Arabidopsis thaliana, the lab rat of plants

Plant scientists are obsessed with a little weed called Arabidopsis.

On the surface it’s a strange plant to study; it’s not grown for food nor to feed animals, it’s not ecologically important and its flowers are, frankly, boring. Yet tens of thousands of researchers around the world dedicate their careers to discovering everything there is to know about thale cress, Arabidopsis thaliana.

This little weed is more than it seems. Like rats, E. coli and fruit flies, Arabidopsis is a model organism. Scientists study model organisms to learn their basic biology, which can be extrapolated into other related species. Arabidopsis can tell us a lot about crop plants, many of which are notoriously difficult to study. It’s even given us an insight into human diseases!

What makes Arabidopsis a good model plant?

Arabidopsis is a weed, which is great for research because it’ll pretty much grow anywhere, from soil to Petri dishes to liquid nutrient solutions. The mature plants are only about 5-10cm in diameter, so you can grow hundreds of them in a typical growth chamber. Best of all, it’s fast growing, going from seed to (irritatingly small) seed in just 6 weeks.

Arabidopsis seeds are tiny!

What really separates Arabidopsis from the crowd is its tiny genome. It has around 27,500 genes encoded within a genome of 125 million bases (letters) of DNA. Contrast this with the huge genomes of crop plants like barley (30,000 genes, 5.1 billion bases) and wheat (96,000 genes, 17.1 billion bases) and it’s easy to understand how Arabidopsis was the first plant to have its genome sequenced, way back in 2000 (a year before the Human Genome Project was completed). Since then, fantastic genetic resources have been developed in Arabidopsis, leading to a revolution in plant science.

Arabidopsis’ impact

By deciding to focus on Arabidopsis, scientists around the world were able to share knowledge and rapidly build upon new ideas. Many people, including myself, believe that this had led to a much broader and deeper understanding of plant biology than we could ever have achieved otherwise.

One way to understand the function of a gene is to stop it from working properly and look at the effect on the plant. The Arabidopsis genome sequence has allowed scientists to develop huge libraries of “mutants”, plants deficient in every single known gene. We knew the basic processes of plants from work done on crops over 100 years ago, but didn’t really understand the details. By working backwards from the mutants, we are able to discover which genes are responsible.

Genes from different species have some changes. The less closely related they are, the more different they are likely to be. Image produced in ApE.

The next stage is to translate the knowledge gained in weedy little Arabidopsis into more useful plants, like crop plants. Even though they look so different, almost all the genes you find in Arabidopsis are present in all flowering plants.

Barley in a growth cabinet

Using the new genome sequences of plants like wheat and barley, it’s easy to search for Arabidopsis genes in these crops. It’s a bit like Google. Stick the letters in and it’ll give you the best matches. Different plants usually have a few changes in the sequence of a gene, but the best match is usually the gene you’re looking for.

From there it’s a matter of silencing the gene you have identified in your chosen crop plant to see if it has the same impact as it did in Arabidopsis. If so, you’ve just improved our understanding of an economically important crop species.

The future of Arabidopsis

Genome sequencing is becoming increasingly cheap and easy. Will we still need Arabidopsis in a world of species-specific genomes? I’d argue yes, at least for a decade or two yet. It is still comparatively very difficult to work with crop plants directly. We don’t yet have full libraries of mutants so Arabidopsis plays a vital first step in gene identification. A full understanding of genes in the model plant would make it a lot more easy to investigate their functions in crop species. Future research areas like synthetic plant biology are predicted to be developed in Arabidopsis too.

Arabidopsis thaliana is the backbone of plant science. Its genetic resources have led to great leaps in our understanding of plant biology, focussing research and enabling translation into crop plants.

Weeds are flowers too, once you get to know them – A. A. Milne