Photorespiration is a cellular conversion process in which plants release carbon dioxide and consume oxygen when exposed to light. Until now, it has been considered an especially wasteful by-product of photosynthesis. Yet according to the latest studies by researchers from Helmholtz Munich, the Technical University of Munich, and Heidelberg University, this process in fact plays an important role in the preservation of the plant epigenome, which controls which genes are turned on or off in response to environmental influences. The investigations show that photorespiration provides carbon atoms required for the environmentally induced modification of plant DNA.
In their experiments on thale cress, a model organism in plant biology, the researchers looked into possible connections between photorespiration, one-carbon metabolism (C1 metabolism), and what is known as DNA methylation. This epigenetic mechanism enables plants to adapt to their environment. Aided by enzymes, small methyl groups are attached to specific building blocks of plant DNA. As chemical markers, they ensure that the activity of certain genes is attenuated or turned off entirely. The methyl groups are created during C1 metabolism.
"The results of our research show that there is a metabolic connection between photorespiration and the epigenetic regulation of plants," states Prof. Dr Rüdiger Hell, who heads the "Molecular Biology of Plants" research group at the Centre for Organismal Studies of Heidelberg University. Together with Dr Markus Wirtz, who researches the physiological stress reactions of plants, he quantified the related key metabolites.
Using genome-wide analyses, the researchers furthermore investigated how heightened concentrations of carbon dioxide (CO2) affect the methylome – the full set of DNA methylations in a plant genome. CO2 suppresses photorespiration and therefore the production of C1 metabolites. Accordingly, the methylome of thale cress changed, especially when alternative sources of C1 were also limited.
Photorespiration is therefore not merely a wasteful by-product of photosynthesis, the researchers emphasize. As a supplier of C1 metabolites, it is rather an important mechanism in the epigenetic control of plants. "In combination, our research results allow for a better understanding of how rising CO2 concentrations and environmental changes can affect plant genome regulation. We can also infer potential new approaches for future strategies to optimize crops," stresses Dr Martin Groth, who directed the research work at Helmholtz Munich.
The European Union and the German Research Foundation provided funding for the research. The results were published in the journal Nature Plants.
