Hacking Photosynthesis

Traditional agriculture requires large landmass areas and plenty of sunlight—two inputs that are clearly limited in deep space. Over half of the U.S. landmass is used for agricultural purposes. The fact that plants convert less than 1% of solar energy into edible calories presents a major limitation for crop yields, especially in photon-limited environments like spacecrafts, the Moon, or Mars. Something we all learn in biology is that plants use light photons to convert the carbon dioxide (CO2) from air into sugars and energy that lets them grow, a process called photosynthesis. Today, however, some scientists are questioning that seemingly fundamental paradigm and looking for ways to increase the energy efficiency of plants by cutting out photosynthesis.

Robert Jinkerson, a professor of Chemical and Environmental Engineering at UC Riverside, has figured out a way to grow plants in the dark. His team, together with Feng Jiao’s group at Washington University in St. Louis, has pioneered a new field of electro-agriculture that allows for direct conversion of atmospheric CO2 into plant biomass—without the light.

This method was developed back in 2021 as a part of the Deep Space Food Challenge, a competition sponsored by NASA and the Canadian Space Agency. At its core are two main technologies: a device called an electrolyzer, which turns CO2 into acetate, and genetically engineered plants that can use that acetate to grow in the absence of light. The direct electro-chemical conversion is more energy efficient than traditional agriculture, which is especially important for plants grown indoors under artificial light.

“When you grow plants indoors, that's where our process really shines,” Jinkerson explains. “In controlled environments like vertical farms or greenhouses, using electricity to convert energy into light with LEDs is not the most efficient way because plants waste the majority of that energy.”

Coaxing plants to use acetate for energy instead of photosynthesis is not an easy feat. To do this, scientists used multiplex CRISPR editing to rewire plant metabolism. Seeds use stored nutrients like carbohydrates and fats for growth when they are underground. Once the seedlings emerge into the sunlight, however, they switch to photosynthesis. CRISPR enables scientists to reawaken those dormant metabolic pathways that exist to germinate seeds.

Initially, Jinkerson’s team tested this approach not in plants, but in mushrooms, yeast, and algae grown in the dark. They calculated an eighteen-fold increase in efficiency with this method. They also showed that plants including lettuce, tomatoes, and peppers raised in the dark can incorporate acetate labeled with carbon-13 (a heavy isotope of carbon) into their tissues. Although plants fed acetate stayed alive, the energy gains were not high enough to allow them to grow in size.

The team has been improving the plants’ genetics to make them more efficient at converting acetate to biomass and tested them on the International Space Station during a 30-day experiment last year. Alongside that project, Jinkerson is working with a UC Riverside professor, Martha Orozco-Cardenas, and Gioia Massa, a program manager at NASA’s Kennedy Space Center, to develop energy-efficient SPACE tomatoes (short for Small Plants for Agriculture in Confined Environments) engineered to have smaller leaves and stems while bearing more fruit.

Bringing Innovation From Space Back Down to Earth

Besides limited space and light, growing food in space presents other unexpected difficulties. In the absence of gravity, even watering plants becomes an engineering challenge. Heat and moisture accumulate around the leaves, stems, and roots of plants, and supplementing soil with acetate exacerbates the risk of microbial contamination.

Researchers at NASA have designed special ‘plant pillows’ to solve this problem. Interstellar Lab, an American-French biotechnology company, has come up with an alternative approach: the startup is developing closed-loop systems that recycle air, water, and nutrients to support the cultivation of plants, mushrooms, and even insects. Interstellar Lab was the winner of the 2024 Deep Space Food Challenge. Their next ambition—dubbed ‘Mission Little Prince’ after Antoine de Saint-Exupéry’s book—is to grow roses on the Moon.

These innovations, while initially designed to enable space exploration, could also help address food security issues here on Earth by supporting food production in densely populated areas, harsh environments, or under disaster scenarios. Acetate supplementation could replace vertical farming, which has been largely unsuccessful, and enable the use of plants as factories for producing pharmaceuticals, vaccines, or other high-value ingredients that improve our health—all without competing for farmland.

“In one to two hundred years, our agriculture will look very different,” says Jinkerson. “We'll be able to produce food in highly controlled environments, and it's going to be much more sustainable. For example, we could produce just the part that we're eating, without the whole plant.”

It sounds ambitious. But if you think about it, almost every innovation we take for granted today started out as a moonshot.

Thank you to Katia Tarasava for additional research and reporting on this article.