Ancient land plant discovery reveals origins of a 400-million-year-old UV-B protection system that helped plants conquer Earth

For over 400 million years, plants have been able to utilise an amazing defensive strategy in order to shield themselves from damaging ultraviolet-B (UV-B) radiation emanating from the sun. The latest research conducted by studying Marchantia polymorpha, a liverwort that is closely related to the first plants known to have colonised Earth, has helped us understand the evolution of this survival technique throughout time. This research has provided us with a unique insight into the molecular evolution that facilitated the move of plants from aquatic to terrestrial habitats. It is fascinating to learn that some of the 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 preserved for 400 million years

Scientists at the University of Geneva explored Marchantia polymorpha, which represents an ancestral branch of bryophytes appearing during 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 paid attention to a receptor named UVR8 that is responsible for the detection of UV-B rays and the induction of defence reactions in plants. In particular, according to the scientists, the basic mechanisms of activation and deactivation of the protein UVR8 have been preserved in plants for hundreds of millions of years of evolution.

According to lead researcher Roman Ulm:

"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 the regulation of growth under solar irradiation.

Why UV-B protection was crucial for the first plants on land

The shift from aquatic organisms to terrestrial organisms led to a 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.

It is well established in earlier research that plants developed a unique mechanism through which they detect UV rays and protect themselves from potential harm caused by the harmful radiation before any kind of damage occurs. The scientists discovered that it was due to a particular receptor known as UVR8.

As a botanist, Martin Balcerowicz commented:

"In adapting to terrestrial life, plants had to face huge changes in the levels of UV-B radiation."
This ability to detect radiation enabled early plants to colonise Earth successfully, leading to the formation of forests and ecosystems.

What the discovery reveals about plant evolution and climate resilience

However, the experiments showed not only the conservation of the signalling core of the UVR8 response pathway but also the evolutionary modifications in regulatory proteins that determine plant responses to UV stress.

Firstly, the protein SPA shows certain differences in its role within the signalling pathways between Marchantia polymorpha and higher plants. It seems to play a role as an inhibitor of stress response mechanisms in liverworts, thus providing the idea of how the signalling cascades evolved in the course of plant evolution.

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.

It should be noted that the growing global changes in environmental conditions make knowledge about plant evolution and adaptations extremely useful.