Archiv der bisher stattgefundenen Seminare

Gastgeber: Ute Armbruster

CANCELED - Emilie Wientjes - How do plants optimize photosynthetic light-harvesting under various light conditions?

May 2020
[mehr]

Anja Schneider - Manganese Transporter in Chloroplasts

[mehr]

Danja Schünemann - Protein transport to the thylakoid membrane of chloroplasts – Insights into evolution and mechanisms

October 2019
[mehr]

Toshiharu Shikanai - Chloroplast NDH-PSI supercomplex; structure, assembly and physiological function

[mehr]

Elias Kaiser - Photosynthesis in fluctuating light: physiological control and environmental modulation

June 2018
[mehr]

Cornelia Spetea Wiklund - Thylakoid K+ and Cl- Channels and Transporters Regulate Photosynthesis in a Rapidly Changing Environment

June 2017
Abstract In variable light environments, plants rapidly adjust photosynthesis for an optimal balance between photochemistry and photoprotection. There is increasing evidence that ion fluxes across thylakoid membranes play an important role in regulation of photosynthesis. Recent work from our laboratory have unraveled the roles of the K+/H+ antiporter KEA3, the putative Cl− channel CLCe and the voltage-dependent Cl− channel VCCN1 in thylakoid ion homeostasis and photosynthetic regulation in Arabidopsis thaliana. However, the current knowledge about these transport proteins comes from the characterization of single loss-of-function mutants of the corresponding genes in Arabidopsis, which do not provide information about possible functional relationships between K+ and Cl− fluxes in the thylakoid membrane. In my seminar, I will provide an overview of the current knowledge about genes involved in ion fluxes and regulation of photosynthesis and present data from characterization of higher-order mutants of KEA3, CLCe and VCCN1. Our findings contribute to understanding the thylakoid network of ion fluxes and how they help plants to adjust photosynthesis in variable light environments. [mehr]

Shizue Matsubara - Long-term acclimation of Arabidopsis to highly fluctuating light environment

Natural light environment is highly variable in both intensity and spectral quality. The light intensity can vary between zero (night) and >2000 μmol photons m-2 s-1 (full sunlight) as the earth rotates, weather changes and wind moves branches and leaves. Upon sudden and large increase in light intensity, photosynthesis is limited biochemically, e.g. by the activation state of RubisCO and the availability of the Calvin-Benson cycle intermediates or inorganic phosphate for ATP synthesis. Low stomatal conductance may also limit plant’s capacity to utilize additional light energy for photosynthesis. When put under highly fluctuating light conditions for days, Arabidopsis plants primarily or initially downregulate photosynthetic light harvesting and linear electron transport while upregulating photoprotection at the expense of carbon gain and growth. Towards understanding the mechanisms of long-term acclimation to highly fluctuating light environment, we studied leaf transcriptome, metabolome and proteome of Arabidopsis (Columbia wild type). Plants were exposed to highly fluctuating light or constant light condition for 3 or 7 days to focus on long-lasting (non-transient) acclimatory changes and downstream responses that may give rise to the phenotypic alterations. Given the pronounced diurnal and circadian variations in leaf metabolism and gene expression, samples were taken at two contrasting time points during the light period in the 12 h/12 h light/dark cycle, namely, early morning and at the end of the day. Furthermore, young and mature leaves were analyzed separately as they typically differ in the photosynthetic capacity. Overall, our results underscore photo-oxidative stress responses and mitigation of acceptor-side limitation to photosynthesis during acclimation to highly fluctuating light. The gene expression profiles revealed distinct responses of young and mature leaves in the morning and at the end of the day, indicating crosstalk between long-term acclimation, leaf development and circadian clock. In particular, I will highlight the changes related to the components of photosynthesis and photoprotection. [mehr]

Hans-Henning Kunz - Using the chloroplast envelope carrier mutant kea1kea2 to probe the impact of abiotic stress on photosynthesis and the plant ion homeostasis

Drought and soil salinity represent two tightly linked abiotic stress factors. Together they by far cause the most damaging effects on annual crop yields. Although evidence for the importance of the chloroplast in surviving these adverse environmental effects have existed for years still the molecular processes are not well understood. Recently, several independent laboratories have started to investigate the plastid ion transport mechanisms. Particularly K+ flux was found to be crucial in maintaining the chloroplast ion and pH homeostasis and to fine-tune photosynthesis. This carefully balanced system can be readily disturbed by abiotic stress. For instance, during salt stress toxic Na ions also accumulate in chloroplasts, where they replace K+ ions and diminish photosynthetic efficiency in plants. This could supposedly be prevented by controlling the ion flux across the envelope membrane via ion carries and channels. The kea1kea2 mutant that lacks two highly active K+/H+ antiporters is strongly growth compromised with poor photosynthesis under normal growth conditions. However, if exposed to soil salinity mutants flourish with highly recovered photosynthetic efficiency. My lab is interested in deciphering the molecular foundation of this phenomenon. By doing so, we anticipate to find the missing ion transport mechanisms in the envelope membrane. In my seminar I will show some early data on how we approach this endeavor and what we plan to do in the next few years. [mehr]

Dagmar Lyska - Beyond green – harvesting and dissipating light energy in the heterokont alga Nannochloropsis oceanica

Understanding the fundamental processes of photosynthesis and its regulation has become more and more important with growing energy and agricultural demands and the need to enhance feedstock performance and yields. Until recently, research on photosynthesis has been focused largely on cyanobacteria, green algae and land plants. However, heterokont microalgae, such as Nannochloropsis, are emerging as potential feedstocks for biofuels due to their high photoautotrophic biomass and lipid accumulation rates. The photosynthetic properties of Nannochloropsis are similar to, but also significantly different, from green algae, e.g. in terms of light harvesting or dissipation of excess light energy (Non-Photochemical Quenching, NPQ). We want to understand these mechanisms and their regulation in Nannochloropsis and therefore designed molecular tools for the genetic modification of this non-model organism. Using a non-lethal, easy-to-screen mutant phenotype, we have established protocols for targeted gene knockout by homologous recombination and by the CRISPR/Cas9 system for the Nannochloropsis oceanica strain CCMP1779. Furthermore, we have created a library of random insertional mutants with altered NPQ capacities and/ or kinetics and identified disrupted genes using PCR-based methods. Combining the forward and reverse genetics approaches with biochemical and spectroscopic analyses, we are now able to address the significance of the xanthophyll cycle-dependent vs. the LHCX(LHCSR)-dependent component of NPQ and the molecular basis of light harvesting in Nannochloropsis. [mehr]

Thilo Rühle - Assembly of chloroplast F1F0–ATP synthases

March 2016
F1F0-ATP synthases are multiprotein complexes, which are found in all living organisms. They meet the cellular demand for ATP and maintain ion gradients across membranes by an ion-flux-dependent, reversible ATP synthesis/hydrolysis reaction. Bacterial, mitochondrial and chloroplast F1F0-ATP synthases share the same core structure: a soluble F1 domain responsible for reversible ATP generation is connected by two stalks to the ion-translocating membrane domain. Correct assembly of F1F0-ATP synthases depends on multiple, intertwined cellular processes, and is even more challenging in eukaryotic organelles, since here – in addition to tight regulation of subunit transcription and translation – coordination of organellar import processes and two protein synthesis machineries is essential. Thus, biogenesis of F1Fo-ATP synthases requires the intervention of auxiliary factors, which carry out specialized functions in this highly concerted process. In a search for novel photosynthesis-relevant factors in Arabidopsis thaliana, proteins were considered that are shared by photosynthetic eukaryotes from the green lineage but that are not found in non-photosynthetic eukaryotes. Those proteins are called GreenCut proteins and are likely to be associated with chloroplast functions. Knockout mutant lines were isolated and analyzed with respect to photosynthetic perturbations using a chlorophyll fluorescence screening procedure. As a result, we could identify two GreenCut proteins, which are specifically required for chloroplast F1F0-ATP synthase accumulation and provided evidence that they are involved in chloroplast F1F0-ATP synthase assembly. [mehr]

Flow cytometry as a method to sort microalgae and bacteria based on intracellular energy reserves

Many microorganisms accumulate high-energy compounds such as triacylglycerols (TAG) and polyphosphate (polyP) in intracellular granules. These compounds provide energy reserves for the cell to survive suboptimal conditions. Additionally, recent findings have suggested that these high-energy granules are not simply for energy storage, but have important cellular roles involved in protein folding, gene expression and signaling, among others. In addition to understanding the functional significance of these energy reserves, identifying mutants or strains with increased accumulation of TAG or polyP is of biotechnological interest due to our current dependence on non-renewable energy and phosphate sources (i.e. fossil fuel and phosphate mining). In this talk, I will present the use of flow cytometry as a high-throughput screen to detect and enrich for cells hyper-accumulating TAG or polyP. I will first talk about the method we have developed for isolating mutants with increased lipid accumulation in model alga Chlamydomonas reinhardtii. In this approach, 50% of the isolated mutants have a reproducible high lipid phenotype. Secondly, I will present ongoing work on wastewater bacterial community screening for polyP hyper-accumulating strains. Initial findings suggest that bacterial species stemming from phylum Firmicutes and alphaproteobacteria may have a larger role in phosphate removal from wastewater than previously expected. [mehr]

Quenching of excess light energy: PsbS, one big part of the puzzle

Sunlight is the ultimate energy source driving photosynthesis. In nature, however, absorbed light energy often exceeds the capacity of light utilization in photosynthesis, giving rise to the formation of reactive oxygen species and thus photo-oxidative damage of the chloroplast. Non-photochemical quenching of excitation energy (NPQ) in the antenna of Photosystem II (PSII) allows the harmless dissipation of excess light energy as heat and thereby avoids oxidative damage to the photosynthetic apparatus. Four different mechanisms contribute to NPQ, termed qT, qE, qZ and qI. Under saturating light conditions, the energy dependent-quenching mechanism (qE) represents the dominant NPQ component; qE is based on a complex mechanism which strictly depends on three factors: (i) lumen pH, (ii) the PsbS protein and (iii) the xanthophyll zeaxanthin (Zx). According to the current understanding of qE, a low pH in the thylakoid lumen induces PsbS-dependent conformational changes in the PSII antenna and formation of Zx, both being central for activation of maximum qE capacity. The central role of PsbS in these processes is related to the function of PsbS as sensor of lumenal pH. Our work focuses on the identification of protein interaction partners of PsbS and how these interactions contribute to the pH-regulated reorganization of the PSII antenna during activation of NPQ. Additionally, we are interested in the role of PsbS in green algae as an approach to understand the evolution of photoprotective mechanisms. Altogether, our findings support that throughout land colonization of plants, PsbS evolved as a key player in energy dissipation by modulating light induced protein interactions in the PSII-Antenna required for the activation of qE. [mehr]
Web-Ansicht
Seite Drucken
Im neuen Fenster öffnen
Geschätzte DIN-A4 Seiten-Breite
Zur Redakteursansicht