Plant Model Species: Who, What & Why?

Plant life: Model plant species: Who, what, and why?

Every sub-section of biology has a model species that every biologist loves (or loathes). A model species is a well characterised and easy to grow organism, often with a fully sequenced genome. This makes it way easier for biologists to understand, investigate, and uncover new information and translate. Once this new finding is discovered in one model species, more often than not, it’s also found in a close evolutionary partner. This then gives us insights into how a particular pathway, mechanism, or response is conserved across species, or even entirely different biological kingdoms. Model organisms are also chosen based on behavioural similarity. You may think human beings are a cut above the rest, but you’d be surprised how similar we are to our ‘distant’ cousins.

Mammalian genetics mostly revolves around two very unassuming heavyweights: the fruit fly and the zebra fish (AKA Drosophila melanogaster and Danio rerio) (and no, the second isn’t a Game of Thrones character). The fruit fly has a tiny genome, which means nearly every biological function is mapped, and characterised. Fruit flies are especially well suited to developmental biology: how an organism grows, from fertilisation through to a fully differentiated and functional fruit fly.

model organisms
A fruit fly (Drosophila melonogaster) and a zebra fish (Danio rerio), common model organisms used in developmental human genetics

What about zebra fish? They first made mainstream news headlines in 2003, when glow in the dark fish were introduced to US markets, based on the work of Singaporean scientist, Dr. Zhiyuan Gong. Initially, these fluorescing fishes were developed as a toxicity sensor for polluted rivers in the fish’s native India. But, the ingenious sensor was capitalised on, and you can now buy GloFish® in aquariums up and down the US.

Danio GloFish, harbouring a gene isolated from a jellyfish

Moving on from fish and flies, it’s time to look at plant science’s big guns: a weed, and a highly regulated addictive substance.

Arabidopsis thaliana (ara-bid-op-sis tha-lee-an-a) is commonly known as Thale cress. It’s a small, radial plant, with leaves growing flat to the ground, shooting flowers near vertically up. It can grow nearly anywhere, in a variety of harsh conditions. It’s also a global plant, so different accessions (the same species identified from a different location) allow plant scientists to unpick what makes these plants tick under a variety of different stressors.

Arabidopsis is dicotyledenous, meaning when it first germinates from a seed, two tiny ‘leaflets’ (not the kind the takeaway puts through the door) are produced. From there, two ‘true leaves’ are formed, and the plant continues to grow. Underground, a taproot system forms: think of a carrot. There’s a main root, with a series of lateral roots, which forage for nutrients and water in the soil, to ensure a healthy, happy plant. Arabidopsis plants grow fast, are hardy, and can be made to harbour specific genes of interest (yes, this includes glow in the dark proteins!)

So, what about this addictive substance? It’s tobacco! Most labs use either Nicotiana benthamiana or tabacum. Benth is standard tobacco’s smaller, more flimsy cousin, but both are frequently used in plant labs all over the world. So, why use tobacco? It’s no secret, for corporate tobacco companies, it made a lot of sense to get their best selling product sequenced. Before this, loads of information had already been accrued, given its importance socially, historically, and economically.

Model plant species
A: Arabidopsis thaliana (Thale cress) B: Nicotiana tabacum (Tobacco). 

Tobacco can be used as a model for crop species, as it’s more closely related to barley, wheat, and rice. N. benth is also used for virology studies; helping plant scientists understand the diseases that kill off our food supplies every year. Unlike Arabidopsis, tobacco has a fibrous network of roots.  It’s also useful for ‘transient’ studies, a gene or fluorescent tag can be introduced to quickly check that your experiment is going smoothly, before you ‘stably’ transform Arabidopsis. The downside to tobacco is it’s huge, in size and genome. This makes it much harder to ‘genetically’ navigate and characterise. To stably transform tobacco, it’s not nearly as easy as its weedy counterpart, it needs to be morphed back into a stem-cell-like blob (called a callous), before turning back into a fully functional tobacco plant. Cool, right?

This is just the tip of the botanical iceberg, as we all know. Check back soon for more insights into the weird world of plant science.

Interested in knowing more? Tweet me @emilyxarmstrong, or comment on this post.



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