Plants don’t have bones or muscles or brains, but they’re always on the move. Driven by their genetics, some are hardwired to flower in a freeze. Others figuratively hold their breath to survive floods. Still, many of us know others die if you look at them funny.
Like Charles Darwin, botanist Simon Gilroy is obsessed with the mysterious behaviors of plants. Darwin, the “father of evolution,” spent decades meticulously observing plant movement, from vines that can circumnavigate almost anything to carnivorous plants that trap unfortunate insects in their leaves. He even watched them sleep, folding their leaves up and down. Winding the clock forward more than 140 years, interest in how plants react to their environment, especially a changing one, is still palpable among scientists who study plants today.
Gilroy, a professor of botany at the University of Wisconsin-Madison (UW), continues Darwin’s work 250 miles above Earth’s surface on the International Space Station (ISS). He is interested in how plants react to a changing environment at the cellular and genetic levels.
“Plants are these awesome, dominant pieces of biology that solve the same problems humans solve to survive,” Gilroy said, his white hair reaching a bright red Hawaiian shirt and matching a white mustache, “but they do it in totally different ways.”
Gilroy has tested whether plants feel stressed out in microgravity and explored how they might adapt to thrive in space. Most recently, in 2021, his team launched cotton plants to the space station on SpaceX’s 22nd Commercial Resupply Services (CRS) mission. The ISS National Laboratory®-sponsored project called Targeting Improved Cotton Through Orbital Cultivation (TIC-TOC) was funded by the Target Corporation to investigate cotton root growth in microgravity.
The choice of cotton as the project’s focus is far from arbitrary. Cotton is one of the world’s most vital agricultural commodities, finding its way into myriad products, from clothing to medical supplies. But like many crops, it’s also a thirsty, hungry plant that drains resources at a time when we desperately need to conserve them. By removing the masking effects of gravity, Gilroy’s team hoped TIC-TOC would reveal genetic clues that could lead to the production of resilient cotton plants that use resources more efficiently on Earth, said Sarah Swanson, director of the Newcomb Imaging Center at UW and a microscopy and cell biology expert for Gilroy’s lab.
“If we can understand a little bit more about how cotton can grow in places that are weird and different and challenging, like the space station, it could help us make crops more sustainable and grow better under environmental stress,” Swanson said.
Roots are how plants take up water, but on the space station, plant roots grow very differently because they lack gravity as a directional cue to grow downward toward the water in the soil. Plus, there’s no gravity to pull water downward. For the experiment, Gilroy’s team explored how ordinary cotton grew in space compared with cotton genetically modified to thrive under drought conditions.
“We took cotton to a truly alien realm, where things are happening that have never happened to its biology before,” Gilroy said.
Defying the team’s expectations and contrasting many previous ISS plant experiments, the modified and regular cotton grew better in space than the cotton in a control experiment back on Earth. The modified cotton grew the largest roots and experienced the least stress in spaceflight.
It grew so well that Gilroy says it presents a new challenge: figuring out why.
Sprouting Seeds of Resilience
While simultaneously dealing with pandemic-related delays before launch, the team faced another hurdle: figuring out how to grow such a large plant on the space station. Across the Cotton Belt in the United States, cotton can reach over peoples’ heads. How would they grow it on an orbiting outpost with limited space?
“It was obvious very quickly that we needed a larger growth chamber, which didn’t exist then,” said Gilroy.
The researchers utilized expertise from the ISS National Lab and AECOM to design 12 cotton-custom growth chambers for the Vegetable Production System (Veggie) on the ISS. The clear plastic chambers contained the plants’ growth within a 10-inch long and three-inch wide space and included a translucent gel substance in place of soil that enriched the plants as they grew. “We needed to see the roots to monitor their growth,” said Swanson.
Once the cotton plants reached the ISS, the crew carefully unpacked the chambers and placed them into Veggie. Picture this: a carefully designed apparatus nurturing cotton plants as they dig deep into their genes to navigate the microgravity environment. The plants are observed by astronauts who document their growth and responses by taking high-resolution images and gathering data on how spaceflight influences the cotton’s growth and overall health.
Within just a few days, the cotton plants were already growing roots, albeit strange ones. Instead of gravity forcing the roots to grow downward, they spiraled longitudinally in search of nutrients—bunching like spaghetti in a bowl. These root systems developed even bigger than the control experiment back on Earth in the Veggie hardware inside NASA’s ISS Environmental Simulator at Kennedy Space Center, which mimics factors like temperature, carbon dioxide, and oxygen levels found on the ISS.
Plants, like all life on Earth, evolved to thrive under gravity. Without it, those grown on the space station are often slow-growing and appear stressed. “I expected our plants in space would look pretty unhappy,” said Gilroy. But that’s not what happened.
Swanson remembers when NASA astronaut Shane Kimbrough first pulled a cotton chamber from Veggie and removed the lid after the six-day experiment. “It was beautiful,” she said. “The leaves came out of the top, and the growth was amazing. We couldn’t have been happier.”
According to Gilroy, it was one of the first times that engineered plants grew better in space than regular plants. Images and data collected during the experiment and frozen cotton samples made their way home in a Cargo Dragon capsule.
When the team began analysis on the ground, the puzzle deepened.
A Puzzling Outcome
Space-grown cotton may have big roots and healthy leaves because of something intrinsic about cotton that makes it respond well to the stresses of spaceflight. “Or, perhaps, it’s something about how we grew it,” Gilroy said.
The search for an answer is revealing genetic insights that science can harness to transfer these effects to plants on Earth and improve agriculture. If the research team finds that reduced gravity in space triggered enhanced growth, Gilroy said that would provide molecular targets to genetically engineer equivalent outcomes into crops on the ground and future plants grown in space.
As the human population exploded in the 20th century, midcentury agronomist Norman Borlaug tinkered with plant genetics using mutations to create modified varieties of crop plants that grow bigger and feed more people.
Nowadays, the need to feed billions of people is paired with harsh and increasingly devastating setbacks due to the climate crisis. In fact, the researchers in Gilroy’s lab simultaneously experience extreme weather at home as they seek solutions. “This summer was a challenge,” said Swanson, who lives in Wisconsin, which experienced one of the worst droughts in its history.
But one crop that didn’t wilt under the pressure was Swanson’s backyard onions. One weighing in at three pounds won her a first-place ribbon at the Wisconsin State Fair in August. “The judge used it as a barbell,” she laughed. Whether you’re picking a type of onion to grow for a state fair, a crop to feed the planet, or plants for astronauts’ salads, she said, you want to pick the ones with a genetic code designed—naturally or through genetic modification—for what you need, such as drought resistance and size.
Scientists today have powerful genetic editing tools that allow them to tweak a plant’s natural genes with surgical precision, opening doors to improve methods for designing safer genetically modified organisms (GMOs). While GMOs have a bad reputation among some people, Gilroy says they are not harmful when backed by solid science. “You need to do your homework to ensure it’s safe before it’s released into the environment,” he explains. Turns out, the potential for homework is vast.
“There’s a tremendous number of genetic traits that we can tweak now that are going to play out as important components of agriculture,” he said.
One of these genes is AVP1, which produces an enzyme important to plant growth and stress response. Plants expressing AVP1 also have larger shoots and roots in normal conditions compared to those without it, while plants genetically modified to over-express the gene have shown increased plant growth under extreme stress, like drought. On Earth, cotton genetically modified to over-express AVP1 shows drought resistance and a 20 percent increase in fiber yield—the stuff we use to make clothes.
When the gene is expressed at higher levels, it triggers the plant’s roots to reach deeper into the ground to find water and nutrients. However, researchers are still trying to understand precisely why AVP1 triggers this response.
“We want to know exactly how this enzyme makes the cotton more resilient because that knowledge could help us improve its use as a countermeasure to plant stress,” said Swanson.
Peculiar Findings That Defy Gravity
Gravity directs roots and affects their growth, like an anchoring force in soil. By removing gravity’s influences on plant roots, TIC-TOC sought to study how AVP1 alone affects root systems and the plant’s resilience under stress. Using software to analyze images taken by astronauts in orbit, the research team conducted a quantitative analysis that showed that the AVP1 over-expressed cotton grew larger in space than the regular cotton. The space-grown genetically modified cotton also had more than four times as many roots as those grown on Earth. Genetic analysis is ongoing to determine why the cotton plants responded so well to space conditions. The team thinks the answer may relate to AVP1 influencing the cotton to regulate pH levels that help plants stay healthy.
Genetic analysis of the unmodified cotton samples from space indicates these plants were more stressed out than their genetically modified counterparts. Ordinary cotton grown in space experienced increased protein degradation and showed various biochemical markers that signal stress not found in the genetically modified cotton.
Swanson opened a photo on her desktop of a green cotton field with a reddish-brown spot in the middle of it the size of a swimming pool. “What do you think it is? Strange, right? It’s the scene of a lightning strike,” she said, explaining that the unmodified cotton grown in space showed similar signs of increased pigment under stress. In contrast, the genetically modified cotton did not.
The genetically modified cotton grown in space also showed other changes in genes related to processes not observed before in regular cotton and generally not reported as spaceflight-related responses. Further investigation may show that these changes are related to the plants’ resilience. But, overall, genetic analysis of the space-grown cotton found plenty of responses typical of plants grown in space, especially the plant Arabidopsis thaliana, a relative of cabbage commonly used in plant biology as a model organism.
“That is a big plus for us, as it says that even though cotton is only distantly related to these other plants that have been grown on the space station, they are all showing similar responses,” Gilroy said. “That means the results all look to be pretty robust indicators of what plants can do in space.”
According to Gilroy, the findings show that AVP1 is a vital gene to explore as a countermeasure to the stresses of spaceflight. It’s a promising new tool for growing plants during long-term space missions to keep astronauts healthy and for growing food on a nearby planet one day.
Because both regular and modified cotton grew better in space than back on Earth, Gilroy says this must mean the growth effect is also directly related to the space environment and how they grew it. It’s possible, he said, that once the cotton-customized hardware mitigated the stressful effects of spaceflight, other features of microgravity may have encouraged the plants’ growth. Or maybe it’s something to do with cotton itself.
By decoding why cotton grows better in space than on Earth, Gilroy’s team may be able to write a new chapter in farming, one that enhances our crops on the ground and in space.
At this point, though, the story is unfinished. “What is magic about cotton that isn’t seen in other plants grown in space?” asked Gilroy. “At the moment, we don’t know.”
It’s a mystery beyond Darwin’s wildest dreams.