Dynamic DNA methylation in Posidonia oceanica under multiple stresses

In recent years, the understanding of epigenetic regulation responses to environmental stressors is gaining attention especially for marine organisms. Seagrasses are particularly susceptible to environmental changes such as the intensification of warming and eutrophication events and the occurrence of rapid environmental changes is forcing native populations to respond quickly. Recent studies performed on terrestrial plants have shown that new phenotypes can be generated through epigenetic modifications contributing to fast plant responses. Here we explore, for the first time in seagrasses, the dynamisms of 5mC-methylation patterns in Posidonia oceanica shoots collected from environmental sites with different nutrient conditions. For this purpose, we exposed P. oceanica plants in a common garden experiment to nutrient enrichment, temperature increase and their combination to evaluate the dynamic of DNA methylation patterns during the exposure to multiple stressors. Since in plants the modulation of epigenetic responses to environmental conditions represent a potential and robust mechanism to regulate gene expression network, we also aim to analyze expression profiles of epigenetic related genes and stress responsive genes in both plants along the experiment to understand how DNA methylation patterns evolve under multiple stressors and their potential role in driving P. oceanica responses. Results showed that the methylation levels decreased along the experiment with higher percentages measured at the beginning of the initial exposure to stresses. Nutrients highly affected DNA methylation level in both plants suggesting that the presence of only nutrients is considered as the main stressor to trigger epigenetic responses. Local environment conditions seemed to influence methylation levels and plants experiencing chronic exposure to eutrophication in natural environments appeared less methylated than nutrient limited plants. These findings give prominence to the potential role of epigenetic mechanisms in driving rapid seagrass responses to future scenarios.