In November of 1956, after weeks of protests and calls for free elections in Hungary, Soviet tanks rolled into Budapest to crush the uprising. Well over a hundred thousand people fled the country seeking asylum. Among them was a young geneticist named George Rédei, who headed for the Austrian border with a small vial of seeds tucked in his pocket.

The seeds belonged to a spindly weed in the mustard family called Arabidopsis thaliana. Today, that weed is widely regarded as a botanical superstar. Arabidopsis has been the focus of some 100,000 research papers. Its seeds have flown around the Moon; it is the go-to plant for experiments on the International Space Station. And when the scientific community decided which plant should be the first to have its genome sequenced, Arabidopsis emerged as the winner. This year marks the 25th anniversary of when the world got its first glimpse at that genome, launching the much-studied plant toward even greater fame and scientific value.

Setting off from his homeland, Rédei could never have predicted all the ways that Arabidopsis would revolutionise understanding of plant biology, from root to shoot. Discoveries made in the little weed laid the groundwork for ways to improve crops and enhance food security, to manage ecosystems and mitigate climate change. The plant even yielded insights into animal evolution and human health. The Arabidopsis genome still serves as the first reference for researchers investigating genetic and development puzzles in other plants.

But the plant’s fame was never a given. It took years for Arabidopsis to prove its mettle against money-making crops like corn. Early on, funding was uncertain. It was Rédei and then a small but ambitious community of young scientists who took up the Arabidopsis campaign and brought the little plant into the limelight. The world of plant biology — and all of science — hasn’t been the same since.

Secrets of plants and beyond

After fleeing Hungary as a refugee, Rédei eventually made it to the University of Missouri in Columbia in 1957. On the faculty there, he planted the Arabidopsis seeds he’d brought across the ocean. He was familiar with the work of German botanist Friedrich Laibach, who had realised that the weed could be a powerful biological research tool, a model organism akin to the fruit fly Drosophila melanogaster. Rédei became convinced of the plant’s prowess; he hoped that it could help reveal the genetic secrets of all plants and perhaps other living things.

He was an outlier. At the time, most plant research focused on farm crops or decorative plants – plants with obvious economic value. Scientists usually studied their favourite species to answer specific questions: To figure something out about fruit ripening in tomatoes, you did experiments with tomatoes; to understand flowering time in cotton, you turned to cotton.

Scientists had already made some profound discoveries – with broad implications – by studying plants. Gregor Mendel’s famous work on garden peas in the mid-1800s led him to uncover the basic principles of how traits are inherited (though the implications of his experiments weren’t appreciated until the early 1900s).

Corn too, was an early model for investigating genetics. In one fascinating example in the 1940s, geneticist Barbara McClintock was tracking mutant corn plants with strangely coloured kernels. She would ultimately show that these oddballs often resulted when bits of chromosomes were deleted or broken – sometimes genetic material was even transferred from one chromosome to another. The discovery of these “jumping genes”  which were later found in all kinds of species, including people – led, decades later, to her 1983 Nobel prize.

Mutant organisms, like McClintock’s corn plants, were a crucial tool in the early years of genetic research. Identifying how a particular gene affected an organism typically involved looking at what happened to an organism when the gene didn’t work. You began by seeking mutant versions of the organism (say, a fruit fly with white eyes instead of red) or you created mutants — with plants this meant zapping the seeds with X-rays or chemicals. When you grew those seeds, one among thousands of the infant plants might be weird. Maybe it couldn’t bend its stem toward the light, or its leaves lacked green pigment.

You then worked backward from the mutant to try to figure out what gene or genes had been disrupted. But that was far from easy. It often took generations of genetic breeding and years of careful experiments to identify the precise gene involved, let alone understand what that gene did.

And doing those investigations in a plant such as corn carried extra challenges. It required acres of fields, farm machinery and lots of patience. In breeding experiments set up to discover the effects of a gene, or how a trait changes over generations, you had to wait through a months-long growing season for seeds to mature. Then you had to wait until the next spring to plant those seeds. Then you had to wait for those plants to grow their own offspring. Greenhouses and colleagues living in warmer places with longer growing seasons could help, but the timeline was always long.

Rédei thought that Arabidopsis could circumvent those problems, and other challenges besides. Laibach, in Germany, had already detailed many of the qualities that made the plant so amenable to genetic studies — its small size (thousands could be grown in a small room); its short generation time (six weeks); its prolific seeds (more than 10,000 per plant). Laibach’s observations with a microscope had also revealed that Arabidopsis has only five pairs of chromosomes — whereas corn has 10 pairs, and wheat has 21. That would make it much simpler to map a particular gene to a particular spot on a chromosome.

In Missouri, Rédei continued to investigate the little mustard, conducting experiments with Arabidopsis plants grown from seeds he’d procured from Laibach before leaving Hungary. A small community of researchers, mostly in Europe, were also working with the plant, but there was little outside interest – indeed, after initially funding Rédei’s research, the US National Science Foundation withdrew its support in 1969. It reasoned that a plant – a weed, no less – would never generate useful knowledge.

A promising plant for the molecular era

Still, Rédei kept at it and in 1975, in the Annual Review of Genetics, he argued the plant’s case to the broader scientific community.

Not long after, Chris Somerville, fresh off a PhD in E. coli genetics, and his wife, plant pathologist Shauna Somerville, read Rédei’s paper and decided that Arabidopsis was the right organism to usher plant science into the modern, molecular era. Scientists working with the E. coli bacterium had recently developed ways to cut strands of DNA and fuse them back together; by 1978, researchers using those techniques had engineered the bacterium to make human insulin. Scientists like the Somervilles – many of whom had begun their careers studying other long-standing model organisms, such as yeast, bacteria and fruit flies – began eyeing Arabidopsis as a promising tool for probing life’s mysteries at the molecular level.

“It was very attractive for people who were working on other systems and had a bit of a pioneering spirit to try something new,” says biologist Elliot Meyerowitz of Caltech. Meyerowitz had recently finished a PhD focused on Drosophila developmental genetics and had also read Rédei’s review paper. When he started his own lab at Caltech, its main focus was Drosophila development and genetics, but pretty soon it was investigating Arabidopsis too.

Over in the Netherlands, plant scientist Maarten Koornneef was working on a genetic map of Arabidopsis – a guide to where the plant’s various genes were located on its chromosomes – using data garnered in part from Rédei’s work and Koornneef’s own investigations of all sorts of mutant plants. Such maps could help scientists find a particular gene – say, one that prompted early flowering, larger seeds or resistance to a fungus – clone that gene, and then look for it in other plants.

Meanwhile, at the University of Illinois, the Somervilles were investigating how plants regulate their use of carbon dioxide with Arabidopsis mutants that couldn’t grow in regular air, but could grow in air enriched with carbon dioxide. This research laid the groundwork for ways to make photosynthesis more efficient in various crops and led to some high-profile papers that brought the plant to the attention of still more scientists. When the duo moved to the Department of Energy’s plant research laboratory at Michigan State University in 1982, they began several other Arabidopsis projects – and they attracted new converts.

Among them was Mark Estelle, who had just finished a Drosophila-focused PhD. At first, Estelle tackled oats – an important plant, but one with a large, complex genome. “That didn’t last very long, because that’s a ridiculous genetic system,” he says. A model organism, though, would allow for sophisticated genetic experiments that then could be applied back to plants of economic importance. He made the switch to Arabidopsis and began investigating auxins, a class of potent hormones that coordinate growth and development in plants.

“We could screen a thousand plants in each Petri dish looking for mutants,” says Estelle, who continues to use the little plant to investigate auxins at UC San Diego. “That’s very powerful.”

Meyerowitz’s lab then made a compelling discovery. Experiments led by Leslie Leutwiler, a post-doc in his lab, had found that the Arabidopsis genome was on the small side. Their estimates suggested it had a mere 70,000 kilobases pairs (kbp) of DNA — in contrast with estimates of 1.8 million kbp for soybeans and a whopping 5.9 million kbp for wheat. And those five pairs of Arabidopsis chromosomes didn’t have huge quantities of DNA sequences that were duplicated over and over, like some plants did. This made it much more technically feasible to hunt for genes in a haystack of DNA, as Meyerowitz and his graduate student Robert Pruitt pointed out in in the journal Science in 1985.

And the results kept coming. In 1986, plant molecular geneticist Caren Chang, then a graduate student in Meyerowitz’s lab, cloned and sequenced an Arabidopsis gene for the first time; it carried instructions for making an enzyme that helps plant cells survive when they are starved of oxygen — for example, during times of flooding. “So little was known then,” Chang, now at the University of Maryland, says of those salad days. “It was this big open frontier.”

That same year, another beneficial characteristic of Arabidopsis was added to list: The plant could easily and efficiently take up foreign genes with the help of a DNA-carrying bacterium, a process known as genetic transformation. Scientists had been racing to insert new genes into plants since the late 1970s. It was a team of Monsanto researchers who put all the pieces together in Arabidopsis, showing in a 1986 Science paper that they had put an antibiotic-resistance gene into the plant.

Things were coming to a head. Despite earlier pushback — many crop scientists at the US Department of Agriculture had considered Arabidopsis an annoying upstart and were rumoured to refer to it as “the A-word” — the larger scientific community knew that it needed a model plant if the field were to progress.

“One of the reasons why we needed a model, why every field needs a model, is because the development of new techniques, especially molecular biology techniques — it’s complex. It’s expensive, it’s time consuming,” says molecular biologist Marc Somssich, now at the seed company KWS Saat in Germany, who wasn’t involved in those early days but chronicled them in a 2019 paper. “So instead of developing new techniques for a thousand different plants, we develop these techniques for one.” A model plant would mean standardized techniques, shared lab protocols, organism-focused conferences — and everyone benefiting from the greater accumulation of knowledge.

Tomato was under consideration; so was petunia. But Arabidopsis pulled into the lead. Discoveries made with the little mustard kept appearing in high-profile science publications. A critical mass of scientists, including heavyweights like James Watson, co-discoverer of the structure of DNA, and yeast geneticist Gerald Fink took up the Arabidopsis banner.

At the National Science Foundation, new leadership, including plant biologist Mary Clutter, understood the value of bringing the plant community into the modern era. In 1990, the NSF developed a coordinated international strategy of Arabidopsis research goals. This included an ambitious plan to sequence all the DNA letters in its genome.

“Think of Arabidopsis as the Hyundai of plants,” Fink told Mosaic, the NSF’s flagship magazine, in 1991. “If the Hyundai represents ‘car’ at its most fundamental, Arabidopsis is the essence, the stripped-down version, of [a] flowering plant. What we learn from it will most certainly be applicable to any plant of agricultural importance. It will tell us a considerable amount about how all green plants are structured and ultimately, perhaps, how their genomes may be modified to enhance productivity.”

In December 2000, the Arabidopsis Genome Initiative, which involved scientists from around the world, published the sequence of the Arabidopsis genome in Nature. The genome provided a draft recipe book for plant life. It revealed some 25,000 genes (a later, more accurate count put the number of genes at over 27,000), roughly 30 percent of them with completely unknown functions. It provided fodder for countless hypotheses and experiments that were to come.

A blooming of discoveries

It is impossible to do justice to the discoveries made in the plant since – and to the contributions that each member of the dedicated Arabidopsis research community has made to science.

Since Charles Darwin, for example, scientists had been probing how plants detect blue light, which prompts them to bend toward the Sun. In the 1980s, researchers bred mutant Arabidopsis plants that didn’t respond normally to the blue light signal. Pinpointing the defective gene in the plants soon revealed the first blue-light detector, called a cryptochrome.

Cryptochromes and other light sensors turn out to be critical for how plants integrate an external cue — light — with internal molecular clocks that regulate growth and development, germination time, flowering time and more. And cryptochromes have since been found across the tree of life: in fruit flies, algae, fungi and mice; they are also key in people. Cryptochromes sense the light that sets the body’s circadian rhythms — off-kilter rhythms can contribute to ills such as cancer, heart disease and depression.

Arabidopsis also lent a hand to researchers investigating how flowers and fruits develop their particular shapes and sizes. Among the mutants catalogued in the early days were plants that had one organ replaced by another — they had petals where stamens should grow, for example. Animal versions of these mutants had been investigated in flies (they were tiny monsters with, for example, a leg growing where an antenna should) and research using Arabidopsis revealed the floral version of such body plan genes. This work continues to aid scientists probing the stunning diversity of floral forms, including the abundant petals in “double flower” roses and the lack of sepals in tulips.

Related work on molecules involved in controlling fruit size may one day lead to larger fruits, including kiwis and cucumbers. These regulating genes are also shedding light on how plants we eat today have changed over the eons: In 2015, for example, scientists discovered that a naturally occurring mutation in one of these genes gave rise to the gigantic, fat fruits known as beefsteak tomatoes.

Arabidopsis has also shed light on how plants cope with stresses in their environment. A key plant biochemical signalling pathway was discovered in Arabidopsis and later identified in crop plants, including rice and tomatoes. It dealt with responses to an overload of salt, which makes it harder for roots to take in water and hinders growth.

How plants respond to additional foes – bacteria that slip in through plant pores or wounds, insects that stab into a leaf, fungi that slither among plant cells – also came under scrutiny in Arabidopsis, and some of the discoveries had repercussions far beyond the plant world. Unlike mammals, plants don’t have roving immune cells that keep an eye out for pathogens (and keep track of past encounters). Instead, each plant cell must rely on its sturdy cell wall, its own detection machinery, and signals sent plant-wide from the site of the infection or attack.

In 1994 and 1995, scientists reported the discovery of genes that code for a class of plant proteins called NB-LRR receptors, which are critical to the plant immune system. After the Arabidopsis genome was sequenced, investigations of these genes accelerated — Arabidopsis has nearly 150 of them. It turns out that versions of NB-LRR receptors play a role in the inflammatory response of mammals, including people. Variations in some of the NB-LRR genes have been implicated in Crohn’s disease.

Despite the fact that animals and plants went their separate evolutionary ways about 1.6 billion years ago, many human genes known to play a role in disease have related versions in Arabidopsis. That includes some 70 percent of human genes implicated in cancer, a count that is higher than for either yeast or Drosophila. Genes implicated in neurological disorders, including Alzheimer’s and Parkinson’s, also have versions in Arabidopsis.

The plant also laid a foundation for many biotechnology techniques used in labs today. Methods developed to investigate gene activity in Arabidopsis cells, for example, were adopted for use in zebra fish, Drosophila and even studies of the optic nerve in frogs. The Arabidopsis cryptochromes are harnessed for studies of mammalian cells that employ optogenetics, a method that allows scientists to investigate and control nerves and other cells using pulses of light.

The list goes on and on, with new findings about the plant continuing to roll out. But will it maintain its status as preeminent model of the plant world? Yes and no. For one thing, molecular biology techniques have become faster and cheaper: While sequencing the Arabidopsis genome took a decade and cost nearly $75 million, today a genome can be sequenced in a day for about $600. This makes it much easier to investigate any plant.

Still, it’s unlikely that any single plant will take Arabidopsis’s place. The community that grew around the little weed, with its commitment to sharing resources, data and lab protocols, can’t be underestimated, and it’s still going strong, says molecular biologist Anna Stepanova of North Carolina State University, who is on the board of directors for the Multinational Arabidopsis Steering Committee. “I’m very optimistic about Arabidopsis staying relevant for hundreds of years to come.”

While enthusiasm for Arabidopsis hasn’t changed, the world of science has — change that the mustard helped foment. Scientists no longer labor in discrete and often siloed disciplines, focusing on physiology or on biochemistry or on morphology or genetics, as they did when Rédei was coming up. The molecular revolution shook up everything, connecting these disciplines and fusing genetics with physiology, development, pathology and more. This integration was already happening among researchers studying other models like E. coli and yeast. Arabidopsis brought it about in the plant world.

A great many of “the classical questions that had been raised by earlier botanists are answered in a molecular and mechanistic level by research on Arabidopsis,” says Meyerowitz. “And a lot of new questions were opened up from that research that people may not even have considered before.”

There are still many such questions, says Chris Somerville. And the weed still has a place in answering them.

“It’s a wonderful place for people to learn about the basic process,” he says. “So first you go to Arabidopsis and you say, well, how is Arabidopsis doing this aspect of biology? And then you can translate it now into the other plants — the other plants we care about.”

Rachel Ehrenberg is an editor at Knowable Magazine.

This article was first published on Knowable Magazine.