Drought, heat, and other environmental stresses associated with global warming are major limiting factors for plant productivity. Concurrently, a continuous increase in crop yields is essential to keep pace with the growing world population and achieve food security for future generation - despite restricted cultivable land and other limiting natural resources. To this end, it is imperative to explore and develop new sustainable crop improvement strategies. Modern breeding methods have contributed substantially to improving agronomic traits; yet, extensive selection has resulted in losing genetic diversity in elite crop varieties. Moreover, new breeding technologies involving genetic modification face legislative barriers and consumer reservations. With regards to these challenges, natural and induced epigenetic variation constitutes an alternative source of trait modification, but its usefulness in agriculture remains unclear.
Plant acclimation to recurring stress involves epigenetic changes mediated by methylation of DNA and histones, which are the main constituents of chromatin. It is known that environmental stress causes changes in DNA and histone methylation but the underlying mechanisms and biological functions are still poorly understood. Therefore, this project focused on the molecular interactions between stress-related metabolic changes and chromatin methylation in the model plant Arabidopsis to gain new insights into plant acclimation mechanisms and how they can be used for crop production under challenging environmental conditions.
DNA and histone methylation are catalyzed by distinct methyltransferases, which require the cofactor S-adenosylmethionine (SAM) as methyl donor. During methylation, SAM is converted to S-adenosylhomocysteine (SAH), which in turn is a competitive inhibitor of SAM-dependent methyltransferases. SAM production and SAH degradation are integral parts of the methionine cycle, which depends on methyl supply by folate-mediated one-carbon (C1) metabolism. Accordingly, changes in C1 metabolism can affect DNA and histone methylation patterns and are associated with diseases and developmental defects. We have previously shown that MTHFD1, a central enzyme in folate metabolism, is required for maintaining proper DNA and histone H3K9 methylation. Here, we further investigated the molecular function of MTHFD1 to understand its role in DNA and histone methylation. Thereby, we particularly focused on the involvement of MTHFD1 in redox homeostasis.
In conclusion, we observed that MTHFD1 plays an important role in stabilizing DNA methylation patterns against environmental stress. Accordingly, mthfd1 mutants showed increased dynamics of genome-wide DNA methylation, whereas leave tissue DNA methylation patterns in wild type plants were largely robust against exposure to reactive oxygen species. In addition, we observed impaired redox homeostasis and increased levels of light- and UV-induced reactive oxygen species in leaf tissue of mthfd1 mutants, indicating that MTHFD1 is involved in antioxidant defence. Our results provide new insights into the mechanisms of DNA methylation dynamics during stress responses and contribute to our understanding of the environmental impact on epigenetic changes in plants.
