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Apart from being a symbol of love and romance, roses are often known for their sharp spikes – prickles that extend from the stems to keep animals from trying to pick the buds.
They are not the only plant with this defense mechanism: Other flowers like spider flowers or brambles, the flowering bush responsible for raspberries and blackberries, have sharp points, as do certain crop plants like tomatoes, eggplants, barley and rice. .
But how could all these species, many of which have evolved separately over millions of years, share the same spiny feature? An international team of researchers discovered that the answer lies in their DNA, tracing the origin to a single ancient gene family responsible for the prickles in all these variations, according to a new study published Thursday in the journal Science.
The findings not only open the door for scientists trying to create prickle-free versions but also provide insight into the evolutionary history of a remarkably diverse plant genus, experts say.
The evolution of prickles
Contrary to pop culture references, roses do not have thorns, which are the sharp woody points of certain shrubs and trees, including honey locusts and citrus trees. Instead the flowers have prickles that form from the skin of the plant, similar to how hair grows.
Clams have been around for at least 400 million years, dating back to when ferns and their relatives appeared with some prickles on their stems. The trait has since popped up – and disappeared – at different points in evolutionary time, said study co-author Zachary Lippman, a plant biologist and professor of genetics at Cold Spring Harbor Laboratory on Long Island, New York.
One of the most diverse plant genera, called Solanum – including crops such as potatoes, tomatoes and eggplant – was first found prickles 6 million years ago. Today, the genus has more than 1,000 species that can be seen around the world, with about 400 of those called “spiny solanum” for their prickles, according to the University of Utah.
When a common trait, such as prickles, appears independently across different lineages and species, this is called convergent evolution, and it occurs when species similarly adapt to certain environmental requirements. Wings are another example of a feature 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 the wing structure, said Lippman, who is also an investigator of the Howard Hughes Medical Institute. .
Thorns and thorns are an evolutionary defense against herbivores – animals that eat plants – and can also help with growth, plant competition and water retention, according to the study. It is not known exactly what caused ferns and other unrelated plants to grow the crows. Now, the study’s authors have discovered that an ancient gene family called Lonely Guy, or LOG, has been a gatekeeper for the trait, turning it on and off in different species over millions of years.
Genes lonely guy
By removing prickles from different species, including roses and eggplants, the authors found that the LOG gene was responsible for the prickles in about 20 types of plants studied. LOG-related genes are found in all plants, even going back to mosses, which are considered the first dry land plants, Lippman said. The genes are responsible for activating a hormone called cytokinin that is important for basic plant functions at the cellular level, including cell division and expansion, which affects the plant’s growth.
“It’s not that there was one common ancestor that had prickles, and then it radiated over 400 million years to all these others, and then they were lost to time. In fact, it appears that they appear to be readily available in different lineages,” Lippman said. “Now, the question is, how often has evolution converged, not just the trait we see, but the genes behind the trait?”
He added, “Our study, I think, is probably the first to really show the power of those tools (genetic and genome sequencing) to span such a wide evolutionary distance to address this very classic question to undergo convergent evolution in the evolution of plant or animal organisms. .”
The discovery provides a valuable tool for researchers exploring the degree of defense the crows provide against herbivores. Assessing this level of protection has previously been challenging as removing plants by hand from already grown plants – to test if they are more vulnerable without them – risks damaging the tissue and potentially health endanger plants, said Tyler Coverdale, assistant professor of biological sciences at. The University of Notre Dame was not part of the new study.
“By breaking out prickles with targeted genetic mutations, we can more fully understand the ecological role of physical plant defenses,” Coverdale said in an email. “Prickles are a key evolutionary development that allows plants to resist herbivory, which is why many of the spiny Solanum are found in areas with historically high herbivory diversity. Without this key innovation, Solanum may have been much more restricted in range and diversity.”
To genetically remove prickles
Before this discovery, another method of removing prickles from plants was to try to cross-breed the plant with another variety that naturally lost its prickles, Lippman said, which is why some species of roses are without the prickles. spikes today.
But now that the gene responsible for the prickles has been identified, scientists can remove the prickles using genome editing techniques such as CRISPR, a method scientists use to modify living organisms with DNA. Targeted gene editing can easily create more variation and has less impact on the plant’s growth and fruit production, Coverdale said.
“Not only does this study tell us more about the evolution of prickles specifically, it also gives us insight into the mechanisms of how to engineer plant developmental pathways for agricultural improvement,” said Vivian Irish, a plant biologist and professor in the Yale University Department. of molecular, cellular and developmental biology. Irish was not part of the new study but she was the senior author of a study in 2020 that discovered thorns growing on plants through stem cell activity.
“(LOG genes) have been repeatedly co-selected (biological change in trait function) in different plant species to form prickles, and also repeatedly lost in lineages where prickles have been lost. … (c)selection may occur at many different levels as a rule of nature, and innovation may in many cases represent the reuse of old genes in new ways,” she said in an email.
For agricultural purposes, the risk may involve making the harvest easier and paving the way for lesser-known produce to get into grocery stores.
An example the authors use is desert raisins, which are berries grown on thorny bushes native to Australia. With the prickles removed, the berry could be harvested much more easily and would be more similar to common grocery store berries like blueberries and strawberries, Lippman said.
“It’s really about knowing more … and understanding how important mutations were to give us the food we eat at the scale we do, and knowing that there are more possibilities,” Lippman said. “The more we understand under the hood, the more opportunity we have to change the system, or the engine, if you like, to make it even better.”
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