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1.
Ecotoxicol Environ Saf ; 208: 111630, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33396150

RESUMO

The non-steroidal anti-inflammatory drug diclofenac (DCF) is one of the commonly used and frequently detected drugs in water bodies, and several studies indicate its toxic effect on plants and algae. Studies performed with asynchronous Chlamydomonas reinhardtii cultures indicated that DCF inhibit the growth of population of the algae. Here, a synchronous population of C. reinhardtii, in which all cells are in the same developmental phase, is used. Following changes in cells size, photosynthetic activity and gene expression, we could compare, at the level of single cell, DCF-mediated effects with the effects caused by atrazine, a triazine herbicide that inhibits photosynthesis and triggers oxidative stress. Application of DCF and atrazine at the beginning of the cell cycle allowed us to follow the changes occurring in the cells in the subsequent stages of their development. Synchronized Chlamydomonas reinhardtii cultures (strain CC-1690, wild type) were exposed to diclofenac sodium salt (135 mg/L) or atrazine (77.6 µg/L). The cell suspension was sampled hourly (0-10 h) in the light period of the cell cycle to determine cell number and volume, photosynthetic pigment content, chlorophyll a fluorescence (OJIP test) in vivo, and selected gene expression (real-time qPCR), namely psbA, psaA, FSD1, MSD3 and APX1. The two toxicants differently influenced C. reinhardtii cells. Both substances decreased photosynthetic "vitality" (PI - performance index) of the cells, albeit for different reasons. While atrazine significantly disrupted the photosynthetic electron transport, resulting in excessive production of reactive oxygen species (ROS) and limited cell growth, DCF caused silencing of photosystem II (PSII) reaction centers, transforming them into "heat sinks", thus preventing significant ROS overproduction. Oxidative stress caused by atrazine was the probable reason for the rapid appearance of phytotoxic action soon after entering the cells, while the effects of DCF could only be seen several hours after treatment. A comparison of DCF-caused effects with the effects caused by atrazine led us to conclude that, although DCF cannot be regarded as typical photosynthetic herbicide, it exhibits an algicidal activity and can be potentially dangerous for aquatic plants and algae.


Assuntos
Chlamydomonas reinhardtii/fisiologia , Diclofenaco/toxicidade , Herbicidas/toxicidade , Fotossíntese/efeitos dos fármacos , Atrazina/metabolismo , Atrazina/toxicidade , Chlamydomonas reinhardtii/efeitos dos fármacos , Clorofila A/metabolismo , Clorófitas/metabolismo , Diclofenaco/metabolismo , Transporte de Elétrons/efeitos dos fármacos , Herbicidas/metabolismo , Estresse Oxidativo/efeitos dos fármacos , Complexo de Proteína do Fotossistema II/metabolismo , Espécies Reativas de Oxigênio/metabolismo
2.
Sci Rep ; 10(1): 13287, 2020 08 06.
Artigo em Inglês | MEDLINE | ID: mdl-32764698

RESUMO

Ascorbate peroxidase (APX; EC 1.11.1.11) activity and transcript levels of CrAPX1, CrAPX2, and CrAPX4 of Chlamydomonas reinhardtii increased under 1,400 µE·m-2·s-1 condition (HL). CrAPX4 expression was the most significant. So, CrAPX4 was downregulated using amiRNA technology to examine the role of APX for HL acclimation. The CrAPX4 knockdown amiRNA lines showed low APX activity and CrAPX4 transcript level without a change in CrAPX1 and CrAPX2 transcript levels, and monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) activities and transcript levels. Upon exposure to HL, CrAPX4 knockdown amiRNA lines appeared a modification in the expression of genes encoding the enzymes in the ascorbate-glutathione cycle, including an increase in transcript level of CrVTC2, a key enzyme for ascorbate (AsA) biosynthesis but a decrease in MDAR and DHAR transcription and activity after 1 h, followed by increases in reactive oxygen species production and lipid peroxidation after 6 h and exhibited cell death after 9 h. Besides, AsA content and AsA/DHA (dehydroascorbate) ratio decreased in CrAPX4 knockdown amiRNA lines after prolonged HL treatment. Thus, CrAPX4 induction together with its association with the modulation of MDAR and DHAR expression for AsA regeneration is critical for Chlamydomonas to cope with photo-oxidative stress.


Assuntos
Ascorbato Peroxidases/metabolismo , Chlamydomonas reinhardtii/enzimologia , Chlamydomonas reinhardtii/efeitos da radiação , Luz/efeitos adversos , Estresse Oxidativo/efeitos da radiação , Ascorbato Peroxidases/deficiência , Ascorbato Peroxidases/genética , Chlamydomonas reinhardtii/metabolismo , Chlamydomonas reinhardtii/fisiologia , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Técnicas de Silenciamento de Genes
3.
PLoS Genet ; 16(6): e1008814, 2020 06.
Artigo em Inglês | MEDLINE | ID: mdl-32555650

RESUMO

The circadian clocks in chlorophyte algae have been studied in two model organisms, Chlamydomonas reinhardtii and Ostreococcus tauri. These studies revealed that the chlorophyte clocks include some genes that are homologous to those of the angiosperm circadian clock. However, the genetic network architectures of the chlorophyte clocks are largely unknown, especially in C. reinhardtii. In this study, using C. reinhardtii as a model, we characterized RHYTHM OF CHLOROPLAST (ROC) 75, a clock gene encoding a putative GARP DNA-binding transcription factor similar to the clock proteins LUX ARRHYTHMO (LUX, also called PHYTOCLOCK 1 [PCL1]) and BROTHER OF LUX ARRHYTHMO (BOA, also called NOX) of the angiosperm Arabidopsis thaliana. We observed that ROC75 is a day/subjective day-phase-expressed nuclear-localized protein that associates with some night-phased clock genes and represses their expression. This repression may be essential for the gating of reaccumulation of the other clock-related GARP protein, ROC15, after its light-dependent degradation. The restoration of ROC75 function in an arrhythmic roc75 mutant under constant darkness leads to the resumption of circadian oscillation from the subjective dawn, suggesting that the ROC75 restoration acts as a morning cue for the C. reinhardtii clock. Our study reveals a part of the genetic network of C. reinhardtii clock that could be considerably different from that of A. thaliana.


Assuntos
Chlamydomonas reinhardtii/fisiologia , Relógios Circadianos/genética , Regulação da Expressão Gênica de Plantas , Proteínas de Plantas/fisiologia , Fatores de Transcrição/fisiologia , Cloroplastos/fisiologia , Ritmo Circadiano/genética , Redes Reguladoras de Genes/fisiologia , Mutação , Fotoperíodo , Plantas Geneticamente Modificadas
4.
Curr Biol ; 30(4): 634-644.e7, 2020 02 24.
Artigo em Inglês | MEDLINE | ID: mdl-31928875

RESUMO

Most eukaryotic cells execute binary division after each mass doubling in order to maintain size homeostasis by coordinating cell growth and division. By contrast, the photosynthetic green alga Chlamydomonas can grow more than 8-fold during daytime and then, at night, undergo rapid cycles of DNA replication, mitosis, and cell division, producing up to 16 daughter cells. Here, we propose a mechanistic model for multiple-fission cycles and cell-size control in Chlamydomonas. The model comprises a light-sensitive and size-dependent biochemical toggle switch that acts as a sizer, guarding transitions into and exit from a phase of cell-division cycle oscillations. This simple "sizer-oscillator" arrangement reproduces the experimentally observed features of multiple-fission cycles and the response of Chlamydomonas cells to different light-dark regimes. Our model also makes specific predictions about the size dependence of the time of onset of cell division after cells are transferred from light to dark conditions, and we confirm these predictions by single-cell experiments. Collectively, our results provide a new perspective on the concept of a "commitment point" during the growth of Chlamydomonas cells and hint at intriguing similarities of cell-size control in different eukaryotic lineages.


Assuntos
Ciclo Celular/efeitos da radiação , Chlamydomonas reinhardtii/fisiologia , Luz , Chlamydomonas reinhardtii/crescimento & desenvolvimento , Chlamydomonas reinhardtii/efeitos da radiação
5.
BMC Plant Biol ; 20(1): 22, 2020 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-31931713

RESUMO

BACKGROUND: Proteasomes remove regulatory proteins in eukaryotic cells, and control a variety of plant processes. Proteasomes are localized to the cytosol and nuclear, but their role in plant biology has recently been extended to chloroplasts, where it regulates TOC complex. This is turn controls the import of nuclear-encoded chloroplastic proteins, which remodels the chloroplast proteome and facilitates proper developmental transitions. Proteasomal regulation of the TOC complex also alleviates stressors that generate reactive oxygen species. These recent advances motivated us to determine if proteasome inhibition rapidly alters photosynthetic processes stemming from photoinhibition induced by high light. RESULTS: The short-term effects of proteasome inhibition on photosystem II during light stress was measured in Chlamydomonas reinhardtii, which allowed the dual monitoring of both chlorophyll fluorescence and cell viability. After 48 h at low light, proteasome inhibition did not affect viability or photochemistiry, but decreased cell concentration and increased cell volume. Two hours of high light stress impaired the efficiency of photosystem II in proteasome-inhibited cells, as determined by a decrease in Fv/Fm and the electron transport rate. Elevated photoinhibition in proteasome inhibited cells was not caused by a decrease in cell viability or chlorophyll content. Recovery from photoinhibition was attenuated in MG132-treated cells, and suppressed growth of a reestablished culture. Proteasome inhibition decreased de novo protein synthesis, which possibly constrained the ability to remodel the plastid proteome, and thus hampering the ability to adjust to high light stress. CONCLUSION: The proteasome is implicated in protecting photosystem II from photoinhibition. In addition to high light stress, other stressors- including metals, drought, and salt- are also known to generate reactive oxygen species localized to the chloroplast. Therefore, proteasome maintenance in plants may help protect photosynthesis during abiotic stress, which could increase crop yield during adverse conditions.


Assuntos
Chlamydomonas reinhardtii/fisiologia , Complexo de Proteína do Fotossistema II/metabolismo , Complexo de Endopeptidases do Proteassoma/metabolismo , Inibidores de Proteassoma/metabolismo , Chlamydomonas reinhardtii/citologia , Clorofila/metabolismo , Cloroplastos/metabolismo , Leupeptinas/metabolismo , Luz , Fotossíntese , Estresse Fisiológico
6.
Mol Cells ; 43(1): 48-57, 2020 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-31910336

RESUMO

The microalga Chlamydomonas reinhardtii accumulates triacylglycerols (TAGs) in lipid droplets under stress conditions, such as nitrogen starvation. TAG biosynthesis occurs mainly at the endoplasmic reticulum (ER) and requires fatty acid (FA) substrates supplied from chloroplasts. How FAs are transferred from chloroplast to ER in microalgae was unknown. We previously reported that an Arabidopsis thaliana ATP-binding cassette (ABC) transporter, AtABCA9, facilitates FA transport at the ER during seed development. Here we identified a gene homologous to AtABCA9 in the C. reinhardtii genome, which we named CrABCA2. Under nitrogen deprivation conditions, CrABCA2 expression was upregulated, and the CrABCA2 protein level also increased. CrABCA2 knockdown lines accumulated less TAGs and CrABCA2 overexpression lines accumulated more TAGs than their untransformed parental lines. Transmission electron microscopy showed that CrABCA2 was localized in swollen ER. These results suggest that CrABCA2 transports substrates for TAG biosynthesis to the ER during nitrogen starvation . Our study provides a potential tool for increasing lipid production in microalgae.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Chlamydomonas reinhardtii/fisiologia , Cloroplastos/metabolismo , Retículo Endoplasmático/metabolismo , Ácidos Graxos/metabolismo , Gotículas Lipídicas/metabolismo , Triglicerídeos/metabolismo , Transportadores de Cassetes de Ligação de ATP/genética , Arabidopsis , Regulação da Expressão Gênica , Metabolismo dos Lipídeos , Microscopia Eletrônica de Transmissão , Mutação/genética , Nitrogênio/metabolismo , Filogenia , Alinhamento de Sequência
7.
Microb Ecol ; 79(3): 576-587, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31463663

RESUMO

Anthropogenic extreme environments are emphasized as interesting sites for the study of evolutionary pathways, biodiversity, and extremophile bioprospection. Organisms that grow under these conditions are usually regarded as extremophiles; however, the extreme novelty of these environments may have favor adaptive radiations of facultative extremophiles. At the Iberian Peninsula, uranium mining operations have rendered highly polluted extreme environments in multiple locations. In this study, we examined the phytoplankton diversity, community structure, and possible determining factors in separate uranium mining-impacted waters. Some of these human-induced extreme environments may be able to sustain indigenous facultative extremophile phytoplankton species, as well as alleged obligate extremophiles. Therefore, we investigated the adaptation capacity of three laboratory strains, two Chlamydomonas reinhardtii and a Dictyosphaerium chlorelloides, to uranium-polluted waters. The biodiversity among the sampled waters was very low, and despite presenting unique taxonomic records, ecological patterns can be identified. The microalgae adaptation experiments indicated a gradient of ecological novelty and different phenomena of adaptation, from acclimation in some waters to non-adaptation in the harshest anthropogenic environment. Certainly, phytoplankton extremophiles might have been often overlooked, and the ability to flourish in extreme environments might be a functional feature in some neutrophilic species. Evolutionary biology and microbial biodiversity can benefit the study of recently evolved systems such as uranium-polluted waters. Moreover, anthropogenic extremophiles can be harnessed for industrial applications.


Assuntos
Clorófitas/fisiologia , Extremófilos/fisiologia , Fitoplâncton/fisiologia , Urânio/análise , Poluentes Radioativos da Água/análise , Biodiversidade , Chlamydomonas reinhardtii/fisiologia , Chlamydomonas reinhardtii/efeitos da radiação , Clorófitas/efeitos da radiação , Extremófilos/efeitos da radiação , Mineração , Fitoplâncton/efeitos da radiação , Portugal , Espanha
8.
Proc Natl Acad Sci U S A ; 117(1): 761-770, 2020 01 07.
Artigo em Inglês | MEDLINE | ID: mdl-31871206

RESUMO

Small RNAs (sRNAs) associate with Argonaute (AGO) proteins in effector complexes, termed RNA-induced silencing complexes (RISCs), which regulate complementary transcripts by translation inhibition and/or RNA degradation. In the unicellular alga Chlamydomonas, several metazoans, and land plants, emerging evidence indicates that polyribosome-associated transcripts can be translationally repressed by RISCs without substantial messenger RNA (mRNA) destabilization. However, the mechanism of translation inhibition in a polyribosomal context is not understood. Here we show that Chlamydomonas VIG1, an ortholog of the Drosophila melanogaster Vasa intronic gene (VIG), is required for this process. VIG1 localizes predominantly in the cytosol and comigrates with monoribosomes and polyribosomes by sucrose density gradient sedimentation. A VIG1-deleted mutant shows hypersensitivity to the translation elongation inhibitor cycloheximide, suggesting that VIG1 may have a nonessential role in ribosome function/structure. Additionally, FLAG-tagged VIG1 copurifies with AGO3 and Dicer-like 3 (DCL3), consistent with it also being a component of the RISC. Indeed, VIG1 is necessary for the repression of sRNA-targeted transcripts at the translational level but is dispensable for cleavage-mediated RNA interference and for the association of the AGO3 effector with polyribosomes or target transcripts. Our results suggest that VIG1 is an ancillary ribosomal component and plays a role in sRNA-mediated translation repression of polyribosomal transcripts.


Assuntos
Chlamydomonas reinhardtii/fisiologia , Proteínas de Plantas/metabolismo , Biossíntese de Proteínas/fisiologia , RNA Interferente Pequeno/metabolismo , Complexo de Inativação Induzido por RNA/metabolismo , Proteínas Argonauta/metabolismo , Cicloeximida/farmacologia , Citosol/metabolismo , Regulação da Expressão Gênica de Plantas , Íntrons/genética , Mutação , Proteínas de Plantas/genética , Plantas Geneticamente Modificadas , Polirribossomos/genética , Polirribossomos/metabolismo , Biossíntese de Proteínas/efeitos dos fármacos , Ribossomos/efeitos dos fármacos , Ribossomos/metabolismo
9.
Phys Rev Lett ; 123(15): 158101, 2019 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-31702314

RESUMO

Microorganismal motility is often characterized by complex responses to environmental physico-chemical stimuli. Although the biological basis of these responses is often not well understood, their exploitation already promises novel avenues to directly control the motion of living active matter at both the individual and collective level. Here we leverage the phototactic ability of the model microalga Chlamydomonas reinhardtii to precisely control the timing and position of localized cell photoaccumulation, leading to the controlled development of isolated bioconvective plumes. This novel form of photobioconvection allows a precise, fast, and reconfigurable control of the spatiotemporal dynamics of the instability and the ensuing global recirculation, which can be activated and stopped in real time. A simple continuum model accounts for the phototactic response of the suspension and demonstrates how the spatiotemporal dynamics of the illumination field can be used as a simple external switch to produce efficient bio mixing.


Assuntos
Chlamydomonas reinhardtii/fisiologia , Modelos Biológicos , Fotobiologia , Processos Fototróficos
10.
Cells ; 8(10)2019 10 11.
Artigo em Inglês | MEDLINE | ID: mdl-31614608

RESUMO

Temperature is one of the key factors affecting growth and division of algal cells. High temperature inhibits the cell cycle in Chlamydomonas reinhardtii. At 39 °C, nuclear and cellular divisions in synchronized cultures were blocked completely, while DNA replication was partly affected. In contrast, growth (cell volume, dry matter, total protein, and RNA) remained unaffected, and starch accumulated at very high levels. The cell cycle arrest could be removed by transfer to 30 °C, but a full recovery occurred only in cultures cultivated up to 14 h at 39 °C. Thereafter, individual cell cycle processes began to be affected in sequence; daughter cell release, cell division, and DNA replication. Cell cycle arrest was accompanied by high mitotic cyclindependent kinase activity that decreased after completion of nuclear and cellular division following transfer to 30 °C. Cell cycle arrest was, therefore, not caused by a lack of cyclin-dependent kinase activity but rather a blockage in downstream processes.


Assuntos
Técnicas de Cultura de Células/métodos , Pontos de Checagem do Ciclo Celular , Chlamydomonas reinhardtii/citologia , Proteínas de Algas/metabolismo , Chlamydomonas reinhardtii/fisiologia , Quinases Ciclina-Dependentes/metabolismo , Regulação para Baixo , Regulação da Expressão Gênica de Plantas , Temperatura Alta , Estresse Fisiológico
11.
Biophys J ; 117(8): 1508-1513, 2019 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-31586523

RESUMO

Phototaxis is one of the most fundamental stimulus-response behaviors in biology wherein motile microorganisms sense light gradients to swim toward the light source. Apart from single-cell survival and growth, it plays a major role at the global scale of aquatic ecosystems and bioreactors. We study phototaxis of single-celled algae Chlamydomonas reinhardtii as a function of cell number density and light stimulus using high spatiotemporal video microscopy. Surprisingly, the phototactic efficiency has a minimum at a well-defined number density, for a given light gradient, above which the phototaxis behavior of a collection of cells can even exceed the performance obtainable from single isolated cells. We show that the origin of enhancement of performance above the critical concentration lies in the slowing down of the cells, which enables them to sense light more effectively. We also show that this steady-state phenomenology is well captured by modeling the phototactic response as a density-dependent torque acting on an active Brownian particle.


Assuntos
Chlamydomonas reinhardtii/fisiologia , Fototaxia , Fenômenos Biomecânicos , Análise de Célula Única
12.
Cells ; 8(10)2019 09 28.
Artigo em Inglês | MEDLINE | ID: mdl-31569396

RESUMO

The target of rapamycin (TOR) kinase is a master metabolic regulator with roles in nutritional sensing, protein translation, and autophagy. In Chlamydomonas reinhardtii, a unicellular green alga, TOR has been linked to the regulation of increased triacylglycerol (TAG) accumulation, suggesting that TOR or a downstream target(s) is responsible for the elusive "lipid switch" in control of increasing TAG accumulation under nutrient limitation. However, while TOR has been well characterized in mammalian systems, it is still poorly understood in photosynthetic systems, and little work has been done to show the role of oxidative signaling in TOR regulation. In this study, the TOR inhibitor AZD8055 was used to relate reversible thiol oxidation to the physiological changes seen under TOR inhibition, including increased TAG content. Using oxidized cysteine resin-assisted capture enrichment coupled with label-free quantitative proteomics, 401 proteins were determined to have significant changes in oxidation following TOR inhibition. These oxidative changes mirrored characterized physiological modifications, supporting the role of reversible thiol oxidation in TOR regulation of TAG production, protein translation, carbohydrate catabolism, and photosynthesis through the use of reversible thiol oxidation. The delineation of redox-controlled proteins under TOR inhibition provides a framework for further characterization of the TOR pathway in photosynthetic eukaryotes.


Assuntos
Chlamydomonas reinhardtii/fisiologia , Cisteína/química , Morfolinas/farmacologia , Serina-Treonina Quinases TOR/metabolismo , Cromatografia Líquida , Oxirredução/efeitos dos fármacos , Fotossíntese/efeitos dos fármacos , Proteínas de Plantas/metabolismo , Proteômica/métodos , Transdução de Sinais/efeitos dos fármacos , Serina-Treonina Quinases TOR/antagonistas & inibidores , Espectrometria de Massas em Tandem , Triglicerídeos/metabolismo
13.
Sci Rep ; 9(1): 12063, 2019 08 19.
Artigo em Inglês | MEDLINE | ID: mdl-31427663

RESUMO

The phytohormone abscisic acid (ABA) plays a role in stresses that alter plant water status and may also regulate root gravitropism and hydrotropism. ABA also exists in the aquatic algal progenitors of land plants, but other than its involvement in stress responses, its physiological role in these microorganisms remains elusive. We show that exogenous ABA significantly altered the HCO3- uptake of Chamydomonas reinhardtii in a light-intensity-dependent manner. In high light ABA enhanced HCO3- uptake, while under low light uptake was diminished. In the dark, ABA induced a negative geotropic movement of the algae to an extent dependent on the time of sampling during the light/dark cycle. The algae also showed a differential, light-dependent directional taxis response to a fixed ABA source, moving horizontally towards the source in the light and away in the dark. We conclude that light and ABA signal competitively in order for algae to position themselves in the water column to minimise photo-oxidative stress and optimise photosynthetic efficiency. We suggest that the development of this response mechanism in motile algae may have been an important step in the evolution of terrestrial plants and that its retention therein strongly implicates ABA in the regulation of their relevant tropisms.


Assuntos
Ácido Abscísico/metabolismo , Chlamydomonas reinhardtii/metabolismo , Gravitropismo/fisiologia , Reguladores de Crescimento de Planta/metabolismo , Arabidopsis/metabolismo , Arabidopsis/fisiologia , Chlamydomonas reinhardtii/fisiologia , Clorófitas/metabolismo , Clorófitas/fisiologia , Luz , Fotoperíodo , Transdução de Sinais/genética , Estresse Fisiológico/fisiologia , Água/química
14.
J Evol Biol ; 32(11): 1252-1261, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31430421

RESUMO

The explanation for the continued existence of sex, despite its many costs, remains one of the major challenges of evolutionary biology. Previous experimental studies have demonstrated that sex increases the rate of adaptation in novel environments relative to asexual reproduction. Whereas these studies have investigated the impact of sex on adaptation to stressful abiotic environments, the potential for biotic interactions to influence this advantage of sex has been largely ignored. Species rarely exist in isolation in natural conditions, so the impact of sex on adaptation to a stressful abiotic environment may be altered by the interactions between coexisting species. To investigate the interplay of sex and competition on adaptation to deteriorating conditions, we allowed populations of the unicellular alga (Chlamydomonas reinhardtii) to evolve in an environment to which they were initially poorly adapted. We manipulated both their mode of reproduction and the presence of a competitor, and monitored population size and proportion of evolutionary rescue events for each mode of reproduction. The results indicate that sex may be the beneficial strategy in the presence of the competitor. Sexual populations had highest probability of evolutionary rescue irrespective of the presence of the competitor. The overall advantage of sex was also manifested through higher level of adaptedness of survived sexual populations relative to asexual populations. Since competitive interactions are commonplace in nature, one of the explanations for the maintenance of sex by natural selection may be the increased rate of adaptation of sexual populations both in the presence and absence of competitors.


Assuntos
Evolução Biológica , Chlamydomonas reinhardtii/genética , Chlamydomonas reinhardtii/fisiologia , Reprodução/genética , Reprodução/fisiologia , Adaptação Fisiológica/genética , Adaptação Fisiológica/fisiologia , Animais , Salinidade , Tolerância ao Sal/genética , Tolerância ao Sal/fisiologia
15.
Proc Biol Sci ; 286(1909): 20191491, 2019 08 28.
Artigo em Inglês | MEDLINE | ID: mdl-31431166

RESUMO

Pyruvate : ferredoxin oxidoreductase (PFO) and iron only hydrogenase ([Fe]-HYD) are common enzymes among eukaryotic microbes that inhabit anaerobic niches. Their function is to maintain redox balance by donating electrons from food oxidation via ferredoxin (Fd) to protons, generating H2 as a waste product. Operating in series, they constitute a soluble electron transport chain of one-electron transfers between FeS clusters. They fulfil the same function-redox balance-served by two electron-transfers in the NADH- and O2-dependent respiratory chains of mitochondria. Although they possess O2-sensitive FeS clusters, PFO, Fd and [Fe]-HYD are also present among numerous algae that produce O2. The evolutionary persistence of these enzymes among eukaryotic aerobes is traditionally explained as adaptation to facultative anaerobic growth. Here, we show that algae express enzymes of anaerobic energy metabolism at ambient O2 levels (21% v/v), Chlamydomonas reinhardtii expresses them with diurnal regulation. High O2 environments arose on Earth only approximately 450 million years ago. Gene presence/absence and gene expression data indicate that during the transition to high O2 environments and terrestrialization, diverse algal lineages retained enzymes of Fd-dependent one-electron-based redox balance, while the land plant and land animal lineages underwent irreversible specialization to redox balance involving the O2-insensitive two-electron carrier NADH.


Assuntos
Adaptação Fisiológica/fisiologia , Chlamydomonas reinhardtii/fisiologia , Ferredoxinas/metabolismo , NAD/metabolismo , Anaerobiose , Animais , Transporte de Elétrons , Metabolismo Energético , Hidrogenase , Proteínas com Ferro-Enxofre , Oxigênio/metabolismo
16.
Mar Drugs ; 17(8)2019 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-31434347

RESUMO

Microalgal lipids are a source of valuable nutritional ingredients in biotechnological industries, and are precursors to biodiesel production. Here, the effects of salt-induced stresses, including NaCl, KCl, and LiCl stresses, on the production of lipid in green microalga Chlamydomonas reinhardtii (137c) were investigated. NaCl stress dramatically increased saturated fatty acids (SFAs), which accounted for 70.2% of the fatty acid methyl ester (FAMEs) under stress. In contrary, KCl stress led to a slight increase in SFAs (47.05%) with the remaining being polyunsaturated fatty acids (PUFAs) (45.77%). RT-PCR analysis revealed that the genes involved in FA biosynthesis, such as PDH2, ACCase, MAT and KAS2, were up-regulated by NaCl-induced stress. Conversely, the genes responsible for the Kennedy pathway were suppressed. The alteration of FA homeostasis was further assessed by overexpressing MAT, the enzyme responsible for the production of malonyl-ACP, a key building block for FA biosynthesis, in the cyanobacterium Synechococcus elongatus PCC 7942. Intracellular FA composition was affected, with a predominant synthesis of SFAs in transformed cells. Owing to the diversity and relative abundance of SFAs, monounsaturated fatty acid (MUFAs) and PUFAs enable the feasibility of using microorganisms as a source of microalgal lipids or valuable nutritional ingredients; salt-induced stress and expression of MAT are useful in providing precursors for enhanced lipid production.


Assuntos
Chlamydomonas reinhardtii/metabolismo , Chlamydomonas reinhardtii/fisiologia , Lipídeos/biossíntese , Estresse Salino/fisiologia , Chlamydomonas reinhardtii/citologia , Ácidos Graxos/metabolismo , Ácidos Graxos Insaturados/metabolismo , Metabolismo dos Lipídeos , Microalgas/metabolismo , Cloreto de Sódio
17.
Proc Natl Acad Sci U S A ; 116(30): 14852-14861, 2019 07 23.
Artigo em Inglês | MEDLINE | ID: mdl-31292259

RESUMO

The dynamics of ecological change following a major perturbation, known as succession, are influenced by random processes. Direct quantitation of the degree of contingency in succession requires chronological study of replicate ecosystems. We previously found that population dynamics in carefully controlled, replicated synthetic microbial ecosystems were strongly deterministic over several months. Here, we present simplified, two-species microbial ecosystems consisting of algae and ciliates, imaged in toto at single-cell resolution with fluorescence microscopy over a period of 1 to 2 weeks. To directly study succession in these ecosystems, we deliberately varied the initial cell abundances over replicates and quantified the ensuing dynamics. The distribution of abundance trajectories rapidly converged to a nearly deterministic path, with small fluctuations, despite variations in initial conditions, environmental perturbations, and intrinsic noise, indicative of homeorhesis. Homeorhesis was also observed for certain phenotypic variables, such as partitioning of the ciliates into distinct size classes and clumping of the algae. Although the mechanism of homeorhesis observed in these synthetic ecosystems remains to be elucidated, it is clear that it must emerge from the ways each species controls its own internal states, with respect to a diverse set of environmental conditions and ecological interactions.


Assuntos
Chlamydomonas reinhardtii/fisiologia , Ecossistema , Homeostase , Tetrahymena thermophila/fisiologia , Simbiose
18.
Sci Rep ; 9(1): 9856, 2019 07 08.
Artigo em Inglês | MEDLINE | ID: mdl-31285472

RESUMO

Autophagy is a self-degradation system wherein cellular materials are recycled. Although autophagy has been extensively studied in yeast and mammalian systems, integrated stress responses in microalgae remain poorly understood. Accordingly, we carried out a comparative study on the oxidative stress responses of Chlamydomonas reinhardtii wild-type and a starchless (sta6) mutant previously shown to accumulate high lipid content under adverse conditions. To our surprise, the sta6 mutant exhibited significantly higher levels of lipid peroxidation in the same growth conditions compared to controls. The sta6 mutant was more sensitive to oxidative stress induced by H2O2, whereas the wild-type was relatively more resistant. In addition, significantly up-regulated autophagy-related factors including ATG1, ATG101, and ATG8 were maintained in the sta6 mutant regardless of nitrogen availability. Also, the sta6 mutant exhibited relatively higher ATG8 protein level compared to wild-type under non-stress condition, and quickly reached a saturation point of autophagy when H2O2 was applied. Our results indicate that, in addition to the impact of carbon allocation, the increased lipid phenotype of the sta6 mutant may result from alterations in the cellular oxidative state, which in turn activates autophagy to clean up oxidatively damaged components and fuel lipid production.


Assuntos
Autofagia/fisiologia , Chlamydomonas reinhardtii/metabolismo , Chlamydomonas reinhardtii/fisiologia , Estresse Oxidativo/fisiologia , Amido/biossíntese , Metabolismo dos Carboidratos/fisiologia , Carbono/metabolismo , Peroxidação de Lipídeos/fisiologia , Lipídeos/fisiologia , Nitrogênio/metabolismo , Oxirredução , Fenótipo , Regulação para Cima/fisiologia
20.
Plant Cell Physiol ; 60(10): 2167-2179, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31198969

RESUMO

Monodehydroascorbate reductase (MDAR; EC 1.6.5.4) is one of the key enzymes in the conversion of oxidized ascorbate (AsA) back to reduced AsA in plants. This study investigated the role of MDAR in the tolerance of Chlamydomonas reinhardtii P.A. Dangeard to photooxidative stress by overexpression and downregulation of the CrMDAR1 gene. For overexpression of CrMDAR1 driven by a HSP70A:RBCS2 fusion promoter, the cells survived under very high-intensity light stress (VHL, 1,800 µmol�m-2�s-1), while the survival of CC-400 and vector only control (vector without insert) cells decreased for 1.5 h under VHL stress. VHL increased lipid peroxidation of CC-400 but did not alter lipid peroxidation in CrMDAR1 overexpression lines. Additionally, overexpression of CrMDAR1 showed an increase in viability, CrMDAR1 transcript abundance, enzyme activity and the AsA: dehydroascorbate (DHA) ratio. Next, MDAR was downregulated to examine the essential role of MDAR under high light condition (HL, 1,400 µmol�m-2�s-1). The CrMDAR1 knockdown amiRNA line exhibited a low MDAR transcript abundance and enzyme activity and the survival decreased under HL conditions. Additionally, HL illumination decreased CrMDAR1 transcript abundance, enzyme activity and AsA:DHA ratio of CrMDAR1-downregulation amiRNA lines. Methyl viologen (an O2�- generator), H2O2 and NaCl treatment could induce an increase in CrMDAR1 transcript level. It represents reactive oxygen species are one of the factor inducing CrMDAR1 gene expression. In conclusion, MDAR plays a role in the tolerance of Chlamydomonas cells to photooxidative stress.


Assuntos
Ácido Ascórbico/metabolismo , Chlamydomonas reinhardtii/enzimologia , NADH NADPH Oxirredutases/metabolismo , Estresse Fisiológico , Chlamydomonas reinhardtii/genética , Chlamydomonas reinhardtii/fisiologia , Chlamydomonas reinhardtii/efeitos da radiação , Regulação para Baixo , Regulação da Expressão Gênica de Plantas , Peróxido de Hidrogênio/farmacologia , Luz , Peroxidação de Lipídeos , NADH NADPH Oxirredutases/genética , Estresse Oxidativo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Regiões Promotoras Genéticas/genética , Cloreto de Sódio/farmacologia
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