How Roses Got Their “Thorns” – 11/08/2024 – Science

There is no rose without thorns, as the old saying goes. But to botanists, there is no rose without thorns: the pointed structures on its stem are called acoli, and they are biologically different from the hard, woody thorns of other plants.

Thorns are a striking example of evolution repeating itself. Over the past 400 million years, plants have evolved 28 times. Roses grow “thorns” on their stems, while others grow them on their leaves or fruit.

new Studying This publication in Science on January 1 sheds some light on how plants evolved spines from scratch so many times: each species benefited from a single gene. The discovery opens up the possibility of modifying plants’ DNA to remove their spines, making it easier to grow some wild plants as crops.

Plant geneticist Zachary Lippman of Cold Spring Harbor Laboratory in the US became interested in thorns while studying a group of crops including potatoes, tomatoes and eggplants. Although this group is thornless, some of its wild relatives are covered in thorns.

He believed that early farmers must have removed the thorns from wild plants when they began using them for agriculture. He asked, “Who would want to grow eggplants that you can eat if they have thorns stabbing you all the time?”

The loss of spines led Lippman and his colleagues to wonder how spines evolved in the first place. They probably emerged in many plants as a defense against animals that might eat them. But they can also serve other purposes. Some plants use them to cling to surfaces as they climb. Some wild grasses use them to attach their seeds to the fur of passing animals.

Charles Darwin realized that the same trait can evolve multiple times throughout the history of life, a process known as convergence. For example, bats and birds both evolved wings for flight. But they followed different evolutionary paths to get to the same end: bat wings evolved as membranes that grew between their fingers, while bird wings are made of feathers.

To understand how plants converge on thorns, Lippman and his colleagues hybridized a domesticated eggplant variety with its prickly wild relative. Some of the hybrids had many thorns, while others had none.

By comparing the plant’s DNA, the scientists discovered that a specific variant of a gene called LOG is carried only by plants with thorns. Botanists have long known that these genes help produce a hormone that signals plant cells to grow. But in the wild eggplant, there’s a special version of it that allows thorns to grow.

Lipman did the same experiment with two other eggplant species, crossing them with their wild relatives. It was later found that one form of LOG was responsible for the spines in the wild plants.

“We found that it was the same gene that had accumulated mutations independently in all three lineages to cause these spikes to be lost,” Lipman said.

It may seem interesting that a mutation in the LOG gene can remove thorns without harming the eggplant as a whole. After all, these genes are known to be essential for the growth of all plants.

It turns out that plants have evolved multiple versions of the LOG gene over millions of years. Lippman and his colleagues hypothesize that one version of the gene evolved in the eggplant’s wild ancestors to produce spines, while the other versions continued their original function of helping plants grow.

He and his colleagues wondered whether LOG genes were important for spines in other plants, too. In dozens of species, they found evidence of the same connection. For example, blocking the LOG gene in roses interferes with the development of “spines.”

The new findings could help scientists turn wild plants into domesticated crops, according to Lipman. He and his colleagues tested the possibility in a wild Australian plant that normally has thorny fruits. After the researchers removed the LOG gene from its DNA, it became thornless.

The work showed that convergence could happen in a way Darwin didn’t anticipate, said evolutionary biologist Vivian Irish of Yale University, who was not involved in the new study. Every time spines appeared, plants didn’t evolve an entirely new way to make them. They just reused the same gene over and over again.

“In many cases, innovation may simply reflect the reuse of old genes in new ways,” Irish said.