🌱 How plants learned to protect themselves from UV rays

Sunlight provides the energy needed for photosynthesis and growth, but it also exposes plants to harmful ultraviolet-B (UV-B) radiation. Plants must therefore strike a delicate balance between growth and protection.

By studying Marchantia polymorpha, a plant similar to the first land plants, an international team led by scientists from the University of Geneva (UNIGE) sheds light on the evolution of fundamental UV-B perception mechanisms and plant adaptation strategies to light stress.


As climate change alters exposure conditions to solar radiation, these results, published in the journal Plant Physiology, provide valuable insights.

Essential for photosynthesis, which allows plants to produce organic molecules (sugars) and induce oxygen production, light can also have harmful effects on them. Just as in humans, UV-B can cause damage to DNA or cell membranes, and also impair the mechanisms responsible for photosynthesis.

Over the course of evolution, plants have developed a system based on a key photoreceptor, UVR8, to protect themselves from UV-B rays. When this sensor absorbs them, it triggers a cascade of molecular reactions that alter the expression of many genes and the production of molecules involved in protection and acclimation.

In modern flowering plants, especially thale cress, this signaling pathway involves several regulatory proteins that control the expression of many genes related to growth and tolerance to light stress. But how did this defense mechanism develop over evolution?

The laboratory of Roman Ulm, a full professor at the Department of Plant Sciences in the Section of Biology at UNIGE's Faculty of Science, focused on the common liverwort (Marchantia polymorpha), a species from a lineage that appeared more than 400 million years ago, when the first plants began to colonize dry land.

While the fundamental 'building blocks' of the system were already in place very early in plant evolution, their organization and regulation have been progressively remodeled.

An ancestral defense system

The scientists show that the fundamental activation mechanism of UVR8 is remarkably conserved between Marchantia and modern flowering plants. This ancestral core notably includes the activation of the UVR8 photoreceptor by UV-B as well as its deactivation mechanism.

However, the study also highlights an important evolution of interactions between these components. "Our work shows that in Marchantia polymorpha, certain regulatory proteins play different roles than those observed in more recent plants.

For example, the SPA protein, which acts with the central regulator COP1 in controlling plant growth in thale cress, plays a very different role in Marchantia. While it strongly participates in the regulation of development in flowering plants, its influence appears much more limited in this ancestral liverwort. Marchantia mutants lacking SPA even show increased tolerance to UV-B, suggesting that this protein acts here as a brake on the protective response," explain Yuanke Liang and Roman Podolec, postdoctoral researchers in Roman Ulm's laboratory and co-first authors of the study.

"Our results suggest that while the fundamental 'building blocks' of the system were already in place very early in plant evolution, their organization and regulation have been progressively remodeled," summarizes Roman Ulm.

By providing new insights into the evolution of light adaptation mechanisms, this study contributes to a better understanding of plant resilience to environmental stress. In the context of climate change, this knowledge could help anticipate plant responses to changing light conditions.