Scientists Discover a New Plant Organ

The structure, called a cantil, holds up the flower-bearing arm of the thale cress, a long-studied species

Thale cress
On the center plant, poking out from the stem is a bent side stalk, which holds up the arm of the plant with a flower. Tim Gookin

The thale cress may be a humble weed, but to science, it’s an important model organism. Researchers use the plant as a proxy in experiments to represent other plants, animals and even humans—thanks to its relatively short lifecycle and simple genome. Scientists have even sent the thale cress to the International Space Station and the moon.

“It’s the fruit fly of the plant world,” says Tim Gookin, a molecular biologist who formerly worked at the Pennsylvania State University.

But despite the fact that scientists have scrutinized the plant, Aribidopsis thalania, since the 16th century, the thale cress still manages to surprise. Gookin and his team have found that the thale cress produces a previously unreported plant organ, as described today in Development.

This wonky-looking plant part is similar to the cantilever beams that buttress the underside of bridges, and is called the “cantil.” The newly discovered part juts out from the stem and connects to the flower-bearing arm of the plant, which is known as the pedicel. Thale cress cantils give the plant the appearance of bent elbows; cantil-less plants seem to have only straight arms. Cantils are neither part of the stem nor the pedicel. They’re an entirely new organ, says Gookin.

How did scientists miss an entire plant body part all this while?

One reason, Gookin concluded, is that cantils only form when the thale cress delays its flowering, usually during spring when daylight is limited. In this season, the thale cress transitions more slowly from the leaf-production phase to the reproductive flowering stage, compared to during the sunshine-filled summer. At this decelerated pace, the cantil slowly manifests at the cusp of flowering, right after the flower-tipped pedicel makes its debut. If the plant only experiences seasons with long hours of sunshine, the cantil will never make an appearance. Researchers often grow the thale cress under long-daylight conditions so as to accelerate to the seed-production stage, not giving time for the cantil to develop.

Another reason for the cantil’s obscurity is labs’ widespread use of a thale cress mutant strain that doesn’t produce the buttressing structure. This Ler strain bears a mutation in a gene that Gookin says prevents the plant from producing the part.

“If you base all of your research on this type of plant, you will never see [the cantil], because it's automatically cancelled for you,” says Gookin.

Gookin’s discovery that the cantil is a new organ comes after a painstaking twelve-year investigation. When he first observed cantils in thale cresses in 2008, he fretted that the part had arisen after he had mixed up his seeds or after different strains had cross-fertilized in the lab. After several years of growing natural strains of Arabidopsis, he finally confirmed that cantil formation is a naturally occurring phenomenon. Then came the arduous investigation of identifying why natural Arabidopsis strains only bear cantils on occasion. Gookin ruled out the effects of the soil, water, fertilizer and air supply. Eventually, he found that if he genetically tweaked the plants to delay their floral production, they would eventually bear crooked side stalks—cementing the role of flowering delays as the culprit behind cantils. For his discovery of the cantil’s origins, he says that he hand-raised 3,782 plants and inspected over 20,000 pedicels.

Gookin’s hard-won findings may be the gateway to understanding cantil growth in other plants, says Daisuke Urano, a botanist at Temasek Life Sciences Laboratory, Singapore who wasn’t involved in the study. Cantils have yet to be documented in any other plants, but Urano says that cantils or similar structures probably exist in other shrubs.

Cantil formation can help us understand how plant structures are formed in general, says Nicholas Provart, a systems biologist at the University of Toronto who wasn’t involved in the study. Provart says this could be important for developing more productive plants strains in agriculture. As an example of how optimizing plant structure can boost agricultural productivity, he points out that scientists cultivated shorter variants of wheat and rice strains in the 2000s that led to higher agricultural yields, as dwarfed plants are less floppy and more stable. “There are definite benefits,” says Provart, “just by changing the architecture of plants in certain ways.”

While it’s unclear now how the cantil itself may have any direct agricultural importance just yet, “it's also just useful from a scientific perspective,” says Provart. “Sometimes things get discovered and then, 10 years down the road, or 15 years down the road, someone picks up on it … That's a little bit how science works—it's this collection of seemingly random discoveries.”

Provart estimates that there are roughly 78,000 papers published that involve the thale cress, “so it's kind of funny to see some new parts being described after all of this research has been done on Arabidopsis,” he says.

Arabidopsis has been in the scientific area for years—decades,” notes Urano. “Everyone uses Arabidopsis, probably more than 10,000 researchers in the world.” He adds, “Still, scientists find a new organ … That's amazing.”