Biology subjects

Armbruster, U.

Publications and source records attributed to Armbruster, U..

5 recordsLinked to original sources

bioRxiv2025

Advanced illumination-imaging reveals photosynthesis-triggered pH, ATP and NAD redox signatures across plant cell compartments

Photosynthesis provides energy and organic substrates to most life. In plants, photosynthesis dominates chloroplast physiology but represents only a fraction of the tightly interconnected metabolic network that spans the entire cell. Here, we explore how photosynthetic activity affects energy physiology within and beyond the chloroplast. We developed a new standard for the live-monitoring of subcellular energy physiology by combining confocal imaging of genetically encoded fluorescent protein biosensors with advanced on-stage illumination technology to investigate pH, MgATP2- and NADH/NAD+ dynamics at dark-light transitions in Arabidopsis mesophyll cells. Our findings reveal a stromal alkalinization signature induced by photosynthetic proton pumping, extending to the cytosol and mitochondria as an alkalinization wave. Photosynthesis leads to increased MgATP2- levels in both the stroma and cytosol. Additionally, we observed reduction of the NAD pool driven by photosynthesis-derived electron export. Arabidopsis lines defective in chloroplast NADP- and mitochondrial NAD-dependent malate dehydrogenases show more reduced cytosolic NAD redox status even in darkness, highlighting the involvement of chloroplasts and mitochondria in shaping cytosolic redox metabolism via malate metabolism. Our study sets a novel methodological standard for precision live-monitoring of photosynthetic cell physiology. Applying this technology reveals signatures of photosynthetic physiology within and beyond the chloroplast with unprecedented resolution. Those signatures link photosynthetic activity and the fundamental biochemical functions of phototrophic cells. Significance statementBy applying novel live microscopy monitoring using fluorescent protein biosensors in plant cells, we reveal that dark-light transitions trigger profound re-orchestration of subcellular pH, ATP and NAD redox physiology not limited to chloroplasts but extending into the cytosol and the mitochondria.

plant biology↗

bioRxiv2025

Cysteine signaling in plant pathogen response

The amino acid cysteine is the precursor for a wide range of sulfur-containing functional molecules in plants, including enzyme cofactors and defense compounds. Due to its redox active thiol group cysteine is highly reactive. Synthesis and degradation pathways are present in several subcellular compartments to adjust the intracellular cysteine concentration. However, stress conditions can lead to a transient increase in local cysteine levels. Here we investigate links between cysteine homeostasis and metabolic signaling in Arabidopsis thaliana. The systemic proteome response to cysteine feeding strongly suggests that Arabidopsis seedlings interpret accumulation of cysteine above a certain threshold as a signal for a biotic threat. Cysteine supplementation of Arabidopsis plants via the roots increases their resistance to the hemibiotrophic bacterium Pseudomonas syringae confirming the protective function of the cysteine induced defense pathways. Analysis of mutant plants reveals that the balance of cysteine synthesis between the cytosol and organelles is crucial during Arabidopsis immune response to Pseudomonas syringae. The induction profile of pathogen responsive proteins by cysteine provides insight into potential modes of action. Our results highlight the role of cysteine as a metabolic signal in the plant immune response and add evidence to the emerging concept of intracellular organelles as important players in plant stress signaling.

plant biology↗

bioRxiv2023

A congestion downstream of PSI causes the over-reduction of the electron transport chain in pgr5 independent of membrane energization

The thylakoid protein Proton Gradient Regulation5 (PGR5) is thought to be a key component of cyclic electron flux around photosystem I. The pgr5 mutant is characterized by impaired proton motive force (pmf) formation across the thylakoid membrane, decreased photoprotective non-photochemical quenching (NPQ), and an over-reduction of the PSI acceptor side. This over-reduction has been attributed to impaired photosynthetic control, which down-regulates plastoquinol re-oxidation at the cytochrome b6f complex when the lumen is strongly acidified. Here, using the cgl160 ATP synthase assembly mutant, we show that in cgl160 pgr5 double mutants, both the pmf across the thylakoid membrane and NPQ are fully restored to wild-type levels. However, the acceptor-side limitation of PSI in the double mutants stays comparable to the single pgr5 mutant. This demonstrates that impaired photosynthetic control is not causal for the over-reduction of the PSI acceptor side in pgr5. Instead, we show that both in pgr5 and the clg160 pgr5 mutants, the entire high-potential chain from cytochrome f to PSI remains strongly reduced in high light. This leads to insufficient oxidizing power for plastoquinol re-oxidation by the cytochrome b6f complex, thus impairing pmf formation. We conclude that PGR5 plays a critical role in electron partitioning downstream of PSI.

plant biology↗

bioRxiv2023

A eukaryote-specific factor mediates an early step in the assembly of plant photosystem II

ABSTRACTThe initial step of oxygenic photosynthesis is the thermodynamically challenging extraction of electrons from water and the release of molecular oxygen. This light-driven process, which is the basis of life on Earth, is catalyzed by the photosystem II (PSII) within the thylakoid membrane of photosynthetic organisms. The biogenesis of PSII requires a controlled step-wise assembly process of which the early steps are considered to be highly conserved between plants and their cyanobacterial progenitors. This assembly process involves auxiliary proteins, which are likewise conserved. In the present work, we show that in plants, the early assembly step, in which the PSII reaction center (RC) is associated with the intrinsic antenna protein CP47 to form the RC47 intermediate, is facilitated by a novel eukaryote-exclusive assembly factor. This factor, we named DEAP2 for DECREASED ELECTRON TRANSPORT AT PSII, works in concert with the conserved PAM68 assembly factor. The deap2 and pam68 mutants showed similar defects in PSII accumulation and assembly of the RC47 intermediate. The combined lack of both proteins results in a loss of functional PSII and the inability of plants to grow photoautotrophically on soil. While overexpression of DEAP2 partially rescued the pam68 PSII accumulation phenotype, this effect was not reciprocal. DEAP2 accumulates at 20-fold higher levels than PAM68, together suggesting that both proteins have distinct functions. In summary, our results uncover eukaryotic adjustments to the PSII assembly process, which involve the addition of DEAP2 for the rapid progression from RC to RC47.

plant biology↗

bioRxiv2022

The K+ exchange antiporter 3 senses the chloroplast energy status to synchronize photosynthesis

Plant photosynthesis contains two functional modules, the light-driven reactions in the thylakoid membrane and the carbon-fixing reactions in the chloroplast stroma. In nature, light availability for photosynthesis often undergoes massive and rapid fluctuations. Efficient and productive use of such variable light supply requires an instant crosstalk and rapid synchronization of both functional modules. Here, we show that this communication involves the stromal exposed regulatory C-terminus (RCT) of the thylakoid K+-exchange antiporter KEA3. RCT-mediated control of KEA3 contributes to the balance between light capture and photoprotection. By combining in silico, in vitro, and in vivo approaches, we demonstrate that the RCT senses the energy state of the chloroplast in form of both, phosphorylation and redox potential, in a pH-dependent manner and regulates KEA3 activity in response. Together our data pinpoint a regulatory feedback loop by which the stromal energy state orchestrates light capture and photoprotection via KEA3.

plant biology↗