In addition to being a symbol of love and romance, roses are also known for being sharp — thorns protrude from the stems to ward off animals that try to chew on the buds.
They are not the only plants with this defense mechanism: Bougainvillea, popularly known as spring, the crown of thorns, even used to protect fences, in addition to the flowering shrubs responsible for giving us raspberries and blackberries, several plants have sharp tips.
But why do all these species, many of which evolved separately over millions of years, have the same spiny feature? A team of international researchers has found that the answer lies in their DNA, tracing the origins back to an ancient family of genes responsible for the spines in all these variations, according to a new study published Thursday. in the journal Science.
The findings not only open the door for scientists looking to create spineless variants of these species, but also provide insights into the evolutionary history of an extremely diverse genus of plants, experts say.
The evolution of “thorns”
Contrary to popular culture references, roses do not have thorns, which are actually the sharp, hard, dry tips of certain shrubs, trees, and, of course, cacti. Instead, the flowers have prickles, which form from the plant’s epidermis in a process similar to how hair grows.
Thorns have been around for at least 400 million years, first appearing on the stems of ferns and their relatives. Since then, the trait has appeared — and disappeared — at different points in evolutionary time, explained study co-author Zachary Lippman, a plant biologist, professor of genetics at Cold Spring Harbor Laboratory in Long Island, New York, and an investigator at the Howard Hughes Medical Institute.
One of the most diverse plant genera known, Solanum — which includes crops like potatoes, tomatoes and eggplant — first developed thorns 6 million years ago. Today, the genus has more than 1,000 species that occur worldwide, with about 400 of them having thorns, according to the University of Utah.
When a common trait, such as spines, appears independently in different lineages and species, it is what we call convergent evolution. This occurs when species adapt in similar ways to meet certain environmental needs.
Wings are another example of a trait that evolved this way among different species of birds, as well as other animals such as bats and even some types of squirrels that have a wing-like structure, Lippman said.
Spines and thorns are defenses that emerged during evolution to protect species from herbivores — animals that eat plants — and can also aid in growth, plant competition and water retention, according to the study.
It wasn’t known exactly what caused ferns and other unrelated plants to develop thorns. Now, the study authors have discovered that an ancient gene family known as Lonely Guy, or LOG, served as a gatekeeper for the trait, causing it to appear and disappear in different species over millions of years.
Thorny genes
By removing the spines from several species, including roses and eggplants, the authors found that a LOG gene was responsible for the spines in about 20 types of plants studied. Genes related to LOG are found in all plants, even mosses, which are considered the first dry-land plants, Lippman said.
The genes are responsible for activating a hormone known as cytokinin, which is important for a plant’s basic functions at the cellular level, including cell division and expansion, which in turn affects plant growth.
“It’s not like there was a common ancestor that had spines, and they spread over 400 million years to all these other [plantas]and then they were sporadically lost. In fact, what it looks like is that they seem to pop up quite readily in different lineages,” Lippman said. “Now the question is, how often is convergent evolution not just the trait that we see, but the genes behind the trait?”
He added: “Our study is, I think, probably the first to really demonstrate the power of these tools [sequenciamento genético e genômico] to span such a wide evolutionary distance and ask this very classical question about convergent evolution in plants or animals.”
The discovery adds a valuable tool for researchers seeking to understand the extent to which spines provide protection against herbivores. That level of defense has previously been challenging to assess, since manually removing spines from already-grown plants — to test whether they are more vulnerable without them — damages the tissue and can compromise the health of the plants, said Tyler Coverdale, an assistant professor of biological sciences at the University of Notre Dame who was not involved in the new study.
“By eliminating thorns with targeted genetic mutations, we can more fully understand the ecological role of plant physical defenses,” Coverdale said in an email.
“Spines are an essential evolutionary development that allows plants to resist herbivory, which is why many of the spine-bearing plants in the genus Solanum are found in areas with historically high diversity of large herbivores. Without this essential innovation, it is possible that the genus Solanum would be much more restricted in its range and diversity,” Coverdale added.
Removing thorns genetically
Before this discovery, another method used to try to remove thorns from plants was to try to cross the plant with another variety that had lost its thorns naturally, Lippman said, which is why there are now some rose species without thorns.
But now that the gene responsible for the thorns has been identified, scientists can remove them using genome editing techniques like CRISPR, a method scientists use to modify the DNA of living organisms.
Targeted gene editing can create more variation easily and has fewer consequences on plant growth and fruit production, Coverdale said.
“This study not only tells us more about the evolution of spines specifically, but also provides us with insights into the mechanics of how to engineer plant developmental pathways for agricultural improvement,” said Vivian Irish, a plant biologist and professor in the department of molecular, cellular, and developmental biology at Yale University. Irish was not part of the new study, but she was the senior author of a 2020 study that found spines grow in plants through stem cell activity.
“[Os genes LOG] were repeatedly co-opted [uma mudança biológica na funcionalidade de uma característica] in different plant species for the formation of spines, and also repeatedly lost in lineages where spines are lost,” she said.
“Co-option at many different levels may be the rule of thumb of nature, and this innovation in many cases may well reflect the reuse of old genes in new ways,” she added in an email.
For agricultural purposes, removing the thorns can make harvesting easier and pave the way for lesser-known products to reach supermarkets.
One example the authors use is desert raisins, which are fruits grown on thorny shrubs native to Australia. With the thorns removed, the fruit could be grown much more easily and would be more similar to common supermarket fruits such as blueberries and strawberries, Lippman said.
“It’s really about having more knowledge … and understanding how important mutations were in giving us the food we eat at the scale we eat it, and knowing that there’s more potential out there,” Lippman said. “The more we understand behind the scenes, the more we have a chance to tweak the system, or the engine, if you will, to make it work even better.”
Source: CNN Brasil
Charles Grill is a tech-savvy writer with over 3 years of experience in the field. He writes on a variety of technology-related topics and has a strong focus on the latest advancements in the industry. He is connected with several online news websites and is currently contributing to a technology-focused platform.
