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Development of a CRISPR/Cas gene editing technique for the coccolithophore Chrysotila carterae
(2024)
Nils-Hendrik Grohmann beschäftigt sich mit dem noch andauernden Stärkungsprozess der UN-Menschenrechtsvertragsorgane. Er analysiert, welche rechtlichen Befugnisse die Ausschüsse haben, ob sie von sich aus Vorschläge einbringen können und inwieweit sie ihre Verfahrensweisen bisher aufeinander abgestimmt haben. Ein weiterer Schwerpunkt liegt auf der Zusammenarbeit zwischen den verschiedenen Ausschüssen und der Frage, welche Rolle das Treffen der Vorsitzenden bei der Stärkung spielen kann.
This dissertation examines the lack of clarity in the scientific literature regarding gender and negotiation performance. It is often claimed that men negotiate better than women, yet it is simultaneously emphasized that results strongly depend on context. Through the use of qualitative methods such as content analysis and critical mixed-methods review, the research question: "Are women truly inferior negotiators compared to men?" is addressed. The study comprises a descriptive and an interpretive part. The descriptive section illuminates various interpretations of gender-specific negotiation theory among citing authors, with 67% arguing for a general superiority of men. However, given the high variance in gender-specific differences, the focus should instead be on the context-dependency of negotiation performance. Generalized statements can be made within contexts, but not across them. In the interpretive section, several factors contributing to this misinterpretation are highlighted, including discrepancies in the definition of negotiation performance and distortions in research communication.. From a scientific perspective, this study underscores the need for a nuanced sociological analysis and warns against the one-sided acceptance of inaccurate scientific interpretations. From a practical standpoint, it amplifies the voices of women affected by biased research paradigms. Overall, the dissertation clarifies the theory of gender-specific negotiation performance and advocates for the elimination of biases in scientific discourse.
Electricity production contributes to a significant share of greenhouse gas emissions in Europe and is thus an important driver of climate change. To fulfil the Paris Agreement, the European Union (EU) needs a rapid transition to a fully decarbonised power production system. Presumably, such a system will be largely based on renewables. So far, many EU countries have supported a shift towards renewables such as solar and wind power using support schemes, but the economic and political context is changing. Renewables are now cheaper than ever before and have become cost-competitive with conventional technologies. Therefore, European policymakers are striving to better integrate renewables into a competitive market and to increase the cost-effectiveness of the expansion of renewables. The first step was to replace previous fixed-price schemes with competitive auctions. In a second step, these auctions have become more technology-open. Finally, some governments may phase out any support for renewables and fully expose them to the competitive power market.
However, such policy changes may be at odds with the need to rapidly expand renewables and meet national targets due to market characteristics and investors’ risk perception. Without support, price risks are higher, and it may be difficult to meet an investor’s income expectations. Furthermore, policy changes across different countries could have unexpected effects if power markets are interconnected and investors able to shift their investments. Finally, in multi-technology auctions, technologies may dominate, which can be a risk for long-term power system reliability. Therefore, in my thesis, I explore the effects of phasing out support policies for renewables, of coordinating these phase-outs across countries, and of using multi-technology designs. I expand the public policy literature about investment behaviour and policy design as well as policy change and coordination, and I further develop an agent-based model.
The main questions of my thesis are what the cost and deployment effects of gradually exposing renewables to market forces would be and how coordination between countries affects investors’ decisions and market prices.. In my three contributions to the academic literature, I use different methods and come to the following results. In the first contribution, I use a conjoint analysis and market simulation to evaluate the effects of phasing out support or reintroducing feed-in tariffs from the perspective of investors. I find that a phase-out leads to investment shifts, either to other still-supported technologies or to other countries that continue to offer support. I conclude that the coordination of policy changes avoids such shifts.. In the second contribution, I integrate the empirically-derived preferences from the first contribution in to an agent-based power system model of two countries to simulate the effects of ending auctions for renewables. I find that this slows the energy transition, and that cross-border effects are relevant. Consequently, continued support is necessary to meet the national renewables targets. In the third contribution, I analyse the outcome of past multi-technology auctions using descriptive statistics, regression analysis as well as case study comparisons. I find that the outcomes are skewed towards single technologies. This cannot be explained by individual design elements of the auctions, but rather results from context-specific and country-specific characteristics. Based on this, I discuss potential implications for long-term power system reliability.
The main conclusions of my thesis are that a complete phase-out of renewables support would slow down the energy transition and thus jeopardize climate targets, and that multi-technology auctions may pose a risk for some countries, especially those that cannot regulate an unbalanced power plant portfolio in the long term. If policymakers decide to continue supporting renewables, they may consider adopting technology-specific auctions to better steer their portfolio. In contrast, if policymakers still want to phase out support, they should coordinate these policy changes with other countries. Otherwise, overall transition costs can be higher, because investment decisions shift to still-supported but more expensive technologies.
Cross-sectional associations of dietary biomarker patterns with health and nutritional status
(2024)
Aging is associated with bone loss, which can lead to osteoporosis and high fracture risk. This coincides with the enhanced formation of bone marrow adipose tissue (BMAT), suggesting a negative effect of bone marrow adipocytes on skeletal health. Increased BMAT formation is also observed in pathologies such as obesity, type 2 diabetes and osteoporosis. However, a subset of bone marrow adipocytes forming the constitutive BMAT (cBMAT), arise early in life in the distal skeleton, contain high levels of unsaturated fatty acids and are thought to provide a physiological function. Regulated BMAT (rBMAT) forms during aging and obesity in proximal regions of the bone and contain a large proportion of saturated fatty acids. Paradoxically, BMAT accumulation is also enhanced during caloric restriction (CR), a life-span extending dietary intervention. This indicates, that different types of BMAT can form in response to opposing nutritional stimuli with potentially different functions.
To this end, two types of nutritional interventions, CR and high fat diet (HFD), that are both described to induce BMAT accumulation were carried out. CR markedly increased BMAT formation in the proximal tibia and led to a higher proportion of unsaturated fatty acids, making it similar to the physiological cBMAT. Additionally, proximal and diaphyseal tibia regions displayed higher adiponectin expression. In aged mice, CR was associated with an improved trabecular bone structure. Taken together, these findings demonstrate, that the type of BMAT that forms during CR might provide beneficial effects for local bone stem/progenitor cells and metabolic health. The HFD intervention performed in this thesis showed no effect on BMAT accumulation and bone microstructure. RNA Seq analysis revealed alterations in the composition of the collagen-containing extracellular matrix (ECM).
In order to investigate the effects of glucose homeostasis on osteogenesis, differentiation capacity of immortalized multipotent mesenchymal stromal cells (MSCs) and osteochondrogenic progenitor cells (OPCs) was analyzed. Insulin improved differentiation in both cell types, however, combination of with a high glucose concentration led to an impaired mineralization of the ECM. In the MSCs, this was accompanied by the formation of adipocytes, indicating negative effects of the adipocytes formed during hyperglycemic conditions on mineralization processes. However, the altered mineralization pattern and structure of the ECM was also observed in OPCs, which did not form any adipocytes, suggesting further negative effects of a hyperglycemic environment on osteogenic differentiation.
In summary, the work provided in this thesis demonstrated that differentiation commitment of bone-resident stem cells can be altered through nutrient availability, specifically glucose. Surprisingly, both high nutrient supply, e.g. the hyperglycemic cell culture conditions, and low nutrient supply, e.g. CR, can induce adipogenic differentiation. However, while CR-induced adipocyte formation was associated with improved trabecular bone structure, adipocyte formation in a hyperglycemic cell-culture environment hampered mineralization. This thesis provides further evidence for the existence of different types of BMAT with specific functions.
The plant cell wall plays several crucial roles during plant development with its integrity acting as key signalling component for growth regulation during biotic and abiotic stresses. Cellulose microfibrils, the principal load-bearing components is the major component of the primary cell wall, whose synthesis is mediated by microtubule-associated CELLULOSE SYNTHASE (CESA) COMPLEXES (CSC). Previous studies have shown that CSC interacting proteins COMPANION OF CELLULOSE SYNTHASE (CC) facilitate sustained cellulose synthesis during salt stress by promoting repolymerization of cortical microtubules. However, our understanding of cellulose synthesis during salt stress remains incomplete.
In this study, a pull-down of CC1 protein led to the identification of a novel interactor, termed LEA-like. Phylogenetic analysis revealed that LEA-like belongs to the LATE EMBRYOGENESIS ABUNDANT (LEA) protein family, specifically to the LEA_2 subgroup, showing a close relationship with the CC proteins. Roots of the double mutants lea-like and its closest homolog emb3135 exhibited hypersensitivity when grown on cellulose synthesis inhibitors. Further analysis of higher-order mutants of lea-like, emb3135, and cesa6 demonstrated a genetic interaction between them indicating a significant role in cellulose synthesis.
Live-cell imaging revealed that both LEA-like and EMB3135 migrated with the CSC at the plasma membrane along microtubule tracks in control and oryzalin-treated conditions which destabilize microtubules, suggesting a tight interaction. Investigation of fluorescently labeled lines of different domains of the LEA-like protein revealed that the N-terminal cytosolic domain of LEA-like colocalizes with microtubules, suggesting a physical association between the two.
Considering the established role of LEA proteins in abiotic stress tolerance, we performed phenotypic analysis of the mutant under various stresses. Growth of double mutants of lea-like and emb3135 on NaCl containing media resulted in swelling of root cell indicating a putative role in salt stress tolerance. Supportive of this the quadruple mutant, lacking LEA-like, EMB3135, CC1, and CC2 proteins, exhibited a severe root growth defect on NaCl media compared to control conditions. Live-cell imaging revealed that under salt stress, the LEA-like protein forms aggregates in the plasma membrane.
In conclusion, this study has unveiled two novel interactors of the CSC that act with the CC proteins that regulate plant growth in response to salt stress providing new insights into the intricate regulation of cellulose synthesis, particularly under such conditions.
The trace elements copper, iron, manganese, selenium and zinc are essential micronutrients involved in various cellular processes, all with different responsibilities. Based on that importance, their concentrations are tightly regulated in mammalian organisms. The maintenance of those levels is termed trace element homeostasis and mediated by a combination of processes regulating absorption, cellular and systemic transport mechanisms, storage and effector proteins as well as excretion. Due to their chemical properties, some functions of trace elements overlap, as seen in antioxidative defence, for example, comprising an expansive spectrum of antioxidative proteins and molecules. Simultaneously, the same is true for regulatory mechanisms, causing trace elements to influence each other’s homeostases. To mimic physiological conditions, trace elements should therefore not be evaluated separately but considered in parallel. While many of these homeostatic mechanisms are well-studied, for some elements new pathways are still discovered. Additionally, the connections between dietary trace element intake, trace element status and health are not fully unraveled, yet. With current demographic developments, also the influence of ageing as well as of certain pathological conditions is of increasing interest. Here, the TraceAge research unit was initiated, aiming to elucidate the homeostases of and interactions between essential trace elements in healthy and diseased elderly. While human cohort studies can offer insights into trace element profiles, also in vivo model organisms are used to identify underlying molecular mechanisms. This is achieved by a set of feeding studies including mice of various age groups receiving diets of reduced trace element content. To account for cognitive deterioration observed with ageing, neurodegenerative diseases, as well as genetic mutations triggering imbalances in cerebral trace element concentrations, one TraceAge work package focuses on trace elements in the murine brain, specifically the cerebellum. In that context, concentrations of the five essential trace elements of interest, copper, iron, manganese, selenium and zinc, were quantified via inductively coupled plasma-tandem mass spectrometry, revealing differences in priority of trace element homeostases between brain and liver. Upon moderate reduction of dietary trace element supply, cerebellar concentrations of copper and manganese deviated from those in adequately supplied animals. By further reduction of dietary trace element contents, also concentrations of cerebellar iron and selenium were affected, but not as strong as observed in liver tissue. In contrast, zinc concentrations remained stable. Investigation of aged mice revealed cerebellar accumulation of copper and iron, possibly contributing to oxidative stress on account of their redox properties. Oxidative stress affects a multitude of cellular components and processes, among them, next to proteins and lipids, also the DNA. Direct insults impairing its integrity are of relevance here, but also indirect effects, mediated by the machinery ensuring genomic stability and its functionality. The system includes the DNA damage response, comprising detection of endogenous and exogenous DNA lesions, decision on subsequent cell fate and enabling DNA repair, which presents another pillar of genomic stability maintenance. Also in proteins of this machinery, trace elements act as cofactors, shaping the hypothesis of impaired genomic stability maintenance under conditions of disturbed trace element homeostasis. To investigate this hypothesis, a variety of approaches was used, applying OECD guidelines Organisation for Economic Co-operation and Development, adapting existing protocols for use in cerebellum tissue and establishing new methods. In order to assess the impact of age and dietary trace element depletion on selected endpoints estimating genomic instability, DNA damage and DNA repair were investigated. DNA damage analysis, in particular of DNA strand breaks and oxidatively modified DNA bases, revealed stable physiological levels which were neither affected by age nor trace element supply. To examine whether this is a result of increased repair rates, two steps characteristic for base excision repair, namely DNA incision and ligation activity, were studied. DNA glycosylases and DNA ligases were not reduced in their activity by age or trace element depletion, either. Also on the level of gene expression, major proteins involved in genomic stability maintenance were analysed, mirroring results obtained from protein studies. To conclude, the present work describes homeostatic regulation of trace elements in the brain, which, in absence of genetic mutations, is able to retain physiological levels even under conditions of reduced trace element supply to a certain extent. This is reflected by functionality of genomic stability maintenance mechanisms, illuminating the prioritization of the brain as vital organ.
The inclusion of exotic germplasm serves as a crucial means to enhance allelic and
consequently phenotypic diversity in inbred crop species. Such species have experienced a reduction in diversity due to artificial selection focused on a limited set of traits. The natural biodiversity within ecosystems presents an opportunity to explore various traits influencing plant survival, reproductive fitness and yield potential. In agricultural research, the study of wild species closely related to cultivated plants serves as a means to comprehend the genetic foundations of past domestication events and the polymorphisms essential for future breeding efforts to develop superior varieties. In order to examine the metabolic composition, pinpoint quantitative trait loci (QTL) and facilitate their resolution an extensive large-scale analysis of metabolic QTL (mQTL) was conducted on tomato backcross inbred lines (BILs) derived from a cross between the wild species S. pennellii (5240) incorporated into the background of S. lycopersicum cv. LEA determinate inbred which can be grown in open fields and cv. TOP indeterminate which can be grown in greenhouse conditions. A large number of mQTL associated with primary secondary and lipid metabolism in fruit were identified across the two BIL populations. Epistasis, the interactions between genes at different loci, has been an interest in molecular and quantitative genetics for many decades. The study of epistasis requires the analysis of very large populations with multiple independent genotypes that carry specific genomic regions. In order to understand the genetic basis of tomato fruit metabolism, I extended the work to investigate epistatic interactions of the genomic regions. In addition, two candidate genes were identified through quantitative trait loci underlying fruit-specific sucrose and jasmonic acid derivatives. Finally, in this study, I assessed the genetic framework of fruit metabolic traits with a high level of detail, utilizing the newly created Solanum pennellii (5240) backcrossed introgression lines (n=3000). This investigation resulted in the discovery of promising candidate loci associated with significant fruit quality traits, including those to the abundance of glutamic acid and aspartic acid crucial elements contributing to the development of acidity and flavors.
Wars and the world
(2024)
This book offers a descriptive analysis of the Soviet/Russian wars in Afghanistan, Chechnya, and Georgia, as well as an in-depth exploration of the ways in which these wars are framed in the collective consciousness created by global popular culture. Russian and Western modalities of remembrance have been, and remain, engaged in a world war that takes place (not exclusively, but intensively) on the level of popular culture. The action/reaction dynamic, confrontational narratives and othering between the two "camps" never ceased. The Cold War, in many ways and contrary to the views of many others who hoped for the end of history, never really ended.
Diglossic translanguaging
(2024)
This book examines how German-speaking Jews living in Berlin make sense and make use of their multilingual repertoire. With a focus on lexical variation, the book demonstrates how speakers integrate Yiddish and Hebrew elements into German for indexing belonging and for positioning themselves within the Jewish community. Linguistic choices are shaped by language ideologies (e.g., authenticity, prescriptivism, nostalgia). Speakers translanguage when using their multilingual repertoire, but do so in a diglossic way, using elements from different languages for specific domains
The biosecurity individual
(2024)
Discoveries in biomedicine and biotechnology, especially in diagnostics, have made prevention and (self)surveillance increasingly important in the context of health practices. Frederike Offizier offers a cultural critique of the intersection between health, security and identity, and explores how the focus on risk and security changes our understanding of health and transforms our relationship to our bodies. Analyzing a wide variety of texts, from life writing to fiction, she offers a critical intervention on how this shift in the medical gaze produces new paradigms of difference and new biomedically facilitated identities: biosecurity individuals.
How do the rights of same-sex couples have to be ensured by states, and which kind of environmental obligations are induced by the right to life and to personal integrity? Questions as diverse and far-reaching as these are regularly dealt with by the Inter-American Court of Human Rights in its advisory function. This book is the first comprehensive, non-Spanish-written treatise on the advisory function of this Court. It analyzes the scope of the Court's advisory jurisdiction and its procedural practice in comparison with that of other international courts. Moreover, the legal effects of the Court’s advisory opinions and the question when the Court should better reject a request for an advisory opinion are examined.
Phobic cosmopolitanism
(2024)
The order of destruction
(2024)
This book studies sugarcane monoculture, the dominant form of cultivation in the colonial Caribbean, in the later 1600s and 1700s up to the Haitian Revolution. Researching travel literature, plantation manuals, Georgic poetry, letters, and political proclamations, this book interprets texts by Richard Ligon, Henry Drax, James Grainger, Janet Schaw, and Toussaint Louverture. As the first extended investigation into its topic, this book reads colonial Caribbean monoculture as the conjunction of racial capitalism and agrarian capitalism in the tropics. Its eco-Marxist perspective highlights the dual exploitation of the soil and of enslaved agricultural producers under the plantation regime, thereby extending Marxist analysis to the early colonial Caribbean. By focusing on textual form (in literary and non-literary texts alike), this study discloses the bearing of monoculture on contemporary writers' thoughts. In the process, it emphasizes the significance of a literary tradition that, despite its ideological importance, is frequently neglected in (postcolonial) literary studies and the environmental humanities. Located at a crossroads of disciplines and perspectives, this study will be of interest to literary critics and historians working in the early Americas, to students and scholars of agriculture, colonialism, and (racial) capitalism, to those working in the environmental humanities, and to Marxist academics. It will be of great interest to scholars and researchers of language and literature, post-colonial studies, cultural studies, diaspora studies, and the Global South studies
Carbohydrates play a vital role in all living organisms; serving as a cornerstone in primary metabolism through the release of energy from their hydrolysis and subsequent re-utilization (Apriyanto et al., 2022). Starch is the principal carbohydrate reserve in plants, providing essential energy for plant growth. Furthermore, starch serves as a significant carbohydrate source in the human diet. Beyond its nutritional value, starch has extensive industrial application associated with many aspects of human society, such as feed, pharmacy, textiles, and the production of biodegradable plastics. Understanding the mechanisms underlying starch metabolism in plants carries multifaceted benefits. Not only does it contribute to increasing crop yield and refining grain quality, but also can improve the efficiency of industrial applications.
Starch in plants is categorized into two classes based on their location and function: transitory starch and storage starch. Transitory starch is produced in chloroplasts of autotrophic tissues/organs, such as leaves. It is synthesized during the day and degraded during the night. Storage starch is synthesized in heterotrophic tissues/organs, such as endosperm, roots and tubers, which is utilized for plant reproduction and industrial application in human life. Most studies aiming to comprehend starch metabolism of Arabidopsis thaliana primarily focus on transitory starch.
Starch is stored as granular form in chloroplast and amyloplast. The parameters of starch granules, including size, morphology, and quantity per chloroplast serve as indicators of starch metabolism status. However, the understanding of their regulatory mechanism is still incomplete. In this research, I initially employed a simple and adapted method based on laser confocal scanning microscopy (LCSM) to observe size, morphology and quantity of starch granules within chloroplasts in Arabidopsis thaliana in vivo. This method facilitated a rapid and versatile analysis of starch granule parameters across numerous samples. Utilizing this approach, I compared starch granule number per chloroplast between mesophyll cells and guard cells in both wild type plants (Col-0) and several starch related mutants. The results revealed that the granule number is distinct between mesophyll cells and guard cells, even within the same genetic background, suggesting that guard cells operate a unique regulatory mechanism of starch granule number.
Subsequently, I redirected my attention toward examining starch morphology. Through microscopy analyses, I observed a gradual alteration in starch granule morphology in certain mutants during leaf aging. Specifically, in mutants such as sex1-8 and dpe2phs1ss4, there was a progressive alteration in starch granule morphology over time. Conversely, in Col-0 and ss4 mutant, these morphological alterations were not evident. This discovery suggests a new perspective to understand the development of starch morphology.
Further investigation revealed that mutants lacking either Disproportionating enzyme 2 (DPE2) or MALTOSE-EXCESS 1 (MEX1) exhibited gradual alterations in starch morphology with leaf aging. Notably, the most severe effects on starch morphology occurred in double mutants lacking either DPE2 or MEX1 in conjunction with a lack of starch synthase 4 (SS4). In these mutations, a transformation of the starch granule morphology from the typical discoid morphology to oval and eventually to a spherical shape.
To investigate the changes in the internal structure of starch during this alteration, I analyzed the chain length distribution (CLD) of the amylopectin of young, intermediate and old leaves of the mutants. Throughout starch granule development, I found an increased presence of short glucan chains within the granules, particularly evident in dpe2ss4 and mex1ss4 mutants, as well as their parental single mutants. Notably, the single mutant ss4 also showed an affected granule morphology, albeit not influenced by leaf aging..
The CLD pattern of the amylopectin reflects an integrative regulation involving several participants in starch synthesis, including starch synthases (SSs), starch branching/debranching enzymes (SBEs/DBEs). Therefore, I further detected the expression of related genes on transcription level and the enzymatic activity of their respective proteins. Results indicated altered gene expression of several regulators in these mutants, particularly demonstrating dramatic alterations in dpe2 and dpe2ss4 with leaf aging. These changes corresponded with the observed alterations in starch granule morphology.
Taken together, I have identified and characterized a progressive alteration in starch granule morphology primarily resulting from the deficiencies in DPE2 and MEX1. Furthermore, I have associated the CLD pattern with the granule morphogenesis, as well as the gene expression and enzymatic activity of proteins involved in starch synthesis. Unlike SS4, which is implicated in starch initiation, MEX1 and DPE2 are involved into starch degradation. MEX1 is located in chloroplast envelope and DPE2 is situated in the cytosol. Considering the locations and known functions of DPE2/MEX1 and SS4, I infer that there might be two pathways influencing starch morphology: an initiation-affected pathway via SS4 and a degradation-affected pathway via DPE2/MEX1.
Climate change, driven by increasing atmospheric levels of carbon dioxide (CO2), presents a significant societal challenge for the 21st century. Biotechnological approaches for microbial production of commodity chemicals and fuels offer possible solutions to re-fix CO2 from the atmosphere, thereby mitigating carbon emissions and contributing to a sustainable carbon-economy in the future. Biological CO2 fixation is also at the heart of agricultural productivity, where photosynthesis and the Calvin-Benson-Bassham cycle present promising biotechnological targets for crop improvement.
Synthetic biology allows testing metabolic solutions not known to exist in nature, which may exceed their natural counterparts in terms of efficiency. In this thesis, I explore the design of such new-to-nature metabolic pathways for biological CO2 utilization and their implementation in living cells (in vivo).
In the first chapter, I describe the development of a metabolic pathway that enables intracellular conversion of CO2 to formate, giving access to highly efficient carbon fixation routes. In nature, CO2-reduction remains restricted to anaerobic organisms and low redox potentials. Here, we introduce the “CORE cycle”, a synthetic metabolic pathway that converts CO2 to formate under fully aerobic conditions and ambient CO2 levels, using only NADPH as a reductant. We leverage this synthetic, ATP-energized pathway to overcome the thermodynamic and kinetic barriers associated with CO2-reduction. Applying rational metabolic engineering and adaptive evolution, this work demonstrates that Escherichia coli can utilize ambient CO2 as the sole source of one-carbon units and serine, achieving a first step towards novel modes of synthetic autotrophy. We further apply computational modeling to showcase the potential of the CORE cycle as a photorespiratory bypass for enhancing photosynthesis.
In the second chapter, I describe the development of the “LCM module”, a novel metabolic route for CO2-incorporating conversion of acetyl-CoA to pyruvate. This route relies on the newly uncovered, promiscuous activity of an adenosylcobalamin (B12)-dependent enzyme, which we significantly optimize through targeted hypermutation and in vivo selection strategies. The LCM module provides a shorter and more efficient pathway for acetyl-CoA assimilation compared to natural routes, offering novel opportunities for synthetic CO2 fixation.
Overall, through theoretical pathway analysis, enzyme bioprospecting, and modular metabolic engineering in E. coli, this thesis expands the solution space for biological CO2 fixation.
The African weakly electric fish genus Campylomormyrus includes 15 described species mostly native to the Congo River and its tributaries. They are considered sympatric species, because their distribution area overlaps. These species generate species-specific electric organ discharges (EODs) varying in waveform characteristics, including duration, polarity, and phase number. They exhibit also pronounced divergence in their snout, i.e. the length, thickness, and curvature. The diversifications in these two phenotypical traits (EOD and snout) have been proposed as key factors promoting adaptive radiation in Campylomormyrus. The role of EODs as a pre-zygotic isolation mechanism driving sympatric speciation by promoting assortative mating has been examined using behavioral, genetical, and histological approaches. However, the evolutionary effects of the snout morphology and its link to species divergence have not been closely examined. Hence, the main objective of this study is to investigate the effect of snout morphology diversification and its correlated EOD to better understand their sympatric speciation and evolutionary drivers. Moreover, I aim to utilize the intragenus and intergenus hybrids of Campylomormyrus to better understand trait divergence as well as underlying molecular/genetic mechanisms involved in the radiation scenario. To this end, I utilized three different approaches: feeding behavior analysis, diet assessment, and geometric morphometrics analysis. I performed feeding behavior experiments to evaluate the concept of the phenotype-environment correlation by testing whether Campylomormyrus species show substrate preferences. The behavioral experiments showed that the short snout species exhibits preference to sandy substrate, the long snout species prefers a stone substrate, and the species with intermediate snout size does not exhibit any substrate preference. The experiments suggest that the diverse feeding apparatus in the genus Campylomormyrus may have evolved in adaptation to their microhabitats. I also performed diet assessments of sympatric Campylomormyrus species and a sister genus species (Gnathonemus petersii) with markedly different snout morphologies and EOD using NGS-based DNA metabarcoding of their stomach contents. The diet of each species was documented showing that aquatic insects such as dipterans, coleopterans and trichopterans represent the major diet component. The results showed also that all species are able to exploit diverse food niches in their habitats. However, comparing the diet overlap indices showed that different snout morphologies and the associated divergence in the EOD translated into different prey spectra. These results further support the idea that the EOD could be a ‘magic trait’ triggering both adaptation and reproductive isolation. Geometric morphometrics method was also used to compare the phenotypical shape traits of the F1 intragenus (Campylomormyrus) and intergenus (Campylomormyrus species and Gnathonemus petersii) hybrids relative to their parents. The hybrids of these species were well separated based on the morphological traits, however the hybrid phenotypic traits were closer to the short-snouted species. In addition, the likelihood that the short snout expressed in the hybrids increases with increasing the genetic distance of the parental species. The results confirmed that additive effects produce intermediate phenotypes in F1-hybrids. It seems, therefore, that morphological shape traits in hybrids, unlike the physiological traits, were not expressed straightforward.
Mitochondria and plastids are organelles with an endosymbiotic origin. During evolution, many genes are lost from the organellar genomes and get integrated in the nuclear genome, in what is known as intracellular/endosymbiotic gene transfer (IGT/EGT). IGT has been reproduced experimentally in Nicotiana tabacum at a gene transfer rate (GTR) of 1 event in 5 million cells, but, despite its centrality to eukaryotic evolution, there are no genetic factors known to influence the frequency of IGT in higher eukaryotes. The focus of this work was to determine the role of different DNA repair pathways of double strand break repair (DSBR) in the integration step of organellar DNA in the nuclear genome during IGT. Here, a CRISPR/Cas9 mutagenesis strategy was implemented in N. tabacum, with the aim of generating mutants in nuclear genes without expected visible phenotypes. This strategy led to the generation of a collection of independent mutants in the LIG4 (necessary for non-homologous end joining, NHEJ) and POLQ genes (necessary for microhomology mediated end joining, MMEJ). Targeting of other DSBR genes (KU70, KU80, RPA1C) generated mutants with unexpectedly strong developmental phenotypes.. These factors have telomeric roles, hinting towards a possible relationship between telomere length, and strength of developmental disruption upon loss of telomere structure in plants. The mutants were made in a genetic background encoding a plastid-encoded IGT reporter, that confers kanamycin resistance upon transfer to the nucleus. Through large scale independent experiments, increased IGT from the chloroplast to the nucleus was observed in lig4 mutants, as well as lines encoding a POLQ gene with a defective polymerase domain (polqΔPol). This shows that NHEJ or MMEJ have a double-sided relationship with IGT: while transferred genes may integrate using either pathway, the presence of both pathways suppresses IGT in wild-type somatic cells, thus demonstrating for the first time the extent on which nuclear genes control IGT frequency in plants. The IGT frequency increases in the mutants are likely mediated by increased availability of double strand breaks for integration. Additionally, kinetic analysis reveals that gene transfer (GT) events accumulate linearly as a function of time spent under antibiotic selection in the experiment, demonstrating that, contrary to what was previously thought, there is no such thing as a single GTR in somatic IGT experiments. Furthermore, IGT in tissue culture experiments appears to be the result of a "race against the clock" for integration in the nuclear genome, that starts when the organellar DNA arrives to the nucleus granting transient antibiotic resistance. GT events and escapes of kanamycin selection may be two possible outcomes from this race: those instances where the organellar DNA gets to integrate are recovered as GT events, and in those cases where timely integration fails, antibiotic resistance cannot be sustained, and end up considered as escapes. In the mutants, increased opportunities for integration in the nuclear genome change the overall ratio between IGT and escape events. The resources generated here are promising starting points for future research: (1) the mutant collection, for the further study of processes that depend on DNA repair in plants (2) the collection of GT lines obtained from these experiments, for the study of the effect of DSBR pathways over integration patterns and stability of transferred genes and (3) the developed CRISPR/Cas9 workflow for mutant generation, to make N. tabacum meet its potential as an attractive model for answering complex biological questions.
The G protein-coupled estrogen receptor (GPER1) is acknowledged as an important mediator of estrogen signaling. Given the ubiquitous expression of GPER1, it is likely that the receptor plays a role in a variety of malignancies, not only in the classic hormonally regulated tissues (e.g., breast, ovary, and prostate), but also in the colon. As colorectal cancer (CRC) is the third most common cancer in both men and women worldwide and environmental factors and dietary habits are important risk factors, it is increasingly recognized that natural and synthetic hormones and their associated receptors might play a role in CRC. Through oral consumption, environmental contaminants with endocrine activity are in contact with the gastrointestinal mucosa, where they might exert their toxic effects. Although GPER1 has been shown to be engaged in physiological and pathophysiological processes, its role in CRC remains poorly understood. Thus, pro- as well as anti-tumorigenic effects are described in the literature. This thesis has uncovered novel roles of GPER1 in mediating major CRC-associated phenotypes in transformed and non-transformed colon cell lines. Exposure to the estrogens 17β-estradiol (E2), bisphenol-A (BPA) and diethylstilbestrol (DES) but also the androgen dihydrotestosterone (DHT) resulted in GPER1-dependent induction of supernumerary centrosomes, whole chromosomal instability (w-CIN) and aneuploidy. Indeed, both knockdown and inhibition of GPER1 attenuated the generation of (xeno)hormone-driven supernumerary centrosomes and karyotype instability. Mechanistically, (xeno)hormone-induced centrosome amplification was associated with transient multipolar mitosis and the generation of so called anaphase “lagging” chromosomes. The results of this thesis propose a GPER1/PKA/AKAP9-pathway in regulating centrosome numbers in colorectal cancer cells and the involvement of the centriolar protein centrin. Remarkably, exposure to (xeno)hormones resulted in atypical enlargement and unexpected phosphorylation of the centriole marker centrin in interphase. These findings provide a novel role for GPER1 in key CRC-prone lesions and shed light on underlying mechanisms that involve GPER1 function in the colon. Elucidating to what extent centrosomal proteins are involved in the GPER1-mediated aneugenic effect will be an important task for future studies. The present study was intended to lay a first foundation to understand the molecular basis and potential risk factors of CRC which might help to reduce the use of laboratory animals. Since numerous animal experiments are conducted in biomedical research, the development of alternative methods is indispensable. The Federal Institute for Risk Assessment (BfR) as the German Center for the Protection of Laboratory Animals (Bf3R) addresses this issue by uncovering underlying mechanisms leading to colorectal cancer as necessary prerequisite in order to develop alternative methods.
Photosynthesis converts light into metabolic energy which fuels plant growth. In nature, many factors influence light availability for photosynthesis on different time scales, from shading by leaves within seconds up to seasonal changes over months. Variability of light energy supply for photosynthesis can limit a plant´s biomass accumulation. Plants have evolved multiple strategies to cope with strongly fluctuation light (FL). These range from long-term optimization of leaf morphology and physiology and levels of pigments and proteins in a process called light acclimation, to rapid changes in protein activity within seconds. Therefore, uncovering how plants deal with FL on different time scales may provide key ideas for improving crop yield. Photosynthesis is not an isolated process but tightly integrates with metabolism through mutual regulatory interactions. We thus require mechanistic understanding of how long-term light acclimation shapes both, dynamic photosynthesis and its interactions with downstream metabolism. To approach this, we analyzed the influence of growth light on i) the function of known rapid photosynthesis regulators KEA3 and VCCN1 in dynamic photosynthesis (Chapter 2-3) and ii) the interconnection of photosynthesis with photorespiration (PR; Chapter 4).
We approached topic (i) by quantifying the effect of different growth light regimes on photosynthesis and photoprotection by using kea3 and vccn1 mutants. Firstly, we found that, besides photosynthetic capacity, the activities of VCCN1 and KEA3 during a sudden high light phase also correlated with growth light intensity. This finding suggests regulation of both proteins by the capacity of downstream metabolism. Secondly, we showed that KEA3 accelerated photoprotective non-photochemical quenching (NPQ) kinetics in two ways: Directly via downregulating the lumen proton concentration and thereby de-activating pH-dependent NPQ, and indirectly via suppressing accumulation of the photoprotective pigment zeaxanthin.
For topic (ii), we analyzed the role of PR, a process which recycles a toxic byproduct of the carbon fixation reactions, in metabolic flexibility in a dynamically changing light environment. For this we employed the mutants hpr1 and ggt1 with a partial block in PR. We characterized the function of PR during light acclimation by tracking molecular and physiological changes of the two mutants. Our data, in contrast to previous reports, disprove a generally stronger physiological relevance of PR under dynamic light conditions. Additionally, the two different mutants showed pronounced and distinct metabolic changes during acclimation to a condition inducing higher photosynthetic activity. This underlines that PR cannot be regarded purely as a cyclic detoxification pathway for 2PG. Instead, PR is highly interconnected with plant metabolism, with GGT1 and HPR1 representing distinct metabolic modulators.
In summary, the presented work provides further insight into how energetic and metabolic flexibility is ensured by short-term regulators and PR during long-term light acclimation.
The light reactions of photosynthesis are carried out by a series of multiprotein complexes embedded in thylakoid membranes. Among them, photosystem I (PSI), acting as plastocyanin-ferderoxin oxidoreductase, catalyzes the final reaction. Together with light-harvesting antenna I, PSI forms a high-molecular-weight supercomplex of ~600 kDa, consisting of eighteen subunits and nearly two hundred co-factors. Assembly of the various components into a functional thylakoid membrane complex requires precise coordination, which is provided by the assembly machinery. Although this includes a small number of proteins (PSI assembly factors) that have been shown to play a role in the formation of PSI, the process as a whole, as well as the intricacy of its members, remains largely unexplored.
In the present work, two approaches were used to find candidate PSI assembly factors. First, EnsembleNet was used to select proteins thought to be functionally related to known PSI assembly factors in Arabidopsis thaliana (approach I), and second, co-immunoprecipitation (Co-IP) of tagged PSI assembly factors in Nicotiana tabacum was performed (approach II).
Here, the novel PSI assembly factors designated CO-EXPRESSED WITH PSI ASSEMBLY 1 (CEPA1) and Ycf4-INTERACTING PROTEIN 1 (Y4IP1) were identified. A. thaliana null mutants for CEPA1 and Y4IP1 showed a growth phenotype and pale leaves compared with the wild type. Biophysical experiments using pulse amplitude modulation (PAM) revealed insufficient electron transport on the PSII acceptor side. Biochemical analyses revealed that both CEPA1 and Y4IP1 are specifically involved in PSI accumulation in A. thaliana at the post-translational level but are not essential. Consistent with their roles as factors in the assembly of a thylakoid membrane protein complex, the two proteins localize to thylakoid membranes. Remarkably, cepa1 y4ip1 double mutants exhibited lethal phenotypes in early developmental stages under photoautotrophic growth. Finally, co-IP and native gel experiments supported a possible role for CEPA1 and Y4IP1 in mediating PSI assembly in conjunction with other PSI assembly factors (e.g., PPD1- and PSA3-CEPA1 and Ycf4-Y4IP1). The fact that CEPA1 and Y4IP1 are found exclusively in green algae and higher plants suggests eukaryote-specific functions. Although the specific mechanisms need further investigation, CEPA1 and Y4IP1 are two novel assembly factors that contribute to PSI formation.
The musculoskeletal system provides support and enables movement to the body, and its deterioration is a crucial aspect of age-related functional decline. Mesenchymal stromal cells (MSCs) play an important role in musculoskeletal homeostasis due to their broad differentiation potentials and their ability to support osteogenic and myogenic tissue maintenance and regeneration. In the bone, MSCs differentiate either into osteochondrogenic progenitors to form osteocytes and chondrocytes, or increasingly with age into adipogenic progenitors which give rise to bone-resident adipocytes. In skeletal muscle, during healthy regeneration MSCs provide regulatory signals that activate local, tissue-specific stem cells, known as satellite cells, which regenerate contractile myofibres. This process involves a significant cross-talk to immune cells stemming from both lymphoid and myeloid lineages. During ageing, muscle-resident MSCs undergo increased adipogenic lineage commitment, causing niche changes that contribute to fatty infiltration in muscles. These shifts in cell populations in bone lead to the loss of osteogenic cells and subsequently osteoporosis, or in muscle to impaired regeneration and to the development of sarcopenia. However, the signals that drive transition of MSCs into their respective cellular fates remain elusive.
This thesis aims to elucidate the transcriptional shifts modulating cell states and cell types in musculoskeletal MSC fate determination. Single-cell RNA-sequencing (scRNA-seq) was used to characterise cell type-specific transcript regulation. State-of-the-art bioinformatics tools were combined with different analytical platforms that include both droplet-based scRNA-seq for large heterogeneous populations, and microfluidics-based scRNA-seq to assess small, rare subpopulations. For each platform, distinct computational pipelines were established including filtering steps to exclude low-quality cells, and data visualisation was performed by dimensionality reduction. Downstream analysis included clustering, cell type annotation, and differential gene expression to investigate transcriptional states in defined cell types during ageing and injury in the muscle and bone. Finally, a novel tool to assess publication activities in defined areas of research for the identified marker genes was developed.
The results in the bone indicate that ageing MSCs increasingly commit towards an adipogenic fate at the expense of osteogenic specialisation. The data also suggests that significant cell population shifts of MSC-type fibro-adipogenic progenitors during muscle ageing underlie the pathologies observed in homeostatic and post-injury regenerative conditions. High-throughput visualisation of publication activity for candidate genes enabled more effective biological evaluation of scRNA-seq data. These results expose critical age-related changes in the stem cell niches of skeletal muscle and bone, highlight their respective sensitivity to nutrition and pathology, and elucidate novel factors that modulate stem cell-based regeneration. Targeting these processes might improve musculoskeletal health in the context of ageing and prevent the negative effects of pathological lineage determination.
Pichia pastoris (syn. Komagataella phaffi) is a distinguished expression system widely used in industrial production processes. Recent molecular research has focused on numerous approaches to increase recombinant protein yield in P. pastoris. For example, the design of expression vectors and synthetic genetic elements, gene copy number optimization, or co-expression of helper proteins
(transcription factors, chaperones, etc.). However, high clonal variability of transformants and low screening throughput have hampered significant success.
To enhance screening capacities, display-based methodologies inherit the potential for efficient isolation of producer clones via fluorescence-activated cell sorting (FACS). Therefore, this study focused on developing a novel clone selection method that is based on the non-covalent attachment of Fab fragments on the P. pastoris cell surface to be applicable for FACS.
Initially, a P. pastoris display system was developed, which is a prerequisite for the surface capture of secreted Fabs. A Design of Experiments approach was applied to analyze the influence of various genetic elements on antibody fragment display. The combined P. pastoris formaldehyde dehydrogenase promoter (PFLD1), Saccharomyces cerevisiae invertase 2 signal peptide (ScSUC2), - agglutinin (ScSAG1) anchor protein, and the ARS of Kluyveromyces lactis (panARS) conferred highest display levels.
Subsequently, eight single-chain variable fragments (scFv) specific for the constant part of the Fab heavy or light chain were individually displayed in P. pastoris. Among the tested scFvs, the anti-human CH1 IgG domain scFv allowed the most efficient Fab capture detected by flow cytometry.
Irrespective of the Fab sequence, exogenously added as well as simultaneously secreted Fabs were successfully captured on the cell surface. Furthermore, Fab secretion capacities were shown to correlate to the level of surface-bound Fabs as demonstrated for characterized producer clones.
Flow-sorted clones presenting high amounts of Fabs showed an increase in median Fab titers (factor of 21 to 49) compared to unsorted clones when screened in deep-well plates. For selected candidates, improved functional Fab yields of sorted cells vs. unsorted cells were confirmed in an upscaled shake flask production. Since the scFv capture matrix was encoded on an episomal plasmid with inherently unstable autonomously replicating sequences (ARS), efficient plasmid curing was observed after removing the selective pressure. Hence, sorted clones could be immediately used for production without the need to modify the expression host or vector. The resulting switchable display/secretion system provides a streamlined approach for the isolation of Fab producers and subsequent Fab production.
Unveiling the Local Universe
(2023)
Potato FLC-like and SVP-like proteins jointly control growth and distinct developmental processes
(2023)
Based on worldwide consumption, Solanum tuberosum L. (potato) is the most important non-grain food crop. Potato has two ways of stable propagation: sexually via flowering and vegetatively via tuberization. Remarkably, these two developmental processes are controlled by similar molecular regulators and mechanisms. Given that FLC and SVP genes act as key flowering regulators in the model species Arabidopsis and in various other crop species, this study aimed at identifying FLC and SVP homologs in potato and investigating their roles in the regulation of plant development, with a particular focus on flowering and tuberization. Our analysis demonstrated that there are five FLC-like and three SVP like proteins encoded in the potato genome. The expression profiles of StFLCs and StSVPs throughout potato development and the detected interactions between their proteins indicate tissue specificity of the individual genes and distinct roles of a variety of putative protein complexes. In particular, we discovered that StFLC-D, as well as StFLC-B, StSVP-A, and StSVP-B play a complex role in the regulation of flowering time, as not only increased but also decreased levels of their transcripts promote earlier flowering. Most importantly, StFLC-D has a marked impact on tuberization under non-inductive conditions and susceptibility to temperature-induced tuber malformation, also known as second growth. Plants with decreased levels of StFLC-D demonstrated a strong ability to produce tubers under long days and appeared to be insensitive to temperature-induced second growth. Lastly, our data also suggests that StFLCs and StSVPs may be involved in the nitrogen-dependent regulation of potato development. Taken together, this study highlights the functional importance of StFLC and StSVP genes in the regulation of distinct developmental processes in potato.
Social networking sites
(2023)
Arthur Schopenhauer (1788–1860) was perhaps the last polymath among the great Germanic philosophers. Switching with ease and elegance between epistemic positions and fields as diverse as idealism and empiricism, fideism and rationalism, realism and nominalism, art and religion, jurisprudence and politics, psychology and occultism, Schopenhauer erected an imposing edifice bearing testimony to his universal learning. This study is an investigation into the very conclusion of Schopenhauer’s philosophy and endeavours to answer the following question: did Schopenhauer’s doctrine of salvation issue forth organically from his intellectual output or was it annexed to his philosophy as a result of his critical engagement with religion? The labyrinthine paths through which Schopenhauer arrives at the soteriological culmination of his philosophy are subjected to critical assessment; the picture that emerges is of a philosopher who seemed convinced that he had solved some of the most pressing cosmic riddles to have tormented mankind through the ages.
Functional characterization of ROS-responsive genes, ANAC085 and ATR7, in Arabidopsis thaliana
(2023)
Biostimulant SuperFifty based molecular priming to increase plant strength and stress tolerance
(2023)
In times of ongoing biodiversity loss, understanding how communities are structured and what mechanisms and local adaptations underlie the patterns we observe in nature is crucial for predicting how future ecological and anthropogenic changes might affect local and regional biodiversity. Aquatic zooplankton are a group of primary consumers that represent a critical link in the food chain, providing nutrients for the entire food web. Thus, understanding the adaptability and structure of zooplankton communities is essential. In this work, the genetic basis for the different temperature adaptations of two seasonally shifted (i.e., temperature-dependent) occurring freshwater rotifers of a formerly cryptic species complex (Brachionus calyciflorus) was investigated to understand the overall genetic diversity and evolutionary scenario for putative adaptations to different temperature regimes. Furthermore, this work aimed to clarify to what extent the different temperature adaptations may represent a niche partitioning process thus enabling co-existence. The findings were then embedded in a metacommunity context to understand how zooplankton communities assemble in a kettle hole metacommunity located in the northeastern German "Uckermark" and which underlying processes contribute to the biodiversity patterns we observe. Using a combined approach of newly generated mitochondrial resources (genomes/cds) and the analysis of a candidate gene (Heat Shock Protein 40kDa) for temperature adaptation, I showed that the global representatives of B. calyciflorus s.s.. are genetically more similar than B. fernandoi (average pairwise nucleotide diversity: 0.079 intraspecific vs. 0.257 interspecific) indicating that both species carry different standing genetic variation. In addition to differential expression in the thermotolerant B. calyciflorus s.s. and thermosensitive B. fernandoi, the HSP 40kDa also showed structural variation with eleven fixed and six positively selected sites, some of which are located in functional areas of the protein. The estimated divergence time of ~ 25-29 Myr combined with the fixed sites and a prevalence of ancestral amino acids in B. calyciflorus s.s. indicate that B. calyciflorus s.s. remained in the ancestral niche, while B. fernandoi partitioned into a new niche. The comparison of mitochondrial and nuclear markers (HPS 40kDa, ITS1, COI) revealed a hybridisation event between the two species. However, as hybridisation between the two species is rare, it can be concluded that the temporally isolated niches (i.e., seasonal-shifted occurrence) they inhabit based on their different temperature preferences most likely represent a pre-zygotic isolation mechanism that allows sympatric occurrence while maintaining species boundaries. To determine the processes underlying zooplankton community assembly, a zooplankton metacommunity comprising 24 kettle holes was sampled over a two-year period. Active (i.e., water samples) and dormant communities (i.e., dormant eggs hatched from sediment) were identified using a two-fragment DNA metabarcoding approach (COI and 18S). Species richness and diversity as well as community composition were analysed considering spatial, temporal and environmental parameters. The analysis revealed that environmental filtering based on parameters such as pH, size and location of the habitat patch (i.e., kettle hole) and surrounding field crops largely determined zooplankton community composition (explained variance: Bray-Curtis dissimilarities: 10.5%; Jaccard dissimilarities: 12.9%), indicating that adaptation to a particular habitat is a key feature of zooplankton species in this system. While the spatial configuration of the kettle holes played a minor role (explained variance: Bray-Curtis dissimilarities: 2.8% and Jaccard dissimilarities: 5.5%), the individual kettle hole sites had a significant influence on the community composition. This suggests monopolisation/priority effects (i.e., dormant communities) of certain species in individual kettle holes. As environmental filtering is the dominating process structuring zooplankton communities, this system could be significantly influenced by future land-use change, pollution and climate change.
Heat stress (HS) is one of the major abiotic stresses which adversely affects the survival and growth of plants due to their sessile nature. To combat the detrimental effects of HS and develop thermotolerance, plants have evolved several defense mechanisms. Thermomemory is one such molecular mechanism whereby plants that have been acclimated (or primed/P) by a moderate HS can respond more efficiently and continue their growth after exposure to a severe or lethal HS (called triggering/T), while unprimed plants cannot survive. Thermomemory is known to be regulated by several transcription factors (TFs), epigenetic changes, chromatin remodellers, post-transcriptional changes and it also involves protein stability control and primary metabolism adjustment. Recent research has suggested that the shoot apical meristem (SAM) in Arabidopsis thaliana has a distinct transcriptional thermomemory which is possibly regulated by eight TFs called HEAT SHOCK FACTORS (HSFs). The main objective of this PhD thesis is to investigate the role of HSFA7b (one of the eight HSFs), in regulating thermomemory at the SAM by identifying the molecular networks it regulates. HSFA7a, a close homolog of HSFA7b, is also one of the eight HSFs that are involved in regulating thermomemory at the SAM. Thermomemory was found to be defective in the hsfa7b and hsfa7a hsfa7b mutants; the percentage survival of these seedlings was significantly lower than in wild-type (WT) seedlings after the priming and triggering (PT) treatment. Transcriptome and ChIP analyses were performed to identify the molecular networks controlled by HSFA7b and its close homolog HSFA7a, in regulating thermomemory at the SAM. The chromatin regulator SPLAYED (SYD) was found to be regulated by both HSFA7a and HSFA7b at the SAM during thermomemory. SYD is directly involved in SAM maintenance by directly regulating WUSCHEL (WUS), a master regulator of stem cell maintenance. WUS expression was down-regulated at the SAM of PT treated hsfa7a/b mutants compared to WT-Col-0 seedlings. HSFA7a and HSFA7b also jointly regulate the expression of orphan gene QUA QUINE STARCH (QQS) during thermomemory. Starch accumulation negatively correlates with QQS expression and this trend was observed in WT plants in response to thermopriming. The remobilization of starch was affected in the hsfa7a/b mutants compared to WT plants during the recovery period after T treatment. These findings indicate that defects in SAM maintenance and starch remobilization could possibly contribute to the reduced thermomemory in the hsfa7a/b mutants. Moreover, transcriptome and ChIP analysis indicate that ethylene signaling genes are directly regulated by HSFA7b during thermomemory. Transcriptome analysis of the HSFA7b-IOE line indicates that HSFA7b positively regulates the expression of HEAT STRESS ASSOCIATED 32 (HSA32), an important thermomemory gene, and HSFA7b strongly suppresses the expression of the reactive oxygen species (ROS) responsive REDOX RESPONSIVE TRANSCRIPTION FACTOR 1 (RRTF1) gene, which is also a repressed target of SYD. In Arabidopsis, the HSFA7b transcript undergoes alternative splicing at high temperatures to form two splice variants: one correctly/constitutively spliced variant which is functional and codes for the HSFA7b protein and one intron retained splice variant. Higher accumulation of the functional HSFA7b splice variant was found at the SAM compared to other tissues. Moreover, accumulation of the functional splice variant was higher in P and PT plants compared to control plants, whereas higher levels of the intron retained splice variant is found in plants subjected directly to the T treatment. The intron retained HSFA7b splice variant is degraded by the non-sense mediated decay (NMD) pathway as a means of regulating transcript level essential for protein synthesis at high temperatures. Importantly, HSFA7b protein accumulation was observed in plants subjected to PT treatment that survive and continue growth, but not in plants subjected directly to T treatment that do not survive, indicating that constitutive/ correct splicing of the HSFA7b transcript is a component of thermomemory. Taken together, these findings suggest that HSFA7a and HSFA7b jointly regulate SAM maintenance via the chromatin remodeller SYD and starch remobilization via QQS. In addition to them, HSFA7b also regulates the expression of ethylene signaling genes, heat responsive genes and the ROS responsive RRTF1. Furthermore, constitutive/correct splicing in the HSFA7b transcript is also an essential component of thermomemory.
Functional materials, also called "Smart Materials", are described by their ability to fulfill a desired task through targeted interaction with its environment. Due to this functional integration, such materials are of increased interest, especially in areas where the increasing micronization of components is required. Modern manufacturing processes (e.g. microfluidics) and the availability of a wide variety of functional materials (e.g. shape memory materials) now enable the production of particle-based switching components. This category includes micropumps and microvalves, whose basic function is the active control of liquid flows. One approach in realizing those microcomponents as pursued by this work, enables variable size-switching of water-filled microballoons by implementing a stimulus-sensitive switching motif in the capsule's membrane shell, while being under the influence of a constant driving force. The switching motif with its gatekeeper function has a critical influence on one or more material parameters, which modulate the capsule's resistance against the driving force in microballoon expansion process. The advantage of this concept is that even non-variable analyte conditions, such as concentration levels of ions, can be capitalized to generate external force fields that, under the control of the membrane, cause an inflation of the microballoon by an osmotically driven water influx. In case of osmotic pressure gradients as the driving force for the capsule expansion, material parameters associated with the gatekeeper function are specifically the permeability and the mechanical stiffness of the shell material. While a modulation of the shell permeability could be utilized to kinetically impede the water influx on large time scales, a modulation of the shell's mechanical stiffness even might be utilized to completely prevent the capsule inflation due to a possible non-deformability beneath a certain threshold pressure. In polymer networks, which are a suitable material class for the demanded capsule shell because of their excellent elasticity, both the permeability and the mechanical properties are strongly influenced by the crystallinity of the material. Since the permeability is effectively reduced with increasing crystallinity, while the mechanical stiffness is simultaneously greatly increased, both effects point in the same direction in terms of their functional relationship. For this reason and due to a reversible and contactless modulation of the membrane crystallinity by heat input, crystallites may be suitable switching motifs for controlling the capsule expansion. As second design element of reversible expandable microballoons, the capsule geometry, defined by an aqueous core enveloped by the temperature-sensitive polymer network membrane, should allow an osmotic pressure gradient across the membrane layer. The strength of the inflation pressure and the associated inflation velocity upon membrane melting should be controlled by the salt concentration within the aqueous core, while a turn in the osmotic gradient should furthermore allow the reversible process of capsule deflation. Therefore, it should be possible to build either microvalves and micropumps, while their intended action of either pumping or valving is determined by their state of expansion and the direction of the osmotic pressure gradient.. Microballoons of approximately 300 µm in diameter were formed via droplet-based microfluidics from double-emulsion templates (w/o/w). The elastomeric capsule membrane was formed by photo-crosslinking of methacrylate (MA) functionalized oligo(ε-caprolactone) precursors (≈ 3.8 MA-arms, Mn ≈ 12000 g mol-1) within the organic medium layer (o) via UV-exposure after droplet-formation. After removal of the toluene/chloroform mixture by slow extraction via the continuous aqueous phase, the capsules solidified under the development of a characteristic "mushroom"-like shape at specific experimental conditions (e.g. λ = 308 nm, 57 mJ·s-1·cm-2, 16 min). It could be furthermore shown that in dependency to the process parameters: oligomer concentration and curing-time also spherical capsules were accessible. Long curing-times and high oligomer concentrations at a fixed light-intensity favored the formation of "mushroom"-like capsules, whereas the contrary led to spherical shaped capsules. A comparative study on thin polymer network films of same composition and equal treatment proved a correlation between the film's crosslink density and their contraction capability, while stronger crosslinked polymer networks showed a stronger contraction after solvent removal. In combination with observations during capsule solidification via light-microscopy, where a continuous shaping from almost spherical crosslinked templates to "mushroom"-shaped and solidified capsules was stated, the following mechanism was proposed. In case of low oligomer contents and short curing-times, the contraction of the capsule shell during solvent removal is strongly diminished due to a low degree of crosslinking. Therefore, the solidifying shell could freely collapse onto the aqueous core. In the other case, high oligomer concentrations and long curing-times will favor the formation of highly crosslinked capsule membranes with a strong contraction capability. Due to an observed decentered location of the aqueous core within the swollen polymer network, an uneven radial stress along the capsule's circumference is exerted to the incompressible core. This lead to an uneven contraction during solvent removal and a directed flow of the core fluid into the direction of the minimal stress vector. In consequence, the initially thicker spherical cap contracts, whereas the opposing thinner spherical cap get stretched. The "mushroom"-shape over some advantages over their spherical shaped counterparts, why they were selected for the further experiments. Besides the necessity of a high density of crosslinking for the purpose of extraordinary elasticity and toughness, the form-anisotropy promotes a faster microballoon expandability due to a partial reduction of the membrane thickness. Additionally, pre-stretched regions of thin thickness might provide a better resistance against inflation pressure than spherical but non-stretched capsules of equal membrane thickness. The resulting "mushroom"-shaped microcapsules exhibited a melting point of Tm ≈ 50 - 60 °C and a degree of crystallinity of Xc ≈ 29 - 38 % depending on the membrane thickness and internal salt content, which is slightly lower than for the non-crosslinked oligomer and reasoned by a limited chain mobility upon crosslinking. Nonetheless, the melting transition of the polymer network was associated with a strong drop in its mechanical stiffness, which was shown to have a strong influence on the osmotic driven expansion of the microcapsules. Capsules that were subjected to osmotic pressures between 1.5 and 4.7 MPa did not expand if the temperature was well below the melting point of the capsule's membrane, i.e. at room temperature. In contrast, a continuous expansion, while approaching asymptotically to a final capsule size, was observed if the temperature exceeded the melting point, i.e. 60 °C. Microballoons, which were kept for 56 days at ∆Π = 1.5 MPa and room temperature, did not change significantly in diameter, why the impact of the mechanical stiffness on the expansion behavior is considered to be the greater than the influence of the shell permeability. The time-resolved expansion behavior of the microballoons above their Tm was subsequently modeled, using difusion equations that were corrected for shape anisotropy and elastic restoring forces. A shape-related and expansion dependent pre-factor was used to dynamically address the influence of the shell thickness differences along the circumference on the inflation velocity, whereas the microballoon's elastic contraction upon inflation was rendered by the inclusion of a hyperelastic constitutive model. An important finding resulting from this model was the pronounced increase in inflation velocity compared to hypothetical capsules with a homogeneous shell thickness, which stresses the benefit of employing shape anisotropic balloon-like capsules in this study. Furthermore, the model was able to predict the finite expandability on basis of entropy-elastic recovery forces and strain-hardening effects. A comparison of six different microballoons with different shell thicknesses and internal salt contents showed the linear relationship between the volumetric expansion, the shell thickness and the applied osmotic pressure, as represented by the model. As the proposed model facilitates the prediction of the expansion kinetics depending on the membranes mechanical and diffusional characteristics, it might be a screening tool for future material selections. In course of the microballoon expansion process, capsules of intermediate diameters could be isolated by recrystallization of the membrane, which is mainly caused by a restoration of the membrane's mechanical stiffness and is otherwise difficult to achieve with other stimuli-sensitive systems. The capsule's crystallinity of intermediate expansion states was nearly unchanged, whereas the lamellar crystal size tends to decreased with the expansion ratio. Therefore, it was assumed that the elastic modulus was only minimally altered and might increased due to the networks segment-chain extension. In addition to the volume increase achieved by inflation, a turn in the osmotic gradient also facilitated the reversible deflation, which was shown in inflation/deflation cycles. These both characteristics of the introduced microballoons are important parameter regarding the realization of micropumps and microvalves. The fixation of expanded microcapsules via recrystallization enabled the storage of entropy-elastic strain-energy, which could be utilized for pumping actions in non-aqueous media. Here, the pumping velocity depended on both, the type of surrounding medium and the applied temperature. Surrounding media that supported the fast transport of pumped liquid showed an accelerated deflation, while high temperatures further accelerate the pumping velocity. Very fast rejection of the incorporated payload was furthermore realized with pierced expanded microballoons, which were subjected to temperatures above their Tm. The possible fixation of intermediate particle sizes provide opportunities for vent constructions that allowed the precise adjustment of specific flow-rates and multiple valve openings and closings. A valve construction was realized by the insertion of a single or multiple microballoons in a microfluidic channel. A complete and a partial closing of the microballoon-valves was demonstrated as a function of the heating period. In this context, a difference between the inflation and deflation velocity was stated, summarizing slower expansion kinetics. Overall, microballoons, which presented both on-demand pumping and reversible valving by a temperature-triggered change in the capsule's volume, might be suitable components that help to design fully integrated LOC devices, due to the implementation of the control switch and controllable inflation/deflation kinetics. In comparison to other state of the art stimuli-sensitive materials, one has to highlight the microballoons capability of stabilizing almost continuously intermediate capsule sizes by simple recrystallization of the microballoon's membrane.
The increasing global population has led to a growing demand for cost-effective and eco-friendly methods of water purification. This demand has reached a peak due to the increasing presence of impurities and pollutants in water and a growing awareness of waterborne diseases. Advanced oxidation processes (AOPs) are effective methods to address these challenges, due to the generation of highly reactive radicals, such as sulfate radical (SO4•-), hydroxyl radical (•OH), and/or superoxide radical (•O2-) in oxidation reactions. Relative to conventional hydrogen peroxide (H2O2)-based AOPs for wastewater treatment, the persulfate-related AOPs are receiving increasing attention over the past decades, due to their stronger oxidizing capability and a wider pH working window. Further deployment of the seemingly plausible technology as an alternative for the well-established one in industry, however, necessitates a careful evaluation of compounding factors, such as water matrix effects, toxicological consequences, costs, and engineering challenges, etc. To this end, rational design of efficient and environmentally friendly catalysts constitutes an indispensable pathway to advance persulfate activation efficacy and to elucidate the mechanisms in AOPs, the combined endeavors are expected to provide insightful understanding and guidelines for future studies in wastewater treatment. A dozens of transition metal-based catalysts have been developed for persulfate-related AOPs, while the undesirable metal leaching and poor stability in acidic conditions have been identified as major obstacles. Comparatively, the carbonaceous materials are emerging as alternative candidates, which are characterized by metal-free nature, wide availability, and exceptional resistance to acid and alkali, as well as tunable physicochemical and electronic properties, the combined merits make them an attractive option to overcome the aforementioned limitations in metal-based catalytic systems. This dissertation aims at developing novel carbonaceous materials to boost the activity in peroxymonosulfate (PMS) activation processes. Functionalized carbon materials with metal particles or heteroatoms were constructed and further evaluated in terms of their ability to activate PMS for AOPs. The main contents of this thesis are summarized as follows: (1) Iron oxide-loaded biochar: improving stability and alleviating metal leakage Metal leaching constitutes one of the main drawbacks in using transition metals as PMS activators, which is accompanied by the generation of metal-containing sludge, potentially leading to secondary pollution. Meanwhile, the metal nanoparticles are prone to aggregate, causing rapid decay of catalytic performance. The use of carbons as supports for transition metals could mitigate these deficiencies, because the interaction between metals and carbons could in turn disperse and stabilize metal nanoparticles, thus suppressing the metal leaching. In this work, the environmentally benign lignin with its abundant phenolic groups, which is well known to serve as carbon source with high yields and flexibility, was utilized to load Fe ions. The facile low-temperature pre-treatment pyrolytic strategy was employed to construct a green catalyst with iron oxides embedded in Kraft-lignin-derived biochar (termed as γ-Fe2O3@KC). The γ-Fe2O3@KC was capable of activating PMS to generate stable non-radical species (1O2 and Fe (V)=O) and to enhance electron transfer efficiency. A surface-bound reactive complex (catalyst-PMS*) was identified by electrochemical characterizations and discussed with primary surface-bound radical pairs to explain the contradictions between quenching and EPR detection results. The system also showed encouraging reusability for at least 5 times and high stability at pH 3-9. The low concentration of iron in γ-Fe2O3@KC/PMS system implied that the carbon scaffold of biochar substantially alleviated metal leakage. (2) MOF-derived nanocarbon: new carbon crystals Traditional carbon materials are of rather moderate performance in activation PMS, due to the poor electron transfer capacity within the amorphous structure and limited active sites for PMS adsorption. Herein, we established crystalline nanocarbon materials via a simple NaCl-templated strategy using the monoclinic zeolitic imidazolate framework-8 (ZIF-8) sealed with NaCl crystals as the precursors. Specifically, NaCl captured dual advantages in serving as structure-directing agent during hydrolysis and protective salt reactor to facilitate phase transformation during carbonization. The structure-directing agent NaCl provided a protective and confined space for the evolution of MOF upon carbonization, which led to high doping amounts of nitrogen (N) and oxygen elements (O) in carbon framework (N: 14.16 wt%, O: 9.6 wt%) after calcination at a high temperature of 950 oC. We found that N-O co-doping can activate the chemically inert carbon network and the nearby sp2-hybridized carbon atoms served as active sites for adsorption and activation. Besides, the highly crystallized structure with well-established carbon channels around activated carbon atoms could significantly accelerate electron transfer process after initial adsorption of PMS. As such, this crystalline nanocarbon exhibited excellent catalytic kinetics for various pollutants. (3) MOF-derived 2D carbon layers: enhanced mass/electron transfer The two-dimensional (2D) configuration of carbon-based nanosheets with inherent nanochannels and abundant active sites residing on the layer edges or in between the layers, allowed the accessible interaction and close contact between the substrates and reactants, as well as the dramatically improved electron- and mass-transfer kinetics. In this regard, we developed dual-templating strategy to afford 2D assembly of the crystalline carbons, which found efficiency in reinforcing the interactions between the catalyst surface and foreign pollutants. Specifically, we found that the ice crystals and NaCl promoted the evolution of MOF in a 2D fashion during the freezing casting stage, while the later further allowed the formation of a graphitic surface at high calcination temperature, by virtue of the templating effect of molten salt. Due to the highly retained co-doping amounts, N and O heteroatoms created abundant active sites for PMS activation, the 2D configuration of carbon-based nanosheets enable efficient interaction of PMS and pollutants on the surface, which further boosted the kinetics of degradation.