Biology subjects

Kunz, C. F.

Publications and source records attributed to Kunz, C. F..

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↗

bioRxiv2026

Homologous ABA-independent kinase tracks coalesced into osmotic stress circuits during plant terrestrialization

Land plants possess a unique system for responding to environmental stressors. How this system evolved during plant terrestrialization remains one of the major questions in plant evolutionary biology. To retrace this process, it is essential to study both land plants and their closest algal relatives, the zygnematophytes. Using the single-celled zygnematophyte Mesotaenium, we integrated physiological stress experiments with phosphoproteomics, genome-wide transcription factor binding analyses, and protein-protein interaction studies to investigate the architecture of a key stress response pathway: the signaling cascade homologous to the plant abscisic acid (ABA)-mediated pathway. Our results highlight the roles of histidine kinases (HKs) and calcium-dependent protein kinases (CDPKs) in osmotic stress signaling. Focusing on SnRK2 and ABF, key components at the downstream end of the canonical ABA signaling pathway, we provide evidence that ABF plays a central role in osmotic stress responses even in the absence of ABA. Together, our data reveal the coordinated action of parallel functional modules that were likely integrated into the ABA response cascade during plant terrestrialization.

evolutionary biology↗

bioRxiv2026

A deep genetic structure phylogenomically frames the closest algal relatives of land plants

To discern the nature of the closest streptophyte algal relatives of land plants (embryophytes) is a major question in the field of plant evolutionary biology; discerning that nature is essential for our ability to infer the last common ancestor of embryophytes and algae, allowing to retrace the adaptations that ushered in the conquest of land by plants. Albeit initially coming as a surprise, all major phylogenomic efforts have concluded that the Zygnematophyceae are the algal sisters to land plants1-6. The Zygnematophyceae are the streptophyte algal class with the greatest species richness7 and while we now have ample genome information on a few select members of zygnematophytes8-13, our understanding of the genetic and genomic divergence as well as potential is limited by a lack of phylodiverse data that accounts for this diversity and integrates it into a phylogenomic framework. We here sequenced 43 new transcriptome datasets for the Zygnematophyceae and built a phylogenomic tree based on a total of 104 zygnematophyceaen transcriptomes and 2243 loci. We recover a deep genetic structure for the Zygnematophyceae, revealing that this algal class is ancient. Despite the deep split between Spirogyrales and their unicellular sister group Desmidiales, most Spirogyrales emerged after pronounced genetic divergence, accommodating the attainment of multicellularity and divergent traits such as unique cell and plastid division13. Overall, our data capture signatures of massive ancient radiations. Zygnematophyceae are characterized by deep genetic divergences that necessitated a phylodiverse sampling to be revealed, together with their vast evolutionary history, and to illuminate the nature of the algal progenitors of land plants.

evolutionary biology↗

bioRxiv2026

Chemodiverse cell systems responses to UV in an algal sister of land plants

Plant terrestrialization necessitated that a barrage of stressors had to be overcome1. Land plants use an integrated response network in adjusting their molecular physiology to terrestrial stressors2--one of the foremost being UV irradiance. The zygnematophytes are the closest streptophyte algal relatives of land plants3-5, are renowned for their resilience to UV stress6-8, and thus allow to glean key information for inferring the UV response toolkit of the earliest land plants9,10. Throughout streptophyte evolution, specialised metabolism radiated into creating diverse compounds used for responses to environmental challenges, such as sun-shielding compounds and antioxidants11-14. This includes UV-shielding compounds like flavonoids and coumarins but also the land plant specific polymer lignin, giving structural support in vascular plants15; homologs of the underpinning core pathway occur in streptophyte algae16. Here, we exposed the zygnematophyte Mesotaenium to UV-B irradiation and profiled its physiology, morphology, transcriptomics as well as metabolomic features. After UV-B exposure, cells showed rapid photophysiological responses and progressively growing terminal vacuoles. Our transcriptome data capture dynamic changes in gene expression of (i) core downstream responses such as genes homologous to phenol metabolic enzymes, photophysiological homeostats, and DNA repair factors; but also (ii) upstream components featuring key homologs of kinase-mediated signalling cascades, as well as light quality and abscisic acid-mediated signalling components. To scrutinize the acclimatory chassis, we created a metabolite feature database specifically for the Mesotaenium metabolome. Upon UV-B exposure, the metabolome displayed pronounced temporal shifts, with several phenolic features that accumulate along the stress-acclimation kinetics. Overall, we capture a chemodiverse response including various phenolics such as purpurogallin-like, methoxypsoralen-like derivatives and coumarins. Our data establish an integrated model for UV responses in the closest algal relatives of land plants, shedding light on the toolkit that allowed the progenitors of land plants to move out of a protective water column.

evolutionary biology↗

bioRxiv2025

Systems acclimation to osmotic stress in zygnematophyte cells

Zygnematophytes are the closest algal relatives of land plants. They hold key information to infer how the earliest land plants overcame the barrage of terrestrial stressors, prime of which is osmotic stress. Here, we applied two osmotic stressors on a unicellular and a multicellular representative of zygnematophytes and studied their response over a 25-hour time course generating 130, 60, and 30 of transcriptomic, proteomic, and metabolomic samples combined with photophysiology, sugar analysis, immunocytochemical glycoprotein analysis, and microscopy. Our data highlight a shared protein chassis that shows divergent responses with the same outcome: successful acclimation to osmotic challenges. We establish a model of how the algal sisters of land plants can overcome a prime stressor in the terrestrial habitat and highlight components of the plant terrestrialization toolkit.

evolutionary biology↗