Biology subjects

Delmans, M.

Publications and source records attributed to Delmans, M..

5 recordsLinked to original sources

bioRxiv2026

Marchantia stem cell maintenance and re-establishment are controlled by MpPIN1-mediated auxin transport and ARF signalling

Meristem organization in land plants depends on coordinated auxin distribution, transport and response, yet how these processes are integrated during vegetative growth of the gametophyte of non-seed plants remains poorly understood. Here, we describe dissection of the auxin network in the liverwort Marchantia polymorpha using a suite of endogenous and synthetic reporters. Quantitative imaging with the R2DII auxin response sensor revealed that the apical meristem is positioned at a stable auxin minimum, with auxin levels increasing toward differentiated tissues. This spatial configuration correlates with polar localization of the auxin efflux carrier MpPIN1 along the direction of auxin flux. Disruption of MpPIN1 alters auxin distribution and compromises tissue regeneration, but does not prevent initial meristem formation, indicating that PIN-mediated transport reinforces rather than defines stem-cell niche identity. Imaging of auxin response reporters and MpARF1 and MpARF2 knock-in reporters further revealed a constrained auxin response within the meristem, characterized by low auxin signalling, dependent on the inhibitory activity of MpARF2 in the stem cell zone. During regeneration, transient, oscillatory ARF dynamics were observed before stabilization of a new auxin minimum and re-establishment of normal meristem architecture. Together, our results are consistent with auxin responses in the Marchantia meristem being shaped by an incoherent feed-forward network topology that couples auxin flux, transcriptional constraint and niche permissiveness. This architecture provides a robust framework for stem-cell maintenance and re-establishment, revealing ancestral principles of meristem regulation in land plants. SUMMARY STATEMENTBy mapping hormone distribution at cellular resolution in the liverwort Marchantia polymorpha, we reveal fundamental principles governing how plants maintain and rebuild their stem cell niches.

Plant Biology↗

bioRxiv2024

Understanding Regeneration: investigating the apical notch and meristem re-emergence in Marchantia polymorpha

Meristems are the growth centres of plants, and fundamental in understanding plant development, morphogenesis and vegetative propagation. Across all plant groups, the phytohormone auxin controls meristem maintenance, represses the emergence of new meristems (apical dominance) and mediates cellular reprogramming when new meristems regenerate following removal of existing meristems. The liverwort Marchantia produces clonal propagules (gemmae) featuring two apical notches that develop into functional meristems. This presents a tractable experimental system to study meristem developmental biology. I used laser ablation microscopy to precisely disrupt cells in and around the developing pre-meristem in the apical notches of germinating gemma, finding that the first cell row is indispensable. Within this layer, a contiguous quorum of stem cells is required for activity. Apical notches reorientate in response to damage, demonstrating that the apical notch stem cells act as a communicating population. Feedback from the stem cell population is necessary to maintain notch activity and generate the notch apex. These experiments show communication between notches and regenerating meristems. The apical dominance signal represses cell division and requires both sources and sinks, features of auxin-mediated communication. Central regions of the gemma could transmit these apical dominance signals, but the tissues of the gemma periphery could not. I present a model of Marchantia gemma and apical notch organization, involving intra-, inter-and extra-notch communication. This provides a framework for further study of meristem formation, communication and maintenance in Marchantia and improving knowledge of plant meristems more generally. Significance StatementMeristems are the growth centres of plants. Understanding how meristems function, how existing meristems stop new meristems emerging (apical dominance) and how cellular reprogramming regenerates meristems is central to understanding plant development. The model plant Marchantia offers a streamlined system whose evolutionary position makes its biology relevant to all plants. Marchantia apical notches display proliferative, regenerative and dominance behaviour typical of meristems. I used laser ablation to precisely disrupt cells in and around the developing pre-meristematic apical notch of the germinating Marchantia gemma, producing an improved model of Marchantia apical notch organization involving intra-and inter-notch communication characteristic of the phytohormone auxin. This will inform future Marchantia research and provides a simplified experimental framework to study more complex meristematic processes.

plant biology↗

bioRxiv2023

Mapping the landscape of transcription factor promoter activity during vegetative development in Marchantia

Transcription factors (TFs) are essential for the regulation of gene expression and cell fate determination. Characterising the transcriptional activity of TF genes in space and time is a critical step towards understanding complex biological systems. The vegetative gametophyte meristems of bryophytes share some characteristics with the shoot-apical meristems of flowering plants. However, the identity and expression profiles of TFs associated with gametophyte organization are largely unknown. With only [~]450 TF genes, Marchantia polymorpha is an outstanding model system for plant systems biology. We have generated a near-complete collection of promoter elements derived from Marchantia TF genes. We experimentally tested in planta reporter fusions for all the TF promoters in the collection and systematically analysed expression patterns in Marchantia gemmae. This allowed us to build a map of precise expression domains and identify a unique set of TFs expressed in the stem-cell zone, providing new insight into the dynamic regulation of the gametophytic meristem and its evolution. In addition, we provide an online database of expression patterns for all promoters in the collection. We expect that the promoter elements characterised here will be useful for cell-type specific expression, synthetic biology applications, and functional genomics.

plant biology↗

bioRxiv2020

Systematic tools for reprogramming plant gene expression in a simple model, Marchantia polymorpha.

We present the OpenPlant toolkit, a set of interlinked resources and techniques to develop Marchantia as testbed for bioengineering in plants. Marchantia is a liverwort, a simple plant with an open form of development that allows direct visualization of gene expression and dynamics of cellular growth in living tissues. We describe new techniques for simple and efficient axenic propagation and maintenance of Marchantia lines with no requirement for glasshouse facilities. Marchantia plants spontaneously produce clonal propagules within a few weeks of regeneration, and lines can be amplified million-fold in a single generation by induction of the sexual phase of growth, crossing and harvesting of progeny spores. The plant has a simple morphology and genome with reduced gene redundancy, and the dominant phase of its life cycle is haploid, making genetic analysis easier. We have built robust Loop assembly vector systems for nuclear and chloroplast transformation and genome editing. These have provided the basis for building and testing a modular library of standardized DNA elements with highly desirable properties. We have screened transcriptomic data to identify a range of candidate genes, extracted putative promoter sequences, and tested them in vivo to identify new constitutive promoter elements. The resources have been combined into a toolkit for plant bioengineering that is accessible for laboratories without access to traditional facilities for plant biology research. The toolkit is being made available under the terms of the OpenMTA and will facilitate the establishment of common standards and the use of this simple plant as testbed for synthetic biology.

synthetic biology↗

bioRxiv2018

Loop Assembly: a simple and open system for recursive fabrication of DNA circuits

High efficiency methods for DNA assembly are based on sequence overlap between fragments or Type IIS restriction endonuclease cleavage and ligation. These have enabled routine assembly of synthetic DNAs of increased size and complexity. However, these techniques require customisation, elaborate vector sets and serial manipulations for the different stages of assembly. We present Loop assembly, based on a recursive approach to DNA fabrication. Alternate use of two Type IIS restriction endonucleases and corresponding vector sets allows efficient and parallel assembly of large DNA circuits. Plasmids containing standard Level 0 parts can be assembled into circuits containing 1, 4, 16 or more genes by looping between the two vector sets. The vectors also contain modular sites for hybrid assembly using sequence overlap methods. Loop assembly provides a simple generalised solution for DNA construction with standardised parts. The cloning system is provided under an OpenMTA license for unrestricted sharing and open access.

synthetic biology↗