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Auxin transport in algae
Skokan, Roman ; Petrášek, Jan (advisor) ; Bíšová, Kateřina (referee)
Phytohormone auxin plays an important role in regulating plant development. Directional (polar) cell-to-cell auxin transport creates auxin gradients within plant tissues, which trigger a specific developmental response. The vast majority of available data concerns angiosperms. Lower land plants have been much less explored in this regard, but the important auxin-related mechanisms (including polar auxin transport) are already present in mosses. To uncover the origins of auxin action, one must focus on green algae, especially of clade Streptophyta, which are the direct ancestors of all land plants. In this study, the possible effects of auxins, both native and synthetic, were investigated on two algae: basal, unicellular Chlorella lobophora and advanced, filamentous Spirogyra sp. The latter received comparably more attention, since it belongs to a clade now acknowledged as a sister group to land plants. Chlorella lobophora culture growth was irresponsive to synthetic auxin NAA. The average Spirogyra sp. cell length was, however, changed by auxins at high concentrations. By conducting accumulation assays of radioactively labelled auxins and HPLC analysis, auxin metabolism and transport was investigated in Spirogyra sp. This alga was able to metabolize the plant-native IAA, but not synthetic auxins...
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New insights on auxin metabolism
Helusová, Lenka ; Müller, Karel (advisor) ; Ryšlavá, Helena (referee)
Auxin is the longest known phytohormone with many functions. It participates in the development of embryo, in vegetative and generative development, plant stress reaction, and also in their senescence and death. Activity of auxin in plant cells and tissues is quite often compared to the effect of morphogens, i.e. the effect of substances, whose concentrations induce a strictly defined response in tissue and organ formation. Apart from intercellular and intracellular auxin transport, the main determinants of auxin concentration gradients are its biosynthesis and metabolism. Regardless of the long-lasting study of auxin, the complexity of metabolic pathway regulation is still not well known. The aim of this thesis is to summarize current knowledge of the metabolism of auxin in plants, i.e. its biosynthetic pathways, conjugation and oxidation, and put them into a context with older results.
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The evolution of auxin homeostasis mechanisms
Skokan, Roman ; Petrášek, Jan (advisor) ; Buschmann, Henrik (referee) ; Holzinger, Andreas (referee)
The evolution of auxin homeostasis mechanisms Ph.D. thesis Roman Skokan, 2021 Abstract The streptophyte lineage consists of land plants (embryophytes) and several groups of primarily freshwater green algae called charophytes. While the phytohormone auxin is a conserved regulator of land plant development, little has been known of the possible origins of auxin response mechanisms in charophytes. We found that one of these mechanisms, the cellular auxin efflux via the PIN family of transport proteins, is most likely a deeply conserved feature in streptophytes. Additionally, we investigated the state of conservation in the green lineage (Viridiplantae) of the gene families known to be involved in auxin transport in land plants. We revealed that some families are deeply conserved outside land plants, but not others. We also helped uncover a unique radiation within the PIN family in Charophyceae. Striving to uncover the native significance of auxin transport in charophytes, we discovered a growth response to exogenously-applied auxin in Closterium, though the effort to produce stable mutant lines in the native PIN homolog is still underway. Altogether, we brought important insights into the evolution of auxin transport and response in the streptophyte lineage, though many questions still remain.
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New insights on auxin metabolism
Helusová, Lenka ; Müller, Karel (advisor) ; Ryšlavá, Helena (referee)
Auxin is the longest known phytohormone with many functions. It participates in the development of embryo, in vegetative and generative development, plant stress reaction, and also in their senescence and death. Activity of auxin in plant cells and tissues is quite often compared to the effect of morphogens, i.e. the effect of substances, whose concentrations induce a strictly defined response in tissue and organ formation. Apart from intercellular and intracellular auxin transport, the main determinants of auxin concentration gradients are its biosynthesis and metabolism. Regardless of the long-lasting study of auxin, the complexity of metabolic pathway regulation is still not well known. The aim of this thesis is to summarize current knowledge of the metabolism of auxin in plants, i.e. its biosynthetic pathways, conjugation and oxidation, and put them into a context with older results.
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Mechanism of auxin transport across plasma membrane through PIN auxin efflux carriers
Lefnar, Radek ; Petrášek, Jan (advisor) ; Nodzynski, Tomasz (referee)
Phytohormone auxin and its directional distribution plays an essential role in the regulation of numerous processes during vegetative and reproductive plant development. Regulation of the expression, localization and activity of the PIN-FORMED (PIN) proteins is important for proper polar auxin transport in plant tissues. PIN proteins have been described as the major auxin efflux carriers regulating auxin's directional flow to build up gradients that provide information for the coordination of plant development. PIN protein structure topology prediction through bioinformatic analysis is still insufficient to understand their transport mechanism. Experimental analysis of PIN protein domains can provide valuable insight into understanding their role in mediating auxin transport. In this study, the C-terminal part of PINs have been modified by gradual trimming to determine the existence of relevant functional domains, which could be important for auxin transport. Seven modified PIN proteins from Arabidopsis thaliana and Nicotiana tabacum were prepared. Transiently transformed tobacco cell line Bright Yellow-2 (BY-2) was used to monitor differences in PIN transport activity. This approach allowed indirect monitoring of intracellular auxin levels using the DR5 reporter system. Transiently expressed...
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Auxin transport in algae
Skokan, Roman ; Petrášek, Jan (advisor) ; Bíšová, Kateřina (referee)
Phytohormone auxin plays an important role in regulating plant development. Directional (polar) cell-to-cell auxin transport creates auxin gradients within plant tissues, which trigger a specific developmental response. The vast majority of available data concerns angiosperms. Lower land plants have been much less explored in this regard, but the important auxin-related mechanisms (including polar auxin transport) are already present in mosses. To uncover the origins of auxin action, one must focus on green algae, especially of clade Streptophyta, which are the direct ancestors of all land plants. In this study, the possible effects of auxins, both native and synthetic, were investigated on two algae: basal, unicellular Chlorella lobophora and advanced, filamentous Spirogyra sp. The latter received comparably more attention, since it belongs to a clade now acknowledged as a sister group to land plants. Chlorella lobophora culture growth was irresponsive to synthetic auxin NAA. The average Spirogyra sp. cell length was, however, changed by auxins at high concentrations. By conducting accumulation assays of radioactively labelled auxins and HPLC analysis, auxin metabolism and transport was investigated in Spirogyra sp. This alga was able to metabolize the plant-native IAA, but not synthetic auxins...
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Evoluce mechanismů transportu auxinu.
Skokan, Roman ; Petrášek, Jan (advisor) ; Cvrčková, Fatima (referee)
Auxin, the longest studied phytohormone, is distinguished from other phytohormones by its unique directional, so-called polar transport. This feature helps to facilitate the broad range of auxin action at all stages of plant development. The polar auxin transport has been evolving together with plant lineages. By studying the mechanisms of auxin transport, biosynthesis, metabolism and particularly signaling we can perhaps better elucidate many milestones of plant evolution, such as complex multicellularity or transition to land. This bachelor thesis summarizes the available data and gives a basic overview of auxin-related characteristics. As far as we know, the advanced mechanisms of auxin transport and signaling known from land plants are probably not very ancient and are absent in various algae. Auxin biosynthesis, however, is rather common and a lot of green algae contain orthologs of important biosynthetic enzymes from land plants. Based on the available data it seems that a complete auxin signalling pathway coupled with proteasomal degradation and affecting gene expression is not present in algae. The polar auxin transport, so far with the earliest evidence from moss sporophytes, was recently found in the gametophytic thallus of stonewort (Chara) from a green algal clade Streptophyta, which is...
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Auxin Transport in Arabidopsis thaliana: From the whole plant to suspension cultured cells
Seifertová, Daniela ; Zažímalová, Eva (advisor) ; Opatrný, Zdeněk (referee) ; Hejátko, Jan (referee)
in English Plants with their sessile life-style are exposed to many stimuli from environment. They have developed mechanisms how to coordinate their growth and development, which allows them to survive sometimes in very difficult conditions. Plant hormones are one of the most important regulators of this signal transduction. Auxins, as the oldest known group of plant hormones, play important role in many physiological processes in plants. To allow perceiving the information in every single cell, auxin molecule is transported by cell-to-cell manner. Auxin molecules enter the cell by passive diffusion or by active uptake by auxin influx carriers. To reach the next cell, they are transported actively out of the cell by auxin efflux carriers. Athough active auxin transport has been studied for almost four decades, past two decades contributed to the identification and characterization of particular auxin carriers remarkably. This thesis contributes to the knowledge on the auxin efflux and influx carriers and their involvement in the processes occurring from a single cell level to the level of a whole plant. Firstly, it brings detailed description of auxin transport characteristics in Arabidopsis thaliana cell suspension cells (Ath cells). Secondly, it shows that the overproduction of PIN1 auxin efflux...
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The role of actin dynamics in auxin transport
Stillerová, Lenka ; Cvrčková, Fatima (advisor) ; Schwarzerová, Kateřina (referee)
Phytohormones are signalling molecules directing physiological and developmental processes in plants. One of them, auxin, is involved in the diverse regulation of plant processes, e.g. embryogenesis, organogenesis, vascular tissue formation and tropisms. Auxin transport is polar. Auxin isdistributed via the phloem, utilizing specialized membrane transport proteins; small amount diffuse also through the membrane. Aux1/Lax transporters mediate auxin entry into the cell, auxin efflux is mediate mostly by PIN transporters, which are the crucial factors in determining the directionality of auxin flow. Asymmetric localization of membrane PIN proteins depends on vesicle transport from Golgi to the plasma membrane. Vesicles are transported along actin filaments which are dynamically rebuilted by regulators. They are maintaining asymmetric cellular localization of the auxin transport proteins. PIN proteins are cycling between endosomes and plasma membrane. Cycling is regulated by ARF-GEF proteins and serin/threonin kinase (PID, PINOID). Newly synthesized PIN proteins are equally distributed in the plasma membrane, afterwards they are asymmetrically redistributed. Regulation of actin filaments formation and remodelling is the crucial factor for transport of vesicles with PIN proteins. Many proteins which regulate...
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