Fragrant garden staples part of the sprawling mint family like thyme, basil and lavender are hiding some super-sized secrets with big applications, according to Spartan researchers.
While unraveling the genetic makeup of a mint relative called ground oak, MSU biochemists discovered it sported a truly massive genome — nearly as large as our own — as well as an extra-large gene cluster and four sets of chromosomes.
Mint plant family members are known for their natural anti-cancer, anti-pest and anti-viral properties and by unraveling ground oak’s genetic mysteries, researchers are one step closer to reproducing these naturally powerful plant chemicals in the lab.
“What if we could spray our veggies with a natural product that makes a hungry deer or insect say, ‘No thank you,’” MSU researcher Björn Hamberger said, noting potential uses in large-scale agriculture.
“These plants also have exciting antimicrobial properties, which could help with the trouble we see nowadays concerning antibiotic resistance,” he added.
The team’s findings, which appear in the journal Plant Communications, were made possible by funding from the National Science Foundation, the National Institutes of Health and the U.S. Department of Energy-supported Great Lakes Bioenergy Research Center.
“This project was like many others where we walked in thinking we knew just what to do,” Hamberger said. “We’ve learned again that plants always have something more up their sleeves.”
A family reunion
Humans have made the most of the mint family’s dazzling chemical diversity for millennia, from medicine and fragrances to well-known culinary uses.
At MSU, Hamberger studies these eclectic chemicals, better known as specialized metabolites — and particularly a group of molecules called terpenoids.
Specialized metabolites are molecules that plants evolve to give them an extra edge in their environment. These are different from primary metabolites, which are the molecules a plant needs for basic survival processes like growth and reproduction.
You might think of this molecular mix as the ingredients needed to bake a cake.
If primary metabolites are the flour, butter and sugar that form the cake’s foundation, specialized metabolites are flavors like chocolate or vanilla that make it totally unique for each occasion.
When a plant finds its ecological niche and inhabits it for tens of millions of years, it’ll evolve a treasure trove of specialized metabolites to adapt and thrive.
These highly unique molecules are the sources of exciting chemical properties seen across the mint family, whether its Indian Coleus’s ability to treat glaucoma, or Texas sage, whose antimicrobial chemistry can be used against tuberculosis.
“Plants don’t have the luxury of running away from pests or pathogens, so they turn to chemistry to get the job done,” said Hamberger, the James K. Billman Endowed Professor in the Department of Biochemistry & Molecular Biology.
Previously, the Hamberger Lab made major breakthroughs by exploring this genetic and chemical variety.
In 2023, his team unpacked the genome of American beautyberry, a shrub with bright magenta berries whose native chemistry repels mosquitoes and ticks. This helped shed light on how the mint family had diversified its chemistry across the ages.
The research, which ultimately looked to synthesize compounds that could be used as cost-effective pesticides, earned Hamberger lab members Abigail Bryson and Nicholas Schlecht MSU’s Neogen Land Grant Prize.
Awarded by my MSU’s Office of Research and Innovation, the prize highlights graduate students whose research will contribute to the scientific and economic improvement of society.
On the hunt for further scientific surprises in the mint family, Bryson chose the understudied ground oak as the lab’s next target. Found throughout the Mediterranean basin, this mounded shrub with pinkish purple flowers earned its name for the shape of its tiny leaves.
“We thought: let’s sequence ground oak, find out how the plants achieve their useful chemical products and get a blueprint to build plant-derived therapeutics in the lab,” Hamberger said.
“This was all good, until Abby found out ground oak had an unexpectedly massive surprise in store for us,” he added.
Puzzles and clusters
In the commonly studied plant Arabidopsis, you’ll find a modest 135 million base pairs of DNA.
So, imagine Bryson and Hambergers’ surprise when it was revealed their ground oak contained some three billion base pairs — nearly as many as the human genome.
To wrangle these massive genetic sums, Bryson honed her bioinformatic skills working alongside Robin Buell, a former MSU Research Foundation Professor and current Georgia Research Alliance Eminent Scholar Chair in Crop Genomics at the University of Georgia.
“When you assemble a genome, it’s like you have parts of sentences of a book and you are trying to figure out what the story says, line by line, chapter by chapter,” Bryson said, the paper’s lead author and a current postdoctoral researcher at the Donald Danforth Plant Science Center.
“Something about genomes that is difficult to picture is the size of the data we are working with. If the genome was the size of an actual book, the thickness of that book would be hundreds of feet and the human and ground oak genomes would be around the size of world’s fifth tallest building,” she added.
The group’s research efforts further benefited from Department of Plant Biology collaborators Kevin Childs and Jiming Jiang and made use of MSU’s Max T. Rogers Nuclear Magnetic Resonance facility.
On top of the eye-watering size of the ground oak genome, the team encountered extra surprises that helped fill in the picture of just how the mint family evolved its potent natural chemistry.
“We found that ground oak is a tetraploid, meaning it has four copies of its genome. By comparison, we humans are diploid, so we have two — one from mom and one from dad,” Bryson said.
“Imagine if you have to sort through and solve four puzzles dumped into the same box — that’s what Abby achieved,” Hamberger added, noting the challenges of sequencing such a complex genetic landscape.
There was also the revelation that ground oak contained an incredibly large gene cluster. This is a genomic region where genes with similar functions are located close together.
The Hamberger Lab found a similar, smaller cluster in their earlier study of American beautyberry, leading them to believe this cluster is evolving dynamically across many mint family plants.
But why double or group up your genes in the first place? Hamberger says it comes down to plain old evolutionary efficiency.
If one set of genetic information is already performing an important duty, its duplicate is free to evolve newer functions.
As for having similar genes grouped together, Hamberger compares it to having your checked luggage reach the correct destination after multiple flights.
“Once materials are packed together tightly, it’s easier to move them onto the next generation,” he explained.
With these latest findings, the Spartan biochemists are taking the next step toward reproducing powerful, naturally occurring molecules in the lab in useable quantities.
So, the next time you encounter a mint relative on your table or in the garden — whether it’s oregano, rosemary or even catnip — remember you’re looking at a plant whose chemistry could help us take on the world’s grand challenges.
This story originally appeared on the College of Natural Science website.