CSU biologists and engineers create genetic toggle switch for plants | Walter Scott, Jr. College of Engineering | Colorado State University
CSU biologists and engineers create genetic toggle switch for plants
By Taryn Bradley and Russell Dickerson
May 22, 2025
If you’re one of the folks who looks forward to pumpkins every fall, the long summer wait can be tough. For farmers, the summer might become a huge issue if climate change leads to more drought in the crucial growing season.
What if farmers could instead choose to ripen them in June with just the flip of a switch? Groundbreaking CSU research could someday help farmers make that a reality.
Researchers working with Professor June Medford, in biology, and Professor Ashok Prasad, in chemical and biological engineering, collaborated to create a “toggle switch,” using genes that can target specific traits in plants and turn them “on” or “off.” Their interdisciplinary research was
recently published in the journal ACS Synthetic Biology
The genetic toggle switch acts similarly to a circuit in electronics, and is made possible by synthetic biology – the marriage of biology and engineering.
The biology of genetic toggles
“A genetic circuit is just a big piece of DNA that we have inserted into a plant that allows us to regulate whatever trait we want, such as controlling flowering so that a tomato plant ripens all at once,” said Medford.
Up until now, genetic circuits have only been used in single-celled organisms. Applying this principle to plants is a little more difficult, said Tessema Kassaw, a research scientist in the Medford lab and a first author on the paper.
“Part of the challenge is the lifecycle of plants, which have a relatively long lifecycle compared to bacterial systems that genetic circuits have previously been used with,” said Kassaw. “Also, the multicellular nature of the plant – their roots, tissues, vegetative and reproductive organs- makes it complex.”
The process began in the Medford lab where Kassaw assembled genetic components – the genes that affect the traits and characteristics of plants – and tested them in singular plant cells. Kassaw made hundreds of genetic components, totaling more than a million possibilities of pairings.
“This is where the math came together with Prasad’s lab because they would tell us mathematically which pairings would give us the best functions,” said Medford. “So instead of testing about a million possibilities, we could just try two or three.”
Kassaw then translated the data from the Prasad lab into a living plant by injecting it into the plant and seeing if the desired traits could be toggled on and off. The Medford and Prasad labs would go back and forth tweaking the genetic components, testing them in plant cells, quantifying the data, and then testing it in the whole plants.
“Sometimes working with plants is like watching the grass grow,” joked Medford.
The team went through a series of toggle switches to strike a balance of the right genes and quantities for the desired outcome. For example, in the 2.0 version of the switch, a trait could be turned on, but it couldn’t be turned off again.
“As biologists, we understand biology really well, but we partner with folks like Ashok Prasad and Wenlong Xu who understand math and engineering, and aren’t afraid to find the signal amid the noise,” said Medford. “In doing so, we now have the ability to make switches.”
Professor June Medford
Research scientist Tessema Kassaw
Sometimes working with plants is like watching the grass grow.
June Medford
Engineering new circuits
Finding that signal amid the noise is where synthetic biology comes in. In this case, it means engineering a living organism to do something different, based on measurement, mathematical modeling, genetic manipulation, and many iterations.
The Prasad lab used mathematical modeling to identify two things. First, they had to know the inner workings of normal circuits that control a plant’s biology. Then they could make a synthetic circuit  to make the plant do something different.
After each circuit, the lab measured the results and applied math, over and over again, to make sure that the proteins interacted with one another. Collecting quantitative data is important at this step so researchers can observe whether the protein interacts the way they need it to.
“Trying it without data and analysis is equivalent to taking a piece of silicon, shoving it into an electronic circuit board and saying, ‘here’s my transistor.’ Obviously, no one does it that way,” said Prasad.
The complexity of living organisms limits how much genetic material researchers can add to a plant, and how they can manipulate it. Wenlong Xu, a graduate student in Prasad’s lab during the research and a first author on the paper, used image processing, data analysis, and modeling to work with the Medford lab on iterations within those limits.
“Scientifically, the biggest hurdle was convincing myself that quantitative synthetic biology could work in a multi-cellular, long-generation organism,” said Xu. “Personally, the challenge was staying patient and optimistic through the long turnaround time of the plant cycles.”
For Prasad, the step-by-step, iterative process of the research opens up the next challenge: being able to eventually manipulate plants with other types of circuits.
Professor Ashok Prasad
Research scientist Wenlong Xu
Scientifically, the biggest hurdle was convincing myself that quantitative synthetic biology could work in a multi-cellular, long-generation organism.
Wenlong Xu
Watch a genetic switch in action as it turns on a light-emitting protein.
To test the genetic switch, researchers used it to control the level of a light-emitting protein. This animation shows images of a plant when the switch was turned on using an external signal, taken by a special camera.
Video Caption
No sound in video. Title shows Colorado State University logo with text, “Genetic Toggle Switch in Plants.” Images appear from day zero to day ten as the plant grows, with text “Inducer added” between day six and seven. Authors are listed at bottom, Tessema K. Kassaw, Wenlong Xu, Christopher S. Zalewski, Katherine Kiwimagi, Ron Weiss, Mauricio S. Antunes, Ashok Prasad*, June I. Medford*.
A future of possibilities
“What we find is that different types of circuits are suited for different purposes, which is, of course, exactly the way it happens in living organisms,” Prasad said. “Can we control the composition of the fruit by controlling some aspect of metabolism that’s going into the fruit?”
Medford and Prasad describe the research as “a proof of concept,” and expanding how the circuit is used can lead to many other possibilities.
“In the future, you could see how you could do this using methods to directly edit the plant genome,” Medford said.
This project also offers promising outcomes for the agriculture industry in the face of unpredictable and unseasonable climates.  Farmers could control the state of their crops by turning “on” the toggle switch to signal to the plants when it’s time for them to ripen for harvest. If drought altered the fall pumpkin harvest, for example, using the switch could help them grow earlier and retain size and nutrition.
Medford and Prasad joked that one day they could manipulate the astonishingly massive pumpkins seen nationwide every fall in the news, weighing tons and almost the size of a small car.
“Imagine that you could actually change how carbon goes into those pumpkins, and have a pumpkin that is essentially a giant batch of oil,” said Prasad. “I mean, that would be quite something.”
In the future, you could see how you could do this using methods to directly edit the plant genome.
June Medford
Professor June Medford, research scientist Tessema Kassaw, and Professor Ashok Prasad discuss plants in a lab within the CSU Biology Building in May 2025.
Related Stories
channel-walter-scott-jr-college-of-engineering
College of Natural Sciences
Department of Biology
Department of Chemical and Biological Engineering
Faculty
Research
Walter Scott Jr. College of Engineering
SOURCE Contributor
More posts by SOURCE Contributor