Plant scientist Dario Leister and his team are investigating how cyanobacteria adapt to rapidly changing light intensities. This could help optimize photosynthesis in crops.

Photosynthesis is one of the most complex processes in nature. However, plants use only a fraction of the available light spectrum and are highly sensitive to environmental stressors such as changing light intensities, heat and drought. As climate change intensifies these stresses, safeguarding crop productivity is becoming an increasingly urgent challenge. To better understand the process of photosynthesis and at the same time identify starting points for improving it, researchers led by LMU biologist Dario Leister study model organisms such as the cyanobacterium Synechocystis.

In a study now published in Nature Communications, the scientists stressed Synechocystis by subjecting it to fluctuations in light intensity. “These kinds of conditions, in which high and low light intensities alternate at intervals ranging from one to several minutes, disrupt the process of photosynthesis and damage the photosystems,” explains Leister, who is Chair of Plant Molecular Biology at the Faculty of Biology in Martinsried. To find out how the blue-green algae can adapt to these unfavorable light conditions, the team recreated an accelerated evolutionary process in the laboratory.

Over time, this approach produced Synechocystis strains capable of tolerating light fluctuations that would normally be lethal. Genetic analysis of these adapted strains revealed mutations that influence the activity and relative quantity of biomolecules that are vital for photosynthesis. These include the protein-pigment complexes photosystem I and II and the light-harvesting antenna complexes. These evolutionary adaptations enhanced the resilience of Synechocystis to extreme variations in light intensity.

Plants growing in agricultural fields face similar challenges. Outdoor light conditions change constantly due to cloud cover, shading, and weather fluctuations, forcing crops to continuously adjust their photosynthetic machinery. “Photosynthesis works most efficiently at fairly low light intensity, whereas excessive light reduces efficiency. When the light levels change too quickly, the regulatory mechanisms cannot respond fast enough, which reduces efficiency and so also reduces the yield,” explains Dario Leister.

The findings from Synechocystis may provide new strategies for improving the ability of crops to cope with fluctuating light conditions. “The next step is to transfer the approach we used in our current study to eukaryotic algae because they are evolutionary closer to crop plants.” The biologist hopes that this will allow him to move step by step from relatively simple single-celled organisms toward applications in crops.

The study is part of the “PhotoRedesign: Redesigning the Photosynthetic Light Reactions” project, which has been funded by an ERC Synergy Grant from the European Union. In this research project, scientists from LMU are exploring new approaches for improving plant photosynthesis, using single-cell organisms like Synechocystis as model organisms because of their short generation times and the ease with which they can be genetically manipulated.

Ultimately, the goal is to produce crops that can utilize a broader range of light wavelengths. “To achieve this, it is important that optimized plants are also more robust and better able to cope with the additional absorbed light energy,” says Leister. The current study is providing new potential starting points for intervening in the complex photosynthetic apparatus of crops: “Our improved Synechocystis substrains contain point mutations that can also be transferred to related organisms using gene editing. With current legislative developments in the EU, such modifications may no longer be classified as transgenic in the future. Moreover, this strategy more closely resembles natural evolutionary processes than approaches based on overexpressing individual genes, which is a method often used by other researchers.”