Why do roses have thorns?

Thorns, mistakenly referred to as "thorns" for roses, have appeared in various plant varieties over hundreds of millions of years of evolution.

An international research consortium, led by Cold Spring Harbor Laboratory in the United States and involving INRAE, has discovered the gene responsible for the presence of thorns in different plant genera, including roses. These findings, published on August 1st in the journal Science, reveal the existence of a common genetic program responsible for thorns.


Rose bushes do not actually have thorns but prickles, which are lateral outgrowths of the epidermis, also found in plants like eggplants. Unlike thorns, which are modified stems or leaves, prickles can be detached without tearing the plant fibers.

Over 400 million years of evolution, many distant plant families have convergently developed prickles. These outgrowths offer numerous advantages for these plants as they help deter herbivores, retain and absorb atmospheric water, and support the growth of climbing plants.

In this context, a consortium of scientists focused on the origin of prickles in different plant families and genera, such as the genus Solanum (which includes eggplants, potatoes, and tomatoes) and the genus Rosa, which was particularly studied by INRAE scientists.

The researchers used a combination of genetic approaches, including the creation of a genetic map by crossing different species of eggplants, to pinpoint the location of the gene controlling prickle development, which had never been identified before.

Through their analyses, they discovered that the LOG gene is the determinant in controlling prickle development. This gene is involved in the synthesis of cytokinin, a vital plant hormone for cell proliferation and plant development. Researchers then identified this gene within the genome of other species, including roses. Altering or removing the gene, causing a loss of prickles, confirmed its role in the development of these outgrowths.

These findings demonstrate the existence of a common genetic program, responsible for a widespread and recurring plant morphological innovation, prickles, throughout evolution. They also open the possibility of understanding a developmental mechanism at the root of an adaptive evolution shared among several plant species.

Reference:
Satterlee J.W., Alonso D., Gramazio P. et al. (2024). Convergent evolution of plant prickles by repeated gene co-option over deep time.
Science, DOI: https://doi.org/10.1126/science.ado1663