Marchantia polymorpha as a new platform for multi-scale modelling and engineering
We have adopted Marchantia polymorpha as a simple model system for plant synthetic biology. We have identified and sequenced a Cambridge isolate of Marchantia polymorpha, and are using the annotated genome to compile a novel library of DNA building blocks based on a common syntax for DNA parts and a technique for rapid assembly of DNA circuits. We are building an open system for reprogramming plant metabolism and form in a simple engineering testbed.
The plants are extraordinarily prolific. A single cross can produce millions of propagules in the form of single-cell spores. Spores can be harvested in huge numbers and stored indefinitely in a cold, desiccated state. Each spore can germinate to produce a new plant, and, unlike higher plants, can undergo the entire developmental sequence to produce an adult plant under direct microscopic observation. Marchantia plants can be easily transformed with fluorescent protein gene markers, and directly visualised using advanced fluorescence microscopy techniques. The early stages of development in Marchantia are open and unobscured by surrounding tissues. This allows easy and direct observation of formative processes during morphogenesis.
Sequencing efforts have provided a draft of the ~280Mbp genome. Most of the major gene families present in more advanced plants are represented by a single or few orthologues in Marchantia, meaning that there is low genetic redundancy. The apparent simplicity of genetic networks in liverworts, combined with the growing set of techniques for genetic manipulation, culture and microscopy, are set to make this primitive plant a major new system for analysis and engineering.
Marchantia polymorpha is the best- studied species of liverwort. Liverworts form a sister clade to modern owering plants, thought to have emerged around 480M years ago.
Male and female plants
Marchantia plants are haploid with a simple prostrate forms. Male (right) and female (left) plants produce distinctive gamete-bearing structures.
Fertilisation results in the production of a short-live diploid phase (sporophyte), which terminates in the production of yellow sporangia.
Millions of spores
Each sporangium contains 100,000’s of spores, which can he stored cryogenically and used for propagation.
Spores germinate rapidly when transferred to suitable media, and the entire process of early development is exposed, and can be visualised directly.
Tiny plants in culture
Germinating spores give rise to plantlets with recognisable body plans and anatomical features within a few days,
Chloroplast development can
be sampled and visualised in a synchronised cohort of germinating spores (image: Bernardo Pollak).
High resolution microscopy techniques allow the non invasive imaging of subcellular features and dynamics in intact plants (image: Fernan Federici).
Marchantia produces oil cells, which are devoted to the production of secondary compounds. The differentiation of these cells can be directly visualised in situ (image: Nuri Purswani).
Cell proliferation, patterning and differentiation results in the formation of repeated air chamber structures across the surface of the plant.
Simple root system
Marchantia lacks a proper root system, instead elongated rhizoid cells perform this role. Speci cation of rhizoids shows similarity to that of root hairs in higher plants.
Marchantia form cup-like organs that spontaneously produce clonal propagules called gemmae.
Gemmae have a regular size and morphology, and can be harvested and germinated for simple observation of engineered growth and development (image: Jim Haseloff)
The dynamics of cellular growth and development can be quantitatively measured and parameterised using quantiative imaging techniques (image: Nuri Purswani).
The Marchantia polymorpha genome is relatively small (280 MB) and comprises 8 autosomes and 1 sex chromosome that make up the haploid genome.
1. A short description of the background and properties of Marchantia as an experimental organism. (Click to download: Intro2Marchantia.pdf, 1.7 MB, 8 pages). See also https://www.openplant.org
2. A review article arguing the need for simple model systems and improved theoretical frameworks to tackle engineering of whole plants. (Click to download: Synthetic Botany, 1.1 MB, 19 pages)