Researchers from Michigan State University recently completed a comprehensive study of the genomes of several species of mint plants , to trace their evolutionary pathways at the chemical level. These scientists hope their work will have many practical applications, providing useful information to researchers looking to develop medicines, antimicrobials, and organic pesticides from mint.
The mint family of herbs includes sage, rosemary, basil, thyme, lavender, catnip, oregano, peppermint, and dozens of other plants that can stimulate the human senses of taste and smell. Mints have traditionally been used as flavorings for foods and drinks, to make scents for perfume, for oral hygiene, and as herbal medicines.
Members of the mint family have been used in numerous ways, from food to hygiene to medicine. ( Yanadjan / Adobe Stock)
As Michigan State researchers explain in an article just published in the journal Nature Communications , they were interested in looking more closely at the DNA of various mint plants to see how they developed and diversified. This process of diversification has produced an immense variety of species with their own distinct characteristics.
As it turns out, it is the mint plant’s need to defend itself that drove it to evolve in so many different directions.
“People easily recognize members of the mint family for their specialized metabolites,” biochemist and study co-author and Björn Hamberger said in a Michigan State University press release . “Metabolites are an efficient way for plants to defend themselves because they can’t run away.”
In many green plants, it is a type of metabolite known as terpenoids that help prevent them from being eaten by voracious predators. Terpenoids are present in all plants, and are responsible for plant coloring and aroma. They also give plants a unique taste when they’re eaten.
While the odors they emit and the tastes they create can be attractive to humans or pollinating insects, the chemicals in the terpenoids are often repellent or toxic to insects, fungi, bacterial parasites, and animals that would consume or infect the plants that produce them. Terpenoids developed their protective capacities over millions of years through evolution, and the members of the mint family can all make unique terpenoids that protect them against the enemies in their ecosystems.
Because of their specialized chemical profiles, terpenoid metabolites can be used as food or cosmetic additives, as healing compounds, dental protectors, pesticides, or antimicrobial agents that shield crops from predator destruction. Scientists study the DNA of plants to learn more about the specific qualities of their terpenoids, and the Michigan State researchers involved in the new study were seeking to unlock the secrets of mint’s DNA, which is believed to have enormous untapped potential to produce many substances that would be beneficial to humans.
New research on the mint family’s terpenoids yielded exciting new potential uses for mint. ( adidas4747 / Adobe Stock)
Uncovering the Beautiful Secrets of the Beautyberry Plant
For the past several years, Björn Hamberger and Robin Buell, a former MSU genetic researcher who is now at the University of Georgia, have been working to sequence the DNA of multiple species of mint plants. With support from other MSU researchers and graduate students, the scientists were able to track the evolution of mint plant genomes over an incredibly long period of time (60—70 million years).
“Over millions of years, plants have adapted and evolved for their particular niches where they thrive, and that means that these chemistries are diverse and have clearly adjusted to their environment,” Hamberger said. “So, we try to identify and discover pathways to these specialized metabolites that plants make.”
Two graduate students, Abigail Bryson and Emily Lanier, were able to identify the genes in mint plants that were responsible for the biosynthesis (creation) of terpenoids. While studying the genome of a type of mint known as a beautyberry, the two researchers found it contained a large gene cluster known as the BGC group. This distinctive set of genes has been observed in bacteria many times, but its role in the plant world is not well understood.
Looking more closely, Bryson and Lanier found different versions of the BGC group in six other species of mint, all of which had a special place in the genome.
“We are learning that the physical location of genes within the genome is important,” Bryson said. “It can drive evolution of specialized metabolic pathways in the plant, leading to a vast diversity of interesting natural plant compounds .”
Through further study, the researchers discovered that the BGC cluster in the beautyberry plant is involved in the creation of two different kinds of terpenoids. They found dense accumulations of these terpenoids in various parts of the plant, including the leaves and roots, which are vulnerable to attack by pests and predators.
“It’s the same base molecule, but each species is making its own version and modifying it in different ways to fit their survival needs,” Lanier said, referring to the terpenoids.
With the ability to adapt to living in all types of ecosystems, mint plants can diversify into a broad range of species, many of which will look, smell, and taste quite different from their cousins.
The aptly-named beautyberry is a member of the mint family, which recently was the source of an insight on the metabolic pathways of the mint family. (Ken Mattison / CC BY NC ND 2.0 )
The Uses for Mint through the Ages
Mint plants are currently being used to treat certain types of medical conditions. To give a couple of examples, Indian Coleus is often applied as a treatment for glaucoma, while Texas sage has antimicrobial properties that have made it useful as a remedy for tuberculosis.
But modern researchers didn’t just suddenly discover the health-protecting capacities of mint.
The plant was referenced 3,500 years ago in an ancient Egyptian medical text known as the Ebers Papyrus , which prescribed it as a cure for bloating and flatulence. More than a thousand years later, physicians in Greece, including the famous Galen, were recommending mint plants as a safe and effective form of oral contraception for women. Mint has been used in traditional Chinese medicine for more than 2,000 years, and in fact, a 2019 research project successfully sequenced the DNA of a type of medicinal mint known as Chinese Skullcap , which researchers believe could allow the plant’s chemicals to be used to develop many new therapeutic applications.
Chinese skullcap, pictured, has been used in traditional Chinese medicine for thousands of years. (Agnieszka Kwiecień, Nova / CC BY SA 4.0 )
In medieval Europe, mint was widely celebrated for its healing properties. A 17th century text written by Nicholas Culpepper, an English astrologer and apothecary (or pharmacist in today’s terminology) claimed mint could be used to treat more than 40 ailments!
In the present day, the new information Michigan State University researchers have discovered about terpenoid chemistry could help them develop brand-new products derived from mint plants.
“Our team has been excited about the opportunities within the mint family,” Björn Hamberger said. “Those mint enzymes, as in the American beautyberry plant, give us the ability to make plant-natural products in the lab, including—hopefully in the future—natural good-smelling mosquito repellants.”
Top image: Beautyberries (left) have revealed insights about mint family composition. Source: Left: Tom Cardrick / Adobe Stock; Right: Public Domain
By Nathan Falde