude modulation (PAM). Old filaments were found to contain more HG and are more resistant against desiccation stress but relatively lose more desiccation resistance after HG removal than young filaments. After rehydration, the photosynthetic performance recovered less efficiently in filaments with a HG content reduced by PL, independently of filament age. Immunolabelling showed that partially or un-methylesterified HG occurs throughout the longitudinal cell walls of both young and old filaments, while no labelling signal occurred when filaments were treated with PL prior labelling. This confirmed that most HG can be removed from the cell walls by PL. The initial labelling pattern was restored after ~3 days. A different form of methylesterified HG was restricted to cell poles and cross cell walls.. In conclusion, it was shown that the accumulation of HG in Zygnema filaments increases their resistance against desiccation stress. This trait might have played an important role during the colonization of land by Zygnematophyceae, which founded the evolution of all land plants.
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localisation and substrate specificities of transglycanases in charophyte algae relate to development and morphology
Journal of Cell Science, 2018Co-Authors: Klaus Herburger, Louise Ryan, Zoe A Popper, Andreas HolzingerAbstract:Cell wall-modifying enzymes were previously investigated in charophyte green algae (CGA) from cultures of uniform age, giving limited insight into their roles. Therefore, we investigated the in situ localisation and specificity of enzymes acting on hemicelluloses in CGA genera of different morphologies and developmental stages. In vivo transglycosylation between xyloglucan and an endogenous donor in filamentous Klebsormidium and Zygnema showed action in longitudinal cell walls of young (1 month) but not old cells (1 year), suggesting involvement in cell growth. Contrastingly, in parenchymatous Chara , transglycanase action occurred in all cell planes. In Klebsormidium and Zygnema , enzyme action predominately co-localised with xyloglucans and mannans, to a lesser extent mixed-linkage β-glucan (MLG), indicating predominantly xyloglucan:xyloglucan endotransglucosylase (XET). Novel transglycosylation activities between xyloglucan and xylan, and xyloglucan and galactomannan were identified in vitro , in both genera. Our results show that several cell wall-modifying enzymes are present in CGA and that differences in morphology and cell age are related to enzyme localisation and specificity. This indicates an evolutionary significance of cell wall modifications, as similar changes are known from their immediate descendants, the land plants.
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Europe PM
2016Co-Authors: Rosalina Stancheva, Robert G. Sheath, John D. Hall, Klaus Herburger, Louise A Lewis, Richard M. Mccourt, Andreas HolzingerAbstract:Zygogonium ericetorum, the type species of the genus, was studied from a natural population collected in Mt. Schönwieskopf, Tyrol, Austria. Generic concepts of Zygogonium and Zygnema were tested with atpB, psbC, and rbcL gene sequence analysis, which showed a sister relationship © 2014 The Authors This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 2Author for correspondence
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Localization and Quantification of Callose in the Streptophyte Green Algae Zygnema and Klebsormidium: Correlation with Desiccation Tolerance
2016Co-Authors: Klaus Herburger, Andreas HolzingerAbstract:Freshwater green algae started to colonise terrestrial habitats about 460 million years ago, giving rise to the evolution of land plants. Today, several streptophyte green algae occur in aero-terrestrial habitats with unpredictable fluctuations in water availability, severing as ideal models for investigating desiccation tolerance. We tested the hypothesis that callose, a β-D-1,3-glucan, is incorporated specifically in strained areas of the cell wall due to cellular water loss, implicating a contribution to desiccation tolerance. In the early diverging genus Klebsormidium, callose was drastically increased already upon 30 min of desiccation stress. Localization studies demonstrated an increase of callose in the undulating cross cell walls during cellular water loss, allowing a regulated shrinkage and expansion after rehydration. This correlates with a high desiccation tolerance demonstrated by a full recovery of the photosynthetic yield visualized at the subcellular level by Imaging-PAM. Furthermore, abundant callose in terminal cell walls might facilitate cell detachment to release dispersal units. In contrast, in the late diverging Zygnema callose content did not change upon desiccation for up to 3.5 h and was primarily localized in the corners between individual and at terminal cells. While these callose deposits still imply reduction of mechanical damage, the photosynthetic yield did not recover fully in the investigated young cultures of Zygnema upon rehydration. The abundance and specific localization of callose correlates with the higher desiccation tolerance in Klebsormidium when compared to Zygnema. Keywords aero-terrestrial green algae; cell wall; evolutionary biology; Imaging-PAM; phylogeny; terrestrialization This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial Licens
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Localization and Quantification of Callose in the Streptophyte Green Algae Zygnema and Klebsormidium: Correlation with Desiccation Tolerance
Plant & cell physiology, 2015Co-Authors: Klaus Herburger, Andreas HolzingerAbstract:Freshwater green algae started to colonize terrestrial habitats about 460 million years ago, giving rise to the evolution of land plants. Today, several streptophyte green algae occur in aero-terrestrial habitats with unpredictable fluctuations in water availability, serving as ideal models for investigating desiccation tolerance. We tested the hypothesis that callose, a β-d-1,3-glucan, is incorporated specifically in strained areas of the cell wall due to cellular water loss, implicating a contribution to desiccation tolerance. In the early diverging genus Klebsormidium, callose was drastically increased already after 30 min of desiccation stress. Localization studies demonstrated an increase in callose in the undulating cross cell walls during cellular water loss, allowing a regulated shrinkage and expansion after rehydration. This correlates with a high desiccation tolerance demonstrated by a full recovery of the photosynthetic yield visualized at the subcellular level by Imaging-PAM. Furthermore, abundant callose in terminal cell walls might facilitate cell detachment to release dispersal units. In contrast, in the late diverging Zygnema, the callose content did not change upon desiccation for up to 3.5 h and was primarily localized in the corners between individual cells and at terminal cells. While these callose deposits still imply reduction of mechanical damage, the photosynthetic yield did not recover fully in the investigated young cultures of Zygnema upon rehydration. The abundance and specific localization of callose correlates with the higher desiccation tolerance in Klebsormidium when compared with Zygnema.
Yanbin Yin - One of the best experts on this subject based on the ideXlab platform.
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Zygnema circumcarinatum UTEX 1559 chloroplast and mitochondrial genomes provide insight into land plant evolution.
Journal of experimental botany, 2020Co-Authors: Lauren M Orton, Elisabeth Fitzek, Xuehuan Feng, W. Scott Grayburn, Jeffrey P. Mower, Kan Liu, Chi Zhang, Melvin R. Duvall, Yanbin YinAbstract:The complete chloroplast and mitochondrial genomes of Charophyta have shed new light on land plant terrestrialization. Here, we report the organellar genomes of the Zygnema circumcarinatum strain UTEX 1559, and a comparative genomics investigation of 33 plastomes and 18 mitogenomes of Chlorophyta, Charophyta (including UTEX 1559 and its conspecific relative SAG 698-1a), and Embryophyta. Gene presence/absence was determined across these plastomes and mitogenomes. A comparison between the plastomes of UTEX 1559 (157 548 bp) and SAG 698-1a (165 372 bp) revealed very similar gene contents, but substantial genome rearrangements. Surprisingly, the two plastomes share only 85.69% nucleotide sequence identity. The UTEX 1559 mitogenome size is 215 954 bp, the largest among all sequenced Charophyta. Interestingly, this large mitogenome contains a 50 kb region without homology to any other organellar genomes, which is flanked by two 86 bp direct repeats and contains 15 ORFs. These ORFs have significant homology to proteins from bacteria and plants with functions such as primase, RNA polymerase, and DNA polymerase. We conclude that (i) the previously published SAG 698-1a plastome is probably from a different Zygnema species, and (ii) the 50 kb region in the UTEX 1559 mitogenome might be recently acquired as a mobile element.
Kateřina Trumhova - One of the best experts on this subject based on the ideXlab platform.
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The conjugating green alga Zygnema sp. (Zygnematophyceae) from the Arctic shows high frost tolerance in mature cells (pre-akinetes)
Protoplasma, 2019Co-Authors: Kateřina Trumhova, Andreas Holzinger, Sabrina Obwegeser, Gilbert Neuner, Martina PichrtovaAbstract:Green algae of the genus Zygnema form extensive mats and produce large amounts of biomass in shallow freshwater habitats. Environmental stresses including freezing may perturb these mats, which usually have only annual character. To estimate the limits of survival at subzero temperatures, freezing resistance of young Zygnema sp. (strain MP2011Skan) cells and pre-akinetes was investigated. Young, 2-week-old cultures were exposed to temperatures of 0 to – 14 °C at 2-K steps, whereas 8-month-old cultures were frozen from − 10 to – 70 °C at 10-K intervals. Cell viability after freezing was determined by 0.1% auramine O vital fluorescence staining and measurements of the effective quantum yield of photosystem II ( Ф _PSII). At – 8 °C, the young vegetative cells were unable to recover from severe frost damage. But temperatures even slightly below zero (− 2 °C) negatively affected the cells’ physiology. Single pre-akinetes could survive even at – 70 °C, but their LT_50 value was − 26.2 °C. Severe freezing cytorrhysis was observed via cryo-microscopy at – 10 °C, a temperature found to be lethal for young cells. The ultrastructure of young cells appeared unchanged at – 2 °C, but severe damage to biomembranes and formation of small foamy vacuoles was observed at – 10 °C. Pre-akinetes did not show ultrastructural changes at – 20 °C; however, vacuolization increased, and gas bubbles appeared at – 70 °C. Our results demonstrate that the formation of pre-akinetes increases freezing resistance. This adaptation is crucial for surviving the harsh temperature conditions prevailing in the High Arctic in winter and a key feature in seasonal dynamics of Zygnema sp.
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Molecular and morphological diversity of Zygnema and Zygnemopsis (Zygnematophyceae, Streptophyta) from Svalbard (High Arctic)
European journal of phycology, 2018Co-Authors: Martina Pichrtova, Kateřina Trumhova, David Ryšánek, Andreas Holzinger, Jana Kulichová, Tereza Šoljaková, Yvonne NemcovaAbstract:Filamentous conjugating green microalgae (Zygnematophyceae, Streptophyta) belong to the most common primary producers in polar hydro-terrestrial environments such as meltwater streamlets and shallow pools. The mats formed by these organisms are mostly composed of sterile filaments with Zygnema morphology, but the extent of their diversity remains unknown. Traditional taxonomy of this group is based on reproductive morphology, but sexual reproduction (conjugation and formation of resistant zygospores) is very rare in extreme conditions. In the present study we gave the first record of zygospore formation in Svalbard field samples, and identified conjugating filaments as Zygnemopsis lamellata and Zygnema cf. calosporum. We applied molecular phylogeny to study genetic diversity of sterile Zygnema filaments from Svalbard in the High Arctic. Based on analysis of 143 rbcL sequences, we revealed a surprisingly high molecular diversity: 12 Arctic Zygnema genotypes and one Zygnemopsis genotype were found. In addition, we characterized individual Arctic genotypes based on cell width and chloroplast morphology using light and confocal laser scanning microscopy. Our findings highlight the importance of a molecular approach when working with sterile filamentous Zygnematophyceae, as hidden diversity might be very beneficial for adaptation to harsh environmental conditions, and experimental results could be misinterpreted when hidden diversity is neglected.
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arctic antarctic and temperate green algae Zygnema spp under uv b stress vegetative cells perform better than pre akinetes
Protoplasma, 2018Co-Authors: Andreas Holzinger, Siegfried Aigner, Kateřina Trumhova, Philippe Schmittkopplin, Andreas Albert, Martina PichrtovaAbstract:Species of Zygnema form macroscopically visible mats in polar and temperate terrestrial habitats, where they are exposed to environmental stresses. Three previously characterized isolates (Arctic Zygnema sp. B, Antarctic Zygnema sp. C, and temperate Zygnema sp. S) were tested for their tolerance to experimental UV radiation. Samples of young vegetative cells (1 month old) and pre-akinetes (6 months old) were exposed to photosynthetically active radiation (PAR, 400–700 nm, 400 μmol photons m−2 s−1) in combination with experimental UV-A (315–400 nm, 5.7 W m−2, no UV-B), designated as PA, or UV-A (10.1 W m−2) + UV-B (280–315 nm, 1.0 W m−2), designated as PAB. The experimental period lasted for 74 h; the radiation period was 16 h PAR/UV-A per day, or with additional UV-B for 14 h per day. The effective quantum yield, generally lower in pre-akinetes, was mostly reduced during the UV treatment, and recovery was significantly higher in young vegetative cells vs. pre-akinetes during the experiment. Analysis of the deepoxidation state of the xanthophyll-cycle pigments revealed a statistically significant (p < 0.05) increase in Zygnema spp. C and S. The content of UV-absorbing phenolic compounds was significantly higher (p < 0.05) in young vegetative cells compared to pre-akinetes. In young vegetative Zygnema sp. S, these phenolic compounds significantly increased (p < 0.05) upon PA and PAB. Transmission electron microscopy showed an intact ultrastructure with massive starch accumulations at the pyrenoids under PA and PAB. A possible increase in electron-dense bodies in PAB-treated cells and the occurrence of cubic membranes in the chloroplasts are likely protection strategies. Metabolite profiling by non-targeted RP-UHPLC-qToF-MS allowed a clear separation of the strains, but could not detect changes due to the PA and PAB treatments. Six hundred seventeen distinct molecular masses were detected, of which around 200 could be annotated from databases. These results indicate that young vegetative cells can adapt better to the experimental UV-B stress than pre-akinetes.
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Arctic, Antarctic, and temperate green algae Zygnema spp. under UV-B stress: vegetative cells perform better than pre-akinetes.
Protoplasma, 2018Co-Authors: Andreas Holzinger, Siegfried Aigner, Kateřina Trumhova, Andreas Albert, Jenny Uhl, Philippe Schmitt-kopplin, Martina PichrtovaAbstract:Species of Zygnema form macroscopically visible mats in polar and temperate terrestrial habitats, where they are exposed to environmental stresses. Three previously characterized isolates (Arctic Zygnema sp. B, Antarctic Zygnema sp. C, and temperate Zygnema sp. S) were tested for their tolerance to experimental UV radiation. Samples of young vegetative cells (1 month old) and pre-akinetes (6 months old) were exposed to photosynthetically active radiation (PAR, 400–700 nm, 400 μmol photons m−2 s−1) in combination with experimental UV-A (315–400 nm, 5.7 W m−2, no UV-B), designated as PA, or UV-A (10.1 W m−2) + UV-B (280–315 nm, 1.0 W m−2), designated as PAB. The experimental period lasted for 74 h; the radiation period was 16 h PAR/UV-A per day, or with additional UV-B for 14 h per day. The effective quantum yield, generally lower in pre-akinetes, was mostly reduced during the UV treatment, and recovery was significantly higher in young vegetative cells vs. pre-akinetes during the experiment. Analysis of the deepoxidation state of the xanthophyll-cycle pigments revealed a statistically significant (p
