Grow-in-the-dark crops could feed astronauts in space and nourish Earth's growing population. A compact version of a tomato plant developed at UC Riverside is expected to reach astronomical heights. Growing only a few inches tall, this genetically engineered crop is setting a course for the International Space Station, orbiting some 260 miles above Earth. It is now undergoing observations at NASA's Kennedy Space Center in Cape Canaveral, Florida, and its seeds are in line for a payload flight within the next year or so.
Its voyage will be a generational first: The seeds will germinate in the station's Advanced Plant Habitat laboratory, produce fruit, and the seeds of that fruit will be planted again to create a second generation of tomatoes grown in space.
"So, it's going to be a seed-to-a-seed-to-a-seed, which has never been done before in space," said Robert Jinkerson, an associate professor of chemical and environmental engineering in UCR's Marlan and Rosemary Bourns College of Engineering. The tomato is designed to produce fruit in small spaces so it can be a food source for astronauts. It has been years in the making.
Firstly, Martha Orozco-Cárdenas, director of the Plant Transformation Research Center in UCR's College of Natural and Agricultural Sciences, used CRISPR-Cas9 gene-editing technology to downsize ordinary tomato plants and reduce the ratio of leaves and stems to fruit. Then, with support from an $800,000 grant from the NASA-funded Translational Research Institute for Space Health, Orozco-Cárdenas and Jinkerson further engineered and evaluated the plants to determine their space worthiness. Dubbed Small Plants for Space Expeditions (SPACE) by the researchers, the technology could be applied to other plants to develop a suite of crops for agriculture on the International Space Station and future space colonies.
Cosmic cultivation
Tomatoes may not be the only homegrown produce on the space station's menu. Jinkerson and his team are also developing systems to allow for edible yeast, green algae, and mushrooms to be grown in space.
This summer, the team won $250,000 toward their research as a runner up in NASA's Deep Space Food Challenge, an international competition that started with about 200 teams of scientists to develop systems to produce food on the International Space Station. The proposed technology was limited to 2 cubic meters — about the space of a small closet — and could use no more than 1,500 watts of electricity.
To create such a compact system, the UCR team built on its success in the laboratory of growing mushrooms without sunlight. Instead of relying on photosynthesis — the natural process of using energy from sunlight to turn carbon dioxide in the atmosphere into sugars — the mushrooms use a carbon-based compound called acetate as an alternative energy source.
"With our system, we estimate we can get about 4,000 calories per day," Jinkerson said. "It's a lot more than you could do with biological photosynthesis."
Down to earth
Jinkerson's research also has more earthly implications. Crops that can grow efficiently in tight indoor spaces are needed for urban agriculture. Using indoor "vertical" farms, hydroponically fed crops grow on racks with as many as a dozen layers, and each layer allows for only about a foot of growing space. Because of the height limitation, indoor farms in the U.S. so far have been mostly limited to growing salad greens, such as spinach and baby lettuce. But a version of the UCR-developed SPACE tomato could be in the offering.
Indoor agriculture innovations are also needed to grow crops in regions where the climate is becoming too inhospitable to grow crops outdoors, such as increasingly dry regions in Africa. Toward that end, Jinkinson has received a $2.4M grant from the Bill and Melinda Gates Foundation to develop crops that grow using acetate.
"We can cultivate food-producing organisms in the dark with acetate as their sole source of carbon and energy without any inputs from photosynthesis," Jinkerson said.
Jinkerson's lab-grown mushrooms rely on acetate instead of sunlight. (UCR/Stan Lim)
Jinkerson and his graduate students have successfully grown yeast, mushrooms, and green algae in the dark by feeding these organisms acetate. Growing tomatoes and other crops in the dark with acetate, however, is proving to be more of a challenge because acetate is toxic to adult plants. Jinkerson's team is homing in on solutions that involve mimicking metabolic processes found in germinating seeds. As seeds germinate, they can process acetate, but this mechanism shuts off as soon as the sprouts hit sunlight.
"We're basically trying to do engineering to turn on the metabolism that enables the adult plants to use the acetate," Jinkerson said. "We're overexpressing key enzymes that give the plants more tolerance."
Producing food in the dark could potentially revolutionize agriculture by allowing for more widespread indoor cultivation wherever electricity is available for electrolysis.
Terrestrial limitations
Photosynthesis may be miraculous, but it is also energy inefficient, Jinkerson said. Consider a field of densely planted soybeans: Only about 1% of the solar energy landing on the field is captured by plants to produce biomass. Cover the same field with photovoltaic solar panels, and you'll capture 22% of the sun's energy in the form of electricity generation. That captured energy could then be used for an electrolysis process to turn carbon dioxide into acetate. Once that acetate is used to produce crops in the dark, as much as 8% of the sun's original energy goes into biomass, Jinkerson's research has shown.
Agriculture had a great run in the 20th century, Jinkerson said. Food production per acre doubled thanks to more productive crop varieties and incremental breakthroughs in fertilizer, pest control, and irrigation technologies. Yet agriculture is now reaching physical limitations and production is leveling off while the population continues to grow, and farmers face new challenges from climate change.
Could growing crops indoors in the dark be the next technological breakthrough? Jinkerson believes so.
"Using artificial photosynthesis approaches to produce food could be a paradigm shift for how we feed people. By increasing the efficiency of food production, less land is needed, lessening the impact agriculture has on the environment." Jinkerson said. "And for agriculture in nontraditional environments, like outer space, the increased energy efficiency could help feed more crew members with less inputs."
Read more at: ucr.edu