Stefan Timm | University of Rostock (original) (raw)

Papers by Stefan Timm

Plant Cell and Environment, Jun 2, 2023

Plants contain three NADPH‐thioredoxin reductases (NTR) located in the cytosol/mitochondria (NTRA... more Plants contain three NADPH‐thioredoxin reductases (NTR) located in the cytosol/mitochondria (NTRA/B) and the plastid (NTRC) with important metabolic functions. However, mutants deficient in all NTRs remained to be investigated. Here, we generated and characterised the triple Arabidopsis ntrabc mutant alongside with ntrc single and ntrab double mutants under different environmental conditions. Both ntrc and ntrabc mutants showed reduced growth and substantial metabolic alterations, especially in sink leaves and under high CO2 (HC), as compared to the wild type. However, ntrabc showed higher effective quantum yield of PSII under both constant and fluctuating light conditions, altered redox states of NADH/NAD+ and glutathione (GSH/GSSG) and lower potential quantum yield of PSII in sink leaves in ambient but not high CO2 concentrations, as compared to ntrc, suggesting a functional interaction between chloroplastic and extra‐chloroplastic NTRs in photosynthesis regulation depending on leaf development and environmental conditions. Our results unveil a previously unknown role of the NTR system in regulating sink leaf metabolism and plant acclimation to HC, while it is not affecting full plant development, indicating that the lack of the NTR system can be compensated, at least to some extent, by other redox mechanisms.

bioRxiv (Cold Spring Harbor Laboratory), Apr 3, 2022

Redox regulation of mitochondrial dihydrolipoamide dehydrogenase (mtLPD1) simultaneously modulate... more Redox regulation of mitochondrial dihydrolipoamide dehydrogenase (mtLPD1) simultaneously modulates photorespiration, the tricarboxylic acid (TCA)-cycle and branched chain amino acid (BCAA) degradation in response to rapid environmental changes.

When the supply of inorganic carbon is limiting, photosynthetic cyanobacteria excrete nitrite, a ... more When the supply of inorganic carbon is limiting, photosynthetic cyanobacteria excrete nitrite, a toxic intermediate in the ammonia assimilation pathway from nitrate. While it has been hypothesized that the excreted nitrite represents excess nitrogen that could not be further assimilated due to the missing carbon, the underlying molecular mechanism has remained enigmatic. Here, we characterized a hitherto unannotated gene with homologs in the genomes of 485 different cyanobacteria that is upregulated under low carbon conditions and controlled by the transcription factor NtcA, a central regulator of nitrogen homeostasis. To understand its function, we ectopically overexpressed it in Synechocystis sp. PCC 6803, which resulted in a chlorotic phenotype, delayed growth, severe changes in amino acid pools, and nitrite excretion. Coimmunoprecipitation experiments revealed that this protein targets nitrite reductase, a central enzyme in the assimilation of ammonia from nitrate/nitrite, and w...

Methods in molecular biology, 2017

Transfer DNA (T-DNA) insertional lines have facilitated reverse genetic approaches in plant scien... more Transfer DNA (T-DNA) insertional lines have facilitated reverse genetic approaches in plant science and considerably accelerated the functional characterization of genes. Typically, online databases of mutant collections are searched for suitable mutant alleles of the gene of interest (GOI). Before such lines can be characterized physiologically, the genotype of the respective mutant has to be verified followed by the quantitative examination of downstream effects on the levels of the respective mRNA and the encoded protein. Here, we describe a typical workflow for the identification of photorespiratory mutants followed by phenotypic characterization according to growth under different conditions, photosynthesis on the levels of chlorophyll a fluorescence and gas exchange, and metabolite analysis.

Journal of Experimental Botany, Dec 8, 2021

Science of The Total Environment

Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences freque... more Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences frequent changes in salinity. They are often exposed to mechanical disturbances (like wave, currents, storms) forcing them to bury deeper into the sediment to get a better foothold. In nature, these stressors often occurs simultaneously. Osmotic stress negatively affects the burial activity and the physiological performances of soft shell clam, Mya arenaria; however, the mechanism behind this is still unknown. In this dataset we present the effect of different salinity regime on the burial activity of Mya arenaria, as well as the combined effect of osmotic stress and repeated burrowing on the succinate dehydrogenase and ATPase activity in foot muscle of Mya arenaria.

Plants, 2022

Fluctuating light (FL) is a typical natural light stress that can cause photodamage to photosyste... more Fluctuating light (FL) is a typical natural light stress that can cause photodamage to photosystem I (PSI). However, the effect of growth light on FL-induced PSI photoinhibition remains controversial. Plants grown under high light enhance photorespiration to sustain photosynthesis, but the contribution of photorespiration to PSI photoprotection under FL is largely unknown. In this study, we examined the photosynthetic performance under FL in tomato (Lycopersicon esculentum) plants grown under high light (HL-plants) and moderate light (ML-plants). After an abrupt increase in illumination, the over-reduction of PSI was lowered in HL-plants, resulting in a lower FL-induced PSI photoinhibition. HL-plants displayed higher capacities for CO2 fixation and photorespiration than ML-plants. Within the first 60 s after transition from low to high light, PSII electron transport was much higher in HL-plants, but the gross CO2 assimilation rate showed no significant difference between them. There...

Glycine decarboxylase controls photosynthesis and plant growth

Die Photorespiration ist essentiell für das Leben von Pflanzen in der heutigen Atmosphäre. Der Au... more Die Photorespiration ist essentiell für das Leben von Pflanzen in der heutigen Atmosphäre. Der Ausfall von Schlüsselenzymen dieses Stoffwechselwegs führt zu strenger Sauerstoffsensitivität der entsprechenden Mutanten. Diese Studie repräsentiert die einzige Ausnahme von der bisher allgemeingültigen Regel. Die Mutation der peroxisomalen Hydroxypyruvat-Reduktase (HPR1) zieht nur geringe Beeinträchtigungen des Wachstums nach sich. Eingehende Analysen der AtHPR1-Mutanten führten zur Identifikation der alternativen HPR2 und zeigten erstmals die Beteiligung des Zytosols an der Photorespiration.

Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences freque... more Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences frequent changes in salinity. They are often exposed to mechanical disturbances (like wave, currents, storms) forcing them to bury deeper into the sediment to get a better foothold. In nature, these stressors often occurs simultaneously. Osmotic stress negatively affects the burial activity and the physiological performances of soft shell clam, Mya arenaria; however, the mechanism behind this is still unknown. In this dataset we present the combined effect of osmotic stress and repeated burrowing on the concentration on different amino acids and short chain organic acids in the whole body tissue of Mya arenaria.

Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences freque... more Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences frequent changes in salinity. They are often exposed to mechanical disturbances (like wave, currents, storms) forcing them to bury deeper into the sediment to get a better foothold. In nature, these stressors often occurs simultaneously. Osmotic stress negatively affects the burial activity and the physiological performances of soft shell clam, Mya arenaria; however, the mechanism behind this is still unknown. In this dataset we present the combined effect of osmotic stress and repeated burrowing on the trypsin- and chymotrypsin-like proteasomal and lysosomal activity in gill tissue and digestive gland of Mya arenaria.

eLife, 2022

The decarboxylation of pyruvate is a central reaction in the carbon metabolism of all organisms. ... more The decarboxylation of pyruvate is a central reaction in the carbon metabolism of all organisms. It is catalyzed by the pyruvate:ferredoxin oxidoreductase (PFOR) and the pyruvate dehydrogenase (PDH) complex. Whereas PFOR reduces ferredoxin, the PDH complex utilizes NAD+. Anaerobes rely on PFOR, which was replaced during evolution by the PDH complex found in aerobes. Cyanobacteria possess both enzyme systems. Our data challenge the view that PFOR is exclusively utilized for fermentation. Instead, we show, that the cyanobacterial PFOR is stable in the presence of oxygen in vitro and is required for optimal photomixotrophic growth under aerobic and highly reducing conditions while the PDH complex is inactivated. We found that cells rely on a general shift from utilizing NAD(H)-dependent to ferredoxin-dependent enzymes under these conditions. The utilization of ferredoxins instead of NAD(H) saves a greater share of the Gibbs free energy, instead of wasting it as heat. This obviously sim...

Bioturbators such as sediment-dwelling marine bivalves are ecosystem engineers that enhance sedim... more Bioturbators such as sediment-dwelling marine bivalves are ecosystem engineers that enhance sediment-water exchange and benthic-pelagic coupling. In shallow coastal areas, bivalves are exposed to frequent disturbance and salinity stress that might negatively affect their activity and physiological performance; however, the mechanisms underlying these effects are not fully understood. We investigated the effects of osmotic stress (low and fluctuating salinity) and repeated burrowing on aerobic and contractile capacity of the foot muscle (assessed by the activity of succinate dehydrogenase and myosin ATPase) as well as the levels of organic osmolytes (free amino acids) and biochemical markers of protein synthesis and proteolysis in key osmoregulatory and energy storing tissues (gills and hepatopancreas, respectively) in a common bioturbator, the soft shell clam Mya arenaria. Our findings indicate that exhaustive exercise and osmotic stress interactively affect whole-body protein homeostasis and functional capacity of the foot muscle in soft shell clams which might contribute to reduced burrowing activity of bivalve bioturbators in osmotically challenging environments such as estuaries and shallow coastal zones.

The ubiquitous freshwater cyanobacterium Microcystis is remarkably successful, showing a high tol... more The ubiquitous freshwater cyanobacterium Microcystis is remarkably successful, showing a high tolerance against fluctuations in environmental conditions. It frequently forms dense blooms which can accumulate significant amounts of the hepatotoxin microcystin, which plays an extracellular role as an infochemical but also acts intracellularly by interacting with proteins of the carbon metabolism, notably with the CO2 fixing enzyme RubisCO. Here we demonstrate a direct link between external microcystin and its intracellular targets. Monitoring liquid cultures of Microcystis in a diel experiment revealed fluctuations in the extracellular microcystin content that correlate with an increase in the binding of microcystin to intracellular proteins. Concomitantly, reversible relocation of RubisCO from the cytoplasm to the cell’s periphery was observed. These variations in RubisCO localization were especially pronounced with cultures grown at higher cell densities. We replicated these effects...

Among prokaryotes, cyanobacteria have an exclusive position due to the fact that they perform oxy... more Among prokaryotes, cyanobacteria have an exclusive position due to the fact that they perform oxygenic photosynthesis. Cyanobacteria substantially differ from other bacteria in further aspects, e.g. they evolved a plethora of unique regulatory mechanisms to control primary metabolism. This is exemplified by the regulation of glutamine synthetase (GS) via small proteins termed inactivating factors (IFs). Here we reveal another small, 51 amino acid protein, which is encoded by the ssr0692 gene, to regulate flux into the ornithine-ammonia cycle (OAC), the key hub of cyanobacterial nitrogen stockpiling and remobilization. This regulation is achieved by the interaction with the central carbon/nitrogen control protein PII, which commonly controls the entry into the OAC by activating the key enzyme of arginine synthesis, N-acetyl-L-glutamate kinase (NAGK). We suggest that Ssr0692 competes with NAGK for PII binding and thereby prevents NAGK activation, which in turn lowers arginine synthesi...

Plant Cell and Environment, Jun 2, 2023

bioRxiv (Cold Spring Harbor Laboratory), Apr 3, 2022

Methods in molecular biology, 2017

Journal of Experimental Botany, Dec 8, 2021

Science of The Total Environment

Plants, 2022

Glycine decarboxylase controls photosynthesis and plant growth

Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences freque... more Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences frequent changes in salinity. They are often exposed to mechanical disturbances (like wave, currents, storms) forcing them to bury deeper into the sediment to get a better foothold. In nature, these stressors often occurs simultaneously. Osmotic stress negatively affects the burial activity and the physiological performances of soft shell clam, Mya arenaria; however, the mechanism behind this is still unknown. In this dataset we present the combined effect of osmotic stress and repeated burrowing on the concentration on different amino acids and short chain organic acids in the whole body tissue of Mya arenaria.

Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences freque... more Bioturbators (such as bivalves, worms, polychaetes), living in a coastal area, experiences frequent changes in salinity. They are often exposed to mechanical disturbances (like wave, currents, storms) forcing them to bury deeper into the sediment to get a better foothold. In nature, these stressors often occurs simultaneously. Osmotic stress negatively affects the burial activity and the physiological performances of soft shell clam, Mya arenaria; however, the mechanism behind this is still unknown. In this dataset we present the combined effect of osmotic stress and repeated burrowing on the trypsin- and chymotrypsin-like proteasomal and lysosomal activity in gill tissue and digestive gland of Mya arenaria.

eLife, 2022