Unremarkable Weed to Remarkable Model Organism: Arabidopsis thaliana

Briefly
Arabidopsis thaliana is a small weed with no particular importance either agriculturally or economically. However, it was the first plant to have its entire genome sequenced and is the dominant model organism used in plant biology. Over the course of 70 years (1930-2000) a few key scientists saw the potential of A. thaliana as a model organism and despite the large resistance and scepticism, eventually saw it established and widely used. Coinciding with key developments in modern molecular biology techniques and the collaboration of dedicated researchers, Arabidopsis thaliana went from an ignored and irrelevant weed to an invaluable research tool for molecular biologists and geneticists and was largely responsible for increasing plant molecular biology as a field. 

In Depth 
Arabidopsis thaliana (also known as thale, mouse-ear, and rock cress), considered a weed, is a small and unremarkable flowing plant with no agricultural importance. However, despite this apparent lack of interesting characteristics, Arabidopsis thaliana (Arabidopsis from here on) is the main model organism used in plant biology with more research resources allocated to it than other memorable model organisms, such as the mouse and fruit fly [1]. What it lacks in physical charm, it more than makes up for in its usefulness to plant scientists. 
Arabidopsis is the organism that I work on and I have found that whilst people remember fruit flies and white mice as model organisms from science lessons at school, Arabidopsis seems comparatively less well known outside of plant science. Therefore, I thought that I would do a small appreciation post on the remarkable journey from weed to model organism. I am going to attempt to cover a rather long story quite succinctly whilst also giving a bit of information on its natural history and key characteristics/facts. But I will reference and link articles that go in depth on each specific area. 

Natural History and Favourable Characteristics 
Arabidopsis thaliana belongs to the family of flowering plants known as Brassicaceae, which includes notable crops such as rapeseed, mustard, cauliflower and several cabbages [2]. However, despite the agricultural importance of its relatives, Arabidopsis is a small (reaching around 10cm), widely distributed weed with no agronomic importance. Originally native to Western Eurasia, Arabidopsis thaliana has extended its distribution to cover a large range on the planet and is now also found in North America and East Asia [2]. Due to the wide-spread distribution, it experiences and adapts to a variety of climates, differing from its close relatives many of which are endemic to specific areas and have not colonised warmer regions. Arabidopsis thaliana is adept at colonising habitats that are poorly suited to other plants, surviving and thriving in rocky, low-nutrient, stony soils but can also be found in forests and grassy, meadow habitats [2,3]. Many of the biological attributes of Arabidopsis thaliana play a large role in its modern uses. ​

Adult Arabidopsis thaliana plant

For example, it has a rapid life cycle of between 6 and 8 weeks, this quick growth makes multiple replicates of experiments much easier to conduct. Additionally, the aforementioned small size allows them to be grown without taking up excessive amounts space. Furthermore, Arabidopsis can reproduce through self-fertilisation (or selfing) making it particularly easy to breed and cross different lines. It forms a fairly compact rosette stage and produces a comparatively large number of small seeds (another advantageous trait for research). The evolution of several, of what became key, characteristics set Arabidopsis thaliana apart from its close relatives, including other species within the genus Arabidopsis. ​

History and Road to Fame 
Arabidopsis thaliana has come a long way since its original discovery in the German Harz mountains by Johannes Thal in the 16th century and original name Pilosella siliqousa. Much of its widespread use and fame begins with the work of Friedrich Laibach, a German botanist [4]. Prior to Laibach's interest, in his words, "Arabidopsis was only known to florists and taxonomists, who had nothing better to do than constantly change its name and systematic positioning" [4]. Laibach became interested in this small plant predominantly due to the large variety observed in its phenotype, which lead him to meticulously collect seeds from different Arabidopsis populations from every location that he visited [1,4]. Interestingly his seed collections were the base from which the Arabidopsis Information service (AIS) seed bank was built from in the 1960s. The AIS in turn was the foundation from which the Columbus (ABRC) and Nottingham (NASC) seed stock centres would be formed from many years in the future (both of which I use as part of my research). 
Laibach went on to determine that Arabidopsis contains five chromosomes, a relatively small number and publish a paper in 1943 proposing that it would make for a good model organism. He supported this proposal with the facts that Arabidopsis is easy to grow, contains a small genome, has a short life cycle, produces a large quantity of seed and can be easily crossed, all characteristics which make for a good model organism. However, this idea was largely ignored and would be for 40 years. 
Some, however, saw the logic in Laibach's proposal and the potential in Arabidopsis. One such researcher was George Redei, a Hungarian biologist. He started his own laboratory in Missouri and obtained 4 Arabidopsis lines from Laibach to conduct work on. For 20 years Redei was the only scientist working on Arabidopsis in America, something that made acquiring funding particularly difficult. As part of his research, in 1957 Redei exposed Arabidopsis seeds to x-rays and screened for interesting mutants, this led to the discovery of a mutant line with stunted growth which came to be called Arabidopsis erecta. This line became one of the most frequently used for molecular and genetic studies. 
Over the course of the next 20 years the amount of research and interest in Arabidopsis slowly grew and a small community of dedicated researchers began to form. 1965 saw the first International Arabidopsis Symposium, held in Germany, and hosted 25 scientists [4]. Following the traction Arabidopsis research was gaining, Redei followed Laibach's example and published a paper in 1975. With the title 'Arabidopsis as a genetic tool' Redei reiterated the many points originally detailed by Laibach that point towards the use of Arabidopsis and its worth as a model organism [4]. This paper further added to the interest and after its publication several influential papers were published, and Arabidopsis became more solidified as a model organism. 

It was in the 1980s however when Arabidopsis research really hit its stride. Yet another article, presenting the same points as Laibach and Redei, was published pushing the narrative of Arabidopsis as a model organism but this time it found its way into the prestigious Science journal. During this time, modern molecular biology was developing rapidly with new techniques being developed. Crucially, the cauliflower mosaic virus 35S promoter was discovered and this led to the first transgenic Arabidopsis plant being produced through agrobacterium mediated transfer. I won't go into detail on this technique (perhaps the topic for a future article) but transgenically engineering plants using Agrobacterium is a fundamental technique in plant molecular biology. 

A rosette stage Arabidopsis

This was a huge win for plant molecular biology and the ability to be transformed was another useful attribute that could be added to Arabidopsis' already long list. This was a particularly important moment as a contributing factor behind the original slow growth in Arabidopsis research was its resistance to mutations.  
​Following on from these key moments Arabidopsis has been the dominant model organism in plant molecular biology. Whilst a lot of the original research was conducted on the Arabidopsis erecta line described by Redei, the Columbia line was chosen to have its genome sequenced. This was in no small part due to the fact that A. erecta was a mutated line as a result of the x-ray experiments. The Arabidopsis Genome Initiative (AGI) set out and accomplished their aim to sequence the full genome of the Columbia line of Arabidopsis and it became the first plant with this accolade in the year 2000. This finally solidified Arabidopsis as a model organism in plant biology. This Columbia line is widely used today, and I have a large number of tubes labelled Col-0 (referring to seeds of this line). ​

To finish off 
The road from ignored, unremarkable weed to a dominant model organism was a long and slow one for Arabidopsis. Something I enjoyed learning about during my research for this article was the importance of a small but strong community of scientists who "exhibited an admiral level of collegiality and cooperation" [5]. The development of shared resources and strong collaboration between researchers was key in establishing Arabidopsis as a model organism. You often hear of scientific discoveries involving a high level of competitiveness with different research groups racing to beat others to the findings. Whilst this competition has certainly played a big role in pushing scientific research forward, it was interesting to read a story in which collaboration and shared knowledge played such a large role. 
I have attempted to cover this long and multifaceted journey relatively succinctly and therefore was forced to leave out many details. I have included key moments and the parts that I found particularly interesting. The research has certainly spawned ideas for future articles but if people are interested in the story of Arabidopsis and want more depth then I recommend checking out the articles that I have referenced. I hope you enjoyed this article, despite its dominance in the world of plant science, the vast majority of people have never heard of Arabidopsis and are unaware of the part it has played in important research. Hopefully, I have brought the story of this unremarkable yet remarkable weed to more people. 

As always, I welcome any feedback and don't forget to find me on social media: 
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References 
[1] Leonelli, S. (2007). Arabidopsis, the botanical Drosophila: from mouse cress to model organism. Endeavour, 31(1), 34-38. 
[2] Kramer, U. (2015). The natural history of model organisms: Planting molecular functions in an ecological context with Arabidopsis thaliana. eLife, 2015(4). 
[3] Mitchell-Olds, T. and Schmitt, J. (2006). Genetic mechanisms and evolutionary significance of natural variation in Arabidopsis. Nature, 22(441), 947-52. 
[4] Somssich, M. (2019). A short history of Arabidopsis thaliana (L.) Heynh. Columbia-0. PeerJ Preprints, 7. 
[5] Koornneef, M. and Meinke, D. (2010). The development of Arabidopsis as a model plant. The Plant Journal, 61, 909-21.