Biology subjects

Buschmann, H.

Publications and source records attributed to Buschmann, H..

6 recordsLinked to original sources

bioRxiv2025

The Spirogyra genome: signatures of shared and divergent division and differentiation

Zygnematophytes emerged as the unexpected closest algal relatives of land plants despite their simple body plans, raising questions about the morphogenetic toolkit present in the last common ancestor of land plants and algae. Genomic analyses have revealed that zygnematophytes are cellular giants, sharing homologous frameworks for several phytohormones, secondary metabolites, and key morphogenetic and transcriptional regulatory processes. Zygnematophytes fall into five orders, each of which has charted its own evolutionary path. Here, we have sequenced a contiguous genome of Spirogyra pratensis, the eponymous representative of Spirogyrales and a classical model system for evolutionary cell biology in the green lineage. Building on this genome, we transcriptionally profiled the tractable life cycle of Spirogyra and its responses to a bifactorial gradient of light and temperature. Our data highlight the activation of quiescence and homeostatic programs. Yet what stands out most in Spirogyra is its spiral chloroplast--undulating intracellularly and abscising during mixed phragmoplast formation and furrowing. Leveraging the genome in tandem with co-expression network analyses, we describe the molecular underpinnings of the unique cytokinetic processes that govern both cell and plastid division. We find that Spirogyra deploys a molecular program characteristic of Phragmoplastophyta, yet lacks the deeply conserved plastid division machinery found in other archaeplastid plastids.

plant biology↗

bioRxiv2023

Phylogenomic insights into the first multicellular streptophyte

Streptophytes are best known as the clade containing the teeming diversity of embryophytes (land plants)1-4. Next to embryophytes are however a range of freshwater and terrestrial algae that bear important information on the emergence of key traits of land plants. Among these, the Klebsormidiophyceae stand out. Thriving in diverse environments--from mundane (ubiquitous occurrence on tree barks and rocks) to extreme (from the Atacama Desert to the Antarctic); Klebsormidiophyceae can exhibit filamentous body plans and display remarkable resilience as colonizers of terrestrial habitats5,6. Currently, the lack of a robust phylogenetic framework for the Klebsormidiophyceae hampers our understanding of the evolutionary history of these key traits. Here, we conducted a phylogenomic analysis utilizing advanced models that can counteract systematic biases. We sequenced 24 new transcriptomes of Klebsormidiophyceae and combined them with 14 previously published genomic and transcriptomic datasets. Using phylogenomic analysis built on 420 loci and sophisticated models, we establish a novel phylogenetic structure, dividing the six distinct genera of Klebsormidiophyceae in a novel four-order-system, with deep divergences more than 898, 765, and 734 million years ago. The reconstruction of ancestral states for habitat suggests an evolutionary history of multiple transitions between terrestrial-aquatic habitats, with Klebsormidiales having conquered land earlier than embryophytes. Focusing on the body plan of the last common ancestor of Klebsormidiophyceae, we postulate it was likely filamentous whereas the sarcinoids and unicells in Klebsormidiophyceae are likely derived states. Our data reveal that the first multicellular streptophytes likely lived more than 900 million years ago.

evolutionary biology↗

bioRxiv2023

Chromosome-level genomes of multicellular algal sisters to land plants illuminate signaling network evolution

The filamentous and unicellular algae of the class Zygnematophyceae are the closest algal relatives of land plants. Inferring the properties of the last common ancestor shared by these algae and land plants allows us to identify decisive traits that enabled the conquest of land by plants. We sequenced four genomes of filamentous Zygnematophyceae (three strains of Zygnema circumcarinatum and one strain of Z. cylindricum) and generated chromosome-scale assemblies for all strains of the emerging model system Z. circumcarinatum. Comparative genomic analyses reveal expanded genes for signaling cascades, environmental response, and intracellular trafficking that we associate with multicellularity. Gene family analyses suggest that Zygnematophyceae share all the major enzymes with land plants for cell wall polysaccharide synthesis, degradation, and modifications; most of the enzymes for cell wall innovations, especially for polysaccharide backbone synthesis, were gained more than 700 million years ago. In Zygnematophyceae, these enzyme families expanded, forming co-expressed modules. Transcriptomic profiling of over 19 growth conditions combined with co-expression network analyses uncover cohorts of genes that unite environmental signaling with multicellular developmental programs. Our data shed light on a molecular chassis that balances environmental response and growth modulation across more than 600 million years of streptophyte evolution. HIGHLIGHTSO_LIGenomes of four filamentous algae (Zygnema) sisters to land plants C_LIO_LIZygnema are rich in genes for multicellular growth and environmental acclimation: signaling, lipid modification, and transport C_LIO_LICell wall innovations: diversification of hexameric rosette cellulose synthase in Zygnematophyceae C_LIO_LICo-expression networks reveal conserved modules for balancing growth and acclimation C_LI

evolutionary biology↗

bioRxiv2022

Environmental gradients reveal stress hubs predating plant terrestrialization

Plant terrestrialization brought forth the land plants (embryophytes). Embryophytes account for most of the biomass on land and evolved from streptophyte algae in a singular event. Recent advances have unraveled the first full genomes of the closest algal relatives of land plants; among the first such species was Mesotaenium endlicherianum. Here, we used fine-combed RNAseq in tandem with photophysiological assessment on Mesotaenium exposed to a continuous range of temperature and light cues. Our data establish a grid of 42 different conditions, resulting in 128 transcriptomes and ~1.5 Tbp (~9.9 billion reads) of data to study combinatory effects of stress response using clustering along gradients. We describe major hubs in genetic networks underpinning stress response and acclimation in the molecular physiology of Mesotaenium. Our data suggest that lipid droplet formation, plastid and cell wall-derived signals denominate molecular programs since more than 600 million years of streptophyte evolution--before plants made their first steps on land.

evolutionary biology↗

bioRxiv2022

A phylogenomically informed five-order system for the closest relatives of land plants

The evolution of streptophytes had a profound impact on life on Earth. They brought forth those photosynthetic eukaryotes that today dominate the macroscopic flora: the land plants (Embryophyta) [1]. There is convincing evidence that the unicellular/filamentous Zygnematophyceae--and not the morphologically more elaborate Coleochaetophyceae or Charophyceae--are the closest algal relatives of land plants [2, 3, 4, 5, 6]. Despite the species richness (>4,000), wide distribution, and key evolutionary position of the zygnematophytes, their internal phylogeny remains largely unresolved [7, 8]. There are also putative zygnematophytes with interesting body plan modifications (e.g., filamentous growth) whose phylogenetic affiliations remain unknown. Here, we studied a filamentous green alga (strain MZCH580) from an Austrian peat bog with central or parietal chloroplasts that lack discernible pyrenoids. It represents Mougeotiopsis calospora PALLA, an enigmatic alga that was described more than 120 years ago [9], but never subjected to molecular analyses. We generated transcriptomic data of M. calospora strain MZCH580, and conducted comprehensive phylogenomic analyses (326 nuclear loci) for 46 taxonomically diverse zygnematophytes. Strain MZCH580 falls in a deep-branching zygnematophycean clade together with some unicellular species, and thus represents a formerly unknown zygnematophycean lineage with filamentous growth. Our well-supported phylogenomic tree lets us propose a new five-order system for the Zygnematophyceae, and provides evidence for at least five independent origins of true filamentous growth in the closest algal relatives of land plants. This phylogeny provides a robust and comprehensive framework for performing comparative analyses and inferring the evolution of cellular traits and body plans in the closest relatives of land plants.

evolutionary biology↗

bioRxiv2020

Split-HaloTag Imaging Assay for in vivo 3D-Microscopy and Subdiffractional Analyses of Protein-Protein Interactions

An ever-increasing number of intracellular multi-protein networks have been identified in plant cells. Split-GFP based protein-protein interaction assays combine the advantages of in vivo interaction studies in a native environment with additional visualisation of protein complex localisation. Due to its simple protocols, it has become one of the most frequently used methods. However, standard fluorescent proteins entail several drawbacks for sophisticated microscopy. With the HaloTag(R) system, these drawbacks can be overcome as this reporter forms covalent irreversible bonds with synthetic photostable fluorescent ligands. Dyes can be used in adjustable concentrations and are suitable for advanced microscopy methods. Therefore, we established the Split-HaloTag(R) imaging assay in plants which is based on the reconstitution of a functional HaloTag(R) protein upon protein-protein interaction and subsequent covalent binding of an added fluorescent ligand. Its suitability and robustness were demonstrated using well-characterised interactions as an example for protein-protein interaction at cellular structures: the molybdenum cofactor biosynthesis complex anchoring to filamentous actin. Additionally, a specific interaction was visualised with subdiffractional polarisation microscopy in a more distinctive manner as example for sophisticated imaging. Split-GFP and Split-HaloTag(R) can complement one another as Split-HaloTag(R) represents an alternative option and an addition to the large toolbox of in vivo methods. Therefore, this promising new Split-HaloTag(R) imaging assay provides a unique and sensitive approach for more detailed characterization of protein-protein interaction with specific microscopic techniques such as 3D-imaging, single molecule tracking and super-resolution microscopy.

plant biology↗