Biology subjects

Mühlhaus, T.

Publications and source records attributed to Mühlhaus, T..

5 recordsLinked to original sources

bioRxiv2026

Loss of ELM1B impairs mitochondrial fission, matrix redox state and stress tolerance in Physcomitrium patens

Mitochondria are endosymbiont-derived organelles that play a central role in cellular metabolism, energy production and stress responses. While single mitochondria represent functional units, they continuously exchange their contents through fusion and fission, facing stress conditions as a dynamic population. To date, it remains largely unknown how stress alters mitochondrial dynamics in plants and how altered dynamics affect mitochondrial properties and plant stress resilience. Here, we investigate mitochondrial dynamics in response to oxidative stress in the non vascular model plant Physcomitrium patens. By creating mutants with impaired mitochondrial fission in different reporter lines for mitochondrial parameters, we additionally analyse effects of chronic changes to mitochondrial population dynamics. We found that Mito-Paraquat (MtPQ) treatment increased the glutathione redox potential EGSH in mitochondria, the cytosol and chloroplasts, as monitored via roGFP2-based genetically encoded biosensors. Mitochondria elongated within hours and showed a concomitant and heterogenous increase of matrix EOSred, that we propose as a marker for matrix protein damage. Mitochondrial fission mutants lacking PpELM1B (ELONGATED MITOCHONDRIA) displayed distinct changes of mitochondrial morphology parameters as determined by automated 3D-segmentation and feature mapping (MorphoMapper) of confocal z-stacks. Elongated mitochondria in Ppelm1bge lines showed an oxidative matrix EGSH shift and increased matrix EOSred while matrix mixing still occurred, albeit at the same slow rate as in wildtype, within days. Macroscopically, Ppelm1bge lines displayed reduced growth, decreased respiration, and a higher sensitivity to oxidative stress. Our results show that plant mitochondrial morphology and physiological parameters specifically shift in response to stress and impaired fission. Mitochondrial fission is vital to maintain a healthy mitochondrial population that sustains plant oxidative stress tolerance.

plant biology↗

bioRxiv2024

Complexome profiling of the Chlamydomonas psb28 mutant reveals THYLAKOID ENRICHED FRACTION 5 as an early photosystem II assembly factor

Several auxiliary factors are required for the assembly of photosystem (PS) II, one of which is Psb28. While the absence of Psb28 in cyanobacteria has little effect on PSII assembly, we show here that the Chlamydomonas psb28-null mutant is severely impaired in PSII assembly, showing drastically reduced PSII supercomplexes, dimers and monomers, while overaccumulating RCII, CP43mod and D1mod. The mutant had less PSI and more Cytb6f and showed fewer thylakoid stacks and distorted chloroplast morphology. Complexome profiling of the psb28 mutant revealed that TEF5, the homolog of Arabidopsis PSB33/LIL8, co-migrated particularly with RCII. TEF5 also interacted with PSI. A Chlamydomonas tef5 null mutant is also severely impaired in PSII assembly and overaccumulates RCII and CP43mod. RC47 was not detectable in the light-grown tef5 mutant. Our data suggest a possible role for TEF5 in facilitating the assembly of CP47mod into RCII. Both the psb28 and tef5 mutants exhibited decreased synthesis of CP47 and PsbH, suggesting negative feedback regulation possibly exerted by the accumulation of RCII and/or CP43mod in both mutants. The strong effects of missing auxiliary factors on PSII assembly in Chlamydomonas suggest a more effective protein quality control system in this alga than in land plants and cyanobacteria. One-sentence summaryThe Chlamydomonas psb28 mutant is severely impaired in PSII assembly which via complexome profiling allowed identifying TEF5 as a novel PSII assembly factor that likely facilitates CP47 assembly. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (https://academic.oup.com/plcell/pages/General-Instructions) is: Michael Schroda (m.schroda@rptu.de).

plant biology↗

bioRxiv2021

Complexome profiling on the lpa2 mutant reveals insights into PSII biogenesis and new PSII associated proteins

We have identified the homolog of LOW PSII ACCUMULATION 2 (LPA2) in Chlamydomonas. A Chlamydomonas lpa2 mutant grew slower in low light and was hypersensitive to high light. PSII maximum quantum efficiency was reduced by 38%. Synthesis and stability of newly made PSII core subunits D1, D2, CP43, and CP47 were not impaired. Complexome profiling revealed that in the mutant CP43 was reduced to [~]23%, D1, D2, and CP47 to [~]30% of wild-type levels, while small PSII core subunits and components of the oxygen evolving complex were reduced at most by factor two. PSII supercomplexes, dimers, and monomers were reduced to 7%, 26%, and 60% of wild-type levels, while RC47 was increased [~]6-fold. Our data indicate that LPA2 acts at a step during PSII assembly without which PSII monomers and especially further assemblies become intrinsically unstable and prone to degradation. Levels of ATP synthase and LHCII were 29% and 27% higher in the mutant than in the wild type, whereas levels of the cytochrome b6f complex were unaltered. While the abundance of PSI core subunits and antennae hardly changed, LHCI antennae were more disconnected in the lpa2 mutant, presumably as an adaptive response to reduce excitation of PSI. The disconnection of LHCA2,9 together with PSAH and PSAG was the prime response, but independent and additional disconnection of LHCA1,3-8 along with PSAK occurred as well. Finally, based on co-migration profiles, we identified three novel putative PSII associated proteins with potential roles in regulating PSII complex dynamics, assembly, and chlorophyll breakdown. One-sentence summaryWe provide evidence that the Chlamydomonas LPA2 homolog acts at a step in PSII biogenesis without which PSII monomers and further assemblies become unstable and prone to degradation.

plant biology↗

bioRxiv2020

Vernalization alters sugar beet (Beta vulgaris) sink and source identities and reverses phloem translocation from taproots to shoots

During vegetative growth, biennial sugar beets maintain a steep gradient between the shoot (source) and the sucrose-storing taproot (sink). To shift from vegetative to generative growth, they require a chilling phase, called vernalization. Here, we studied sugar beet sink-source dynamics upon cold temperature-induced vernalization and revealed a pre-flowering taproot sink to source reversal. This transition is induced by transcriptomic and functional reprogramming of sugar beet tissue, resulting in a reversal of flux direction in long distance transport system, the phloem. As a key process for this transition, vacuolar sucrose importers and exporters, BvTST2;1 and BvSUT4, are oppositely regulated, leading to re-mobilization of sugars from taproot storage vacuoles. Concomitant changes in the expression of floral regulator genes suggest that the now deciphered processes are a prerequisite for bolting. Our data may thus serve dissecting metabolic and developmental triggers for bolting, which are potential targets for genome editing or breeding approaches.

plant biology↗

bioRxiv2019

Identification of chloroplast envelope proteins with critical importance for cold acclimation

The ability of plants to cope with cold temperatures relies on their photosynthetic activity. This already demonstrates that the chloroplast is of utmost importance for cold acclimation and acquisition of freezing tolerance. During cold acclimation, the properties of the chloroplast change markedly. To provide the most comprehensive view of the protein repertoire of chloroplast envelope, we analysed this membrane system in Arabidopsis thaliana using MS-based proteomics. Profiling chloroplast envelope membranes was achieved by a cross comparison of protein intensities across plastid and the enriched membrane fraction both under normal and cold conditions. Multivariable logistic regression models the probabilities for the classification problem to address envelop localization. In total, we identified 38 envelope membrane intrinsic or associated proteins exhibiting altered abundance after cold acclimation. These proteins comprise several solute carries, such as the ATP/ADP antiporter NTT2 (substantially increased abundance) or the maltose exporter MEX1 (substantially decreased abundance). Remarkably, analysis of the frost recovery of ntt loss-of-function and mex1 overexpressor mutants confirmed that the comparative proteome is well suited to identify novel key factors involved in cold acclimation and acquisition of freezing tolerance. Moreover, for proteins with known physiological function we propose scenarios explaining their possible role in cold acclimation. Furthermore, spatial proteomics introduces a novel layer of complexity and enabled the identification of proteins differentially localized at the envelope membrane under the changing environmental regime.

plant biology↗