@phdthesis{vonBismarck2023,
  author    = {von Bismarck, Thekla},
  title     = {The influence of long-term light acclimation on photosynthesis in dynamic light},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 163},
  year      = {2023},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Uflewski2021,
  author    = {Uflewski, Michal},
  title     = {Characterizing the regulation of proton antiport across the thylakoid membrane},
  school      = {Universit{\"a}t Potsdam},
  pages     = {122},
  year      = {2021},
  abstract  = {Die Energie, die zum Antrieb photochemischer Reaktionen ben{\"o}tigt wird, stammt aus der Ladungstrennung an der Thylakoidmembran. Aufrgrund des Unterschieds in der Protonenkonzentration zwischen dem Stroma der Chloroplasten und dem Thylakoidlumen wird eine Protonenmotorische Kraft (pmf) erzeugt. Die pmf setzt sich aus dem Protonengradienten (ΔpH) und dem Membranpotential (ΔΨ) zusammen, die gemeinsam die ATP-Synthese antreiben. In der Natur schwankt die Energiemenge, die die Photosynthese antreibt, aufgrund h{\"a}ufiger {\"A}nderungen der Lichtintensit{\"a}t. Der Thylakoid-Ionentransport kann den Energiefluss durch einen Photosyntheseapparat an die Lichtverf{\"u}gbarkeit anpassen, indem er die pmf-Zusammensetzung ver{\"a}ndert. Die Dissipation von ΔΨ verringert die Ladungsrekombination am Photosystem II, so dass ein Anstieg der ΔpH-Komponente eine R{\"u}ckkopplung zur Herabregulierung der Photosynthese ausl{\"o}sen kann. Der durch den K+-Austausch-Antiporter 3 (KEA3) gesteuerte K+/H+-Antiport reduziert den ΔpH-Anteil von pmf und d{\"a}mpft dadurch das nicht-photochemische Quenching (NPQ). Infolgedessen erh{\"o}ht sich die Photosyntheseeffizienz beim {\"U}bergang zu geringerer Lichtintensit{\"a}t. Ziel dieser Arbeit war es, Antworten auf Fragen zur Regulierung der KEA3-Aktivit{\"a}t und ihrer Rolle in der Pflanzenentwicklung zu finden. Die vorgestellten Daten zeigen, dass KEA3 in Pflanzen, denen der Chloroplasten-ATP-Synthase-Assembly-Faktor CGL160 fehlt und die eine verminderte ATP-Synthase-Aktivit{\"a}t aufweisen, eine zentrale Rolle bei der Regulierung der Photosynthese und des Pflanzenwachstums unter station{\"a}ren Bedingungen spielt. Das Fehlen von KEA3 in der cgl160-Mutante f{\"u}hrt zu einer starken Beeintr{\"a}chtigung des Wachstums, da die Photosynthese aufgrund des erh{\"o}hten pH-abh{\"a}ngigen NPQs und des verringerten Elektronenflusses durch den Cytochrom b6f-Komplex eingeschr{\"a}nkt ist. Die {\"U}berexpression von KEA3 in der cgl160-Mutante erh{\"o}ht die Ladungsrekombination im Photosystem II und f{\"o}rdert die Photosynthese. In Zeiten geringer ATP-Synthase-Aktivit{\"a}t profitieren die Pflanzen also von der KEA3-Aktivit{\"a}t. KEA3 unterliegt einer Dimerisierung {\"u}ber seinen regulatorischen C-Terminus (RCT). Der RCT reagiert auf Ver{\"a}nderungen der Lichtintensit{\"a}t, da die Pflanzen, die KEA3 ohne diese Dom{\"a}ne exprimieren, einen reduzierten Lichtschutzmechanismus bei Lichtintensit{\"a}tsschwankungen aufweisen. Allerdings fixieren diese Pflanzen w{\"a}hrend der Photosynthese-Induktionsphase mehr Kohlenstoff als Gegenleistung f{\"u}r einen langfristigen Photoprotektor, was die regulierende Rolle von KEA3 in der Pflanzenentwicklung zeigt. Der KEA3-RCT ist dem Thylakoidstroma zugewandt, so dass seine Regulierung von lichtinduzierten Ver{\"a}nderungen in der Stroma-Umgebung abh{\"a}ngt. Die Regulierung der KEA3-Aktivit{\"a}t {\"u}berschneidet sich mit den pH-{\"A}nderungen im Stroma, die bei Lichtschwankungen auftreten. Es hat sich gezeigt, dass ATP und ADP eine Affinit{\"a}t zum heterolog exprimierten KEA3 RCT haben. Eine solche Wechselwirkung verursacht Konformations{\"a}nderungen in der RCT-Struktur. Die Faltung der RCT-Liganden-Interaktion h{\"a}ngt vom pH-Wert der Umgebung ab. Mit einer Kombination aus Bioinformatik und In-vitro-Ansatz wurde die ATP-Bindungsstelle am RCT lokalisiert. Das Einf{\"u}gen einer Punktmutation in der KEA3-RCT Bindungsstelle in planta f{\"u}hrte zu einer Deregulierung der Antiporteraktivit{\"a}t beim {\"U}bergang zu wenig Licht. Die in dieser Arbeit vorgestellten Daten erm{\"o}glichten es uns, die Rolle von KEA3 bei der Anpassung der Photosynthese umfassender zu bewerten und Modelle zur Regulierung der KEA3-Aktivit{\"a}t w{\"a}hrend des {\"U}bergangs zwischen verschiedenen Lichtintensit{\"a}ten vorzuschlagen.},
  language  = {en}
}
@phdthesis{Rolo2023,
  author    = {Rolo, David},
  title     = {Assembly of photosystem I in thylakoid membranes},
  school      = {Universit{\"a}t Potsdam},
  pages     = {177},
  year      = {2023},
  abstract  = {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.},
  language  = {en}
}