Biology subjects

Mühlbauer, S.

Publications and source records attributed to Mühlbauer, S..

5 recordsLinked to original sources

bioRxiv2026

The Conserved N-Terminal Extension of AtKEA1 Is Largely Dispensable for Plastid Function but Contributes to Potassium Homeostasis

Members of the K efflux antiporter (KEA) family fulfill key roles in plastids and the endomembrane system. Plants and green algae possess at least one KEA mediating K/H exchange across the plastid inner envelope (IE) membrane. Recently, IE KEAs were shown to be essential for plastid gene expression (PGE), chloroplast development, and photosynthesis. Plants lacking these antiporters exhibit reduced stromal protein synthesis and accumulation of unprocessed rRNA precursors. KEA proteins comprise a conserved monovalent cation/proton antiporter 2 (CPA2) domain and a regulatory K transport and NAD-binding (KTN) domain. IE KEAs are distinguished by an additional [~]500-amino-acid N-terminal extension containing a coiled-coil (CC) domain embedded within a largely intrinsically disordered region (IDR). Intrigued by this unusual architecture, we performed phylogenetic analyses, revealing that this N-terminal fusion arose early and has been conserved throughout the green lineage. We then investigated the oligomeric state, native distribution, and function of the N-terminal domain. Using Arabidopsis thaliana, we found that IE KEAs localize to discrete clusters within the inner envelope membrane and assemble into complexes of approximately 600 kDa. Finally, complementary approaches using a functional KEA1 variant lacking the core N-terminal domains (KEA1{Delta}N) indicate that this extension plays a regulatory rather than an essential role. Our findings uncover an evolutionarily ancient regulatory module that shapes the molecular organization and function of IE KEAs, advancing our understanding of plastid ion and pH homeostasis and plastid ribosome integrity. One-sentence summaryPlastid KEA1/2 proteins feature a unique N-terminal extension that modulates potassium transport activity in a yet unknown manner but is not essential for normal plant growth under ambient conditions.

plant biology↗

bioRxiv2025

Conserved and Lineage-Specific Roles of KEA-Mediated Ion Homeostasis in Chlamydomonas

In Arabidopsis thaliana, seamless plastid gene expression and development depend on finely balanced ion homeostasis across the inner envelope (IE) membrane, maintained by the K/H antiporters AtKEA1/2. To assess whether these functions are retained across mono- and polyplastidic representatives of the green lineage, we studied CrKEA1, the sole IE KEA homolog in the unicellular alga Chlamydomonas reinhardtii. Using CRISPR/Cas9, we generated a Cr-kea1 knockout mutant that exhibits impaired photoautotrophic growth, chloroplast deformation, and photoinhibition. Transcriptomics revealed strong induction of ribosome biogenesis genes and reduced abundance of transcripts associated with cell and plastid division. Further RNA analyses confirmed defects in stromal rRNA maturation of Cr-kea1, paralleling observations from Arabidopsis kea1kea2 mutants. Expression of CrKEA1 in Arabidopsis rescued growth and rRNA maturation in At-kea1kea2, demonstrating functional continuity after the ancient divergence between the two lineages. Cross-species transcriptomic comparisons further revealed that IE KEA loss elicits both shared and species-specific transcriptional responses: PhANG repression was conserved between algae and plants, whereas activation of the chloroplast unfolded protein response (cpUPR) and reduced expression of genes tied to cell-cycle and plastid fission occurred only in Chlamydomonas. Single-cell time-lapse imaging confirmed that Cr-kea1 exhibits an increased frequency of aberrant cytokinesis, unequal division, and division failure. Our findings demonstrate that while IE KEA transporters fulfill conserved roles in maintaining the conditions for plastid gene expression, their integration into broader cellular networks has diverged between unicellular chlorophytes and embryophytes (land plants). This underscores a lineage-dependent tuning of plastid-nucleus communication shaped by organismal complexity and plastid number. One-sentence summaryDisruption of KEA-mediated chloroplast ion homeostasis in Chlamydomonas reinhardtii reveals conserved and lineage-specific control of plastid rRNA processing and cell cycle progression.

plant biology↗

bioRxiv2025

Cell wall integrity and elicitor peptide signaling modulate antimicrobial defense in Arabidopsis via jasmonic acid

Plant cell walls constitute dynamic barriers that are essential for defense against pathogens. The receptor kinase THESEUS1 (THE1) monitors cell wall integrity (CWI) and contributes to pathogen resistance in Arabidopsis, but the underlying mechanisms remain unclear. Here we show that THE1-dependent CWI signaling induces accumulation of the antimicrobial metabolite camalexin upon cell wall damage (CWD) caused by cellulose biosynthesis inhibition or fungal infection. CWD alters THE1 plasma membrane nanodomain organization and involves calcium signaling components that modulate camalexin production. Induction of camalexin requires jasmonic acid (JA)-dependent expression of the transcription factors MYB47 and MYB95. In line with its antagonistic function on CWI signaling, the plant elicitor peptide Pep3 suppresses camalexin biosynthesis downstream of THE1 by inhibiting JA-dependent pathways. Our findings reveal a regulatory network where CWI and Pep3 signaling modulate antimicrobial defense via JA-mediated camalexin production. This network requires independent CWD-induced pathways, providing insights into how plants balance defense activation and suppression in response to cell wall stress.

plant biology↗

bioRxiv2025

Expression levels of the Band-7 protein FLOTILLIN modulate salt tolerance, growth and development in the moss Physcomitrium patens

The Band-7 proteins, known as FLOTILLINs (FLOT), are present at the plasma membranes of most land plants. They function in clathrin-independent endocytosis and contribute to nodule formation following symbiotic infections. This study reveals that the single FLOT variant in Physcomitrium patens is located at the thylakoid membranes in chloroplasts, serving an unanticipated function. Phenotypic analysis of knockout and overexpression lines demonstrates that PpFLOT overexpression significantly impairs the high salinity tolerance of P. patens. Additionally, liquid protonema cultures of PpFLOT-OEX lines exhibited a distinct color change due to necrotic events and developed brachycyte-like cells. These changes correlate with the strength of PpFLOT expression and do not occur when these lines are cultivated on solid medium. Our study found that PpFLOT-OEX lines display increased chlorophyll and H2O2 production. We also discovered that PpFLOT is regulated by ABA and light, and its high expression can potentially affect retrograde signaling. Metabolomics and proteomics analyses revealed changes in the pigment and lipid composition as well as differentially accumulated proteins in PpFLOT mutant lines. We also observed changes in the expression of ion-transport related genes, accumulation of lipids crucial during pathogen defense, and differentially accumulated proteins taking part in multiple metabolomic pathways. Consequently, our study suggests a novel role for chloroplastic PpFLOT in plant terrestrialization, as it is putatively involved in Ca2+ and reactive oxygen species (ROS) signaling in response to abiotic and biotic stress, along with the light-dependent regulation of chlorophyll biosynthesis.

plant biology↗

bioRxiv2023

Differentiation trajectories of the Hydra nervous system reveal transcriptional regulators of neuronal fate

Hydra vulgaris, a cnidarian with a simple nerve net, is an emerging model for developmental, regenerative, and functional neuroscience. Its genetic tractability and capacity for whole-system imaging make it well suited for studying neuron replacement, regeneration, and neural circuit function. Here, we present the most comprehensive molecular and spatial characterization of the H. vulgaris nervous system to date. Using single-cell RNA sequencing, we identified eight neuron types, each defined by distinct neuropeptide expression, and further resolved these into fifteen transcriptionally distinct subtypes with unique spatial distributions and morphologies. To investigate the gene regulatory networks underlying neuronal differentiation, we applied trajectory inference, identified key transcription factors, and performed ATAC-seq on sorted neurons to map chromatin accessibility. All datasets are available through an interactive, user-friendly web portal to support broad use by the research community. Together, these resources provide a foundation for uncovering molecular mechanisms that govern nervous system development, homeostasis, and regeneration in H. vulgaris. Summary StatementHydra vulgaris is a model for regenerative and functional neuroscience. This study identifies fifteen neuron subtypes using scRNA-seq, maps spatial distributions, explores regulatory mechanisms, and provides an accessible web portal.

developmental biology↗