For over 400 million years, plants have utilized an amazing defensive strategy to shield themselves from damaging ultraviolet-B (UV-B) radiation from the sun. The latest research, conducted by studying Marchantia polymorpha, a liverwort closely related to the first plants known to have colonized Earth, has helped scientists understand the evolution of this survival technique. This research provides unique insight into the molecular evolution that facilitated the move of plants from aquatic to terrestrial habitats. It is fascinating to learn that some components crucial for UV-B detection and protection have existed since the days when the first plants started living on Earth.
Scientists Uncover an Ancient UV-B Protection System
Scientists at the University of Geneva explored Marchantia polymorpha, which represents an ancestral branch of bryophytes appearing during the initial periods of plant adaptation to life on land. The investigation showed that key features of the UV-B sensing system have been preserved intact between primitive liverworts and flowering angiosperms. Specifically, the scientists focused on a receptor named UVR8, responsible for detecting UV-B rays and inducing defense reactions in plants. According to the scientists, the basic mechanisms of activation and deactivation of the UVR8 protein have been preserved in plants for hundreds of millions of years of evolution.
Lead researcher Roman Ulm stated: "According to our study, while the essential building blocks of the system appeared very early in evolution, their arrangement and regulation have undergone progressive modification." Thus, even ancient plants possessed quite advanced systems for regulating growth under solar irradiation.
Why UV-B Protection Was Crucial for the First Plants on Land
The shift from aquatic to terrestrial life led to much higher exposure of plants to ultraviolet light. The lack of protection from UV-B rays in terrestrial environments was not the same as in aquatic ones. Earlier research established that plants developed a unique mechanism to detect UV rays and protect themselves from potential harm before any damage occurs. This ability was due to the UVR8 receptor. Botanist Martin Balcerowicz commented: "In adapting to terrestrial life, plants had to face huge changes in the levels of UV-B radiation." This detection ability enabled early plants to colonize Earth successfully, leading to the formation of forests and ecosystems.
What the Discovery Reveals About Plant Evolution and Climate Resilience
The experiments showed not only the conservation of the signaling core of the UVR8 response pathway but also evolutionary modifications in regulatory proteins that determine plant responses to UV stress. For instance, the protein SPA shows certain differences in its role within the signaling pathways between Marchantia polymorpha and higher plants. It appears to act as an inhibitor of stress response mechanisms in liverworts, providing insight into how signaling cascades evolved over time. Therefore, it can be concluded that early land plants had already acquired the main elements necessary for effective UV resistance, and further evolution led to their improvement and expansion. Given growing global changes in environmental conditions, knowledge about plant evolution and adaptations becomes extremely useful.
