Visualising dynamics in a simple model plant

In Cambridge, we have pioneered the adoption of Marchantia polymorpha as a simple model plant system that is haploid, facile, accessible for direct manipulation and quantitative observation, with simple cellular and genome architectures. We can collect large-scale datasets for single-cell transcriptomes and dynamic expression of cell type specific markers. Marchantia shares the major genetic systems of higher plants. We have tools for systematic genetic modification and will generate CRISPR-mediated knockouts and misregulons for regulatory factors in the genome. Marchantia polymorpha is a model plant system with unique advantages for integrated analysis of genetic interactions and cellular dynamics across the whole organism. Plants produce vegetative propagules spontaneously. Gemma cups provide a ready source of small embryo-like propagules that can be grown and observed at high resolution under the microscope. High throughput automated microscopy can be used to collect datasets from wild type, genetically disrupted and surgically excised and regenerating plants.

  Gemma cup on the dorsal surface of Marchantia polymorpha.  (Image: Jim Haseloff)

Gemma cup on the dorsal surface of Marchantia polymorpha. (Image: Jim Haseloff)

Dissecting regulatory networks

The use of Marchantia allows unparalleled high resolution quantitative observation at the scale of the entire organism, allowing a complete map of cell types and interactions in this simple plant. The genome of Marchantia is highly streamlined, with 398 transcription factors (compared to >2000 in other model plants). Marchantia's complete but reduced set of regulatory elements avoids a major problem with genetic analysis in higher plants, which is complicated by high levels of genetic redundancy. We are constructing a complete set of core promoter elements as standardised DNA parts. These allow construction of markers for genetic interactions, cellular growth, hormonal control, metabolism and source-sink relationships in the plant.

  Plant transcription factors . Image: http://planttfdb.cbi.pku.edu.cn (above)  Plant transformation vector . Image: Bernardo Pollak (right)

Plant transcription factors. Image: http://planttfdb.cbi.pku.edu.cn (above)
Plant transformation vector. Image: Bernardo Pollak (right)

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Promoter elements can be used to create multi-gene DNA constructions, and transformed into Marchantia. As transformants regenerate, the plants spontaneously produce gemma as a part of normal growth. Gemma provide a simple and accessible form of the organism to observe processes of growth at widely different scales - from subcellular dynamics to cellular interactions to whole organism morphogenesis.

  Marchantia gemma, showing direct visualisation of gene expression through multiple nuclear-localised fluorescent protein gene fusions . (Images: Bernardo Pollak & Mihails Delmans)

Marchantia gemma, showing direct visualisation of gene expression through multiple nuclear-localised fluorescent protein gene fusions. (Images: Bernardo Pollak & Mihails Delmans)