By Marisa Sloan
It’s been said that talking to plants can help them grow, but plants may soon be able to talk back. While teaching biology at The University of North Carolina at Greensboro (UNCG) over twenty years ago, Dr. Neal Stewart Jr. envisioned a future where plants could produce visible signals if they detected an abnormality in their immediate environment. On Nov. 6, Stewart returned to UNCG once again to discuss how his dream is being actualized in agriculture.
At the University of Tennessee Institute of Agriculture, Stewart’s research group focuses on altering the DNA of plants, animals and microbes of agricultural importance.
“Synthetic biology is basically a hybrid between engineering and computational strategies, in order to design DNA and make a more complex DNA sequence,” said Stewart. “One of the things that we’ve done is we’ve computationally designed a DNA library that we’re now screening.”
That library currently consists of over 2000 synthetic promoters. For the transcription and subsequent translation of a gene to take place, a promoter attached to the gene must first serve as an on-off switch. Synthetic promoters are comprised of fragments of natural promoters that form new DNA sequences, and initiate gene activity based on the plant’s needs.
“That’s making plants that can tell you where landmines are. You sow a field full of seeds, and you look for the fluorescent protein plants when you fly over with your laser.”Dr. Neal Stewart Jr.
For example, Stewart attached a promoter that turns on when the plant is in need of water to a gene that helps the plant endure without it.
“Basically, we’re hooking up the drought-stress promoters, the ones that get turned on, with genes that now help the plant survive the drought stress,” said Stewart. “We know what these genes are, but if they’re expressed all the time in the plant, the plant doesn’t like it. We just need them to come on and then go off.”
Stewart’s library also includes synthetic promoters initiated by stimuli such as radiation, heavy metals in the soil, and certain bacteria and pests. But the ability of a plant to sense these disruptions in its environment is even more agriculturally beneficial if it can simultaneously report it to the person responsible for its care.
Fluorescent proteins, proteins that glow when exposed to ultraviolet light, are commonly used to monitor if a promoter is active and initiating the expression of a specific gene. To do this, researchers sandwich a fluorescent protein gene between the promoter of interest and the gene that the promoter controls. If the cell glows, it means the promoter has turned on and initiated the translation of both the fluorescent protein and other gene.
The most frequently used fluorescent protein is green fluorescent protein (GFP), which was first cloned 30 years ago from a jellyfish. Since then, many organisms have been genetically engineered to glow green: a mouse, a frog, a rabbit and a monkey. In 2003, it even became possible for anyone to own their own genetically modified pet with ‘GloFish’, glowing zebrafish that were sold at pet stores for a mere $5.
Stewart said that he was the first to express GFP in plant leaves that could be seen with ultraviolet light. Since then, he has developed a wide range of fluorescent proteins that glow specific colors depending on which wavelength of ultraviolet light is shined. This could potentially allow a single plant to be engineered to have several different synthetic promoters, each with their own colored fluorescent protein, and signal multiple environmental disruptions simultaneously.
Current instruments used to detect plant fluorescence include ultraviolet spotlights and flashlights, as well as laser-based instruments for detection from large distances such as from aircraft or survey towers. Such long-range tools would be beneficial in commercial agriculture, where it is necessary to monitor vast geographical areas, but Stewart can see other potential applications for his technology as well.
“Another one is explosives, and that’s been my dream project since day one,” said Stewart. “That’s making plants that can tell you where landmines are. You sow a field full of seeds, and you look for the fluorescent protein plants when you fly over with your laser.”
Although he has attempted to do so with little success over the past two decades, Stewart is confident that the recent advancements in synthetic biology will soon change that.
“I’m still hopeful,” said Stewart.