Transcriptional responses of Posidonia oceanica under multiple stresses: the influence of the native environment

Seagrasses are particularly susceptible to environmental changes such as the intensification of warming and eutrophication events. The occurrence of rapid environmental changes are threating natural populations. Posidonia oceanica is an endemic Mediterranean species and ranks amongst the slowest- growing and longest-lived plants on earth. Recent evidence revealed that P. oceanica plants distributed along bathymetric or latitudinal gradients show different transcriptomic responses to common stress, suggesting a crucial role of pre- adaptation to local environmental conditions in driving response to stress. Here we aimed to analyze the physiological and transcriptional responses of P. oceanica plants with different life histories to multiple stresses. Methods P. oceanica shoots collected from sites with different nutrient conditions (Eu plants = Eutrophic plants; Ol Plants = Oligotrophic plants) were exposed in a common garden experiment to nutrient enrichment, temperature increase and their combination. Leaf tissue was collected after two weeks of exposure to stressed conditions to assess the physiological status of plants and to analyze gene expression profiles, applying the TAG sequencing technique. Results Plants showed different transcriptional profiles against the same stress conditions. Differentially expressed genes varied among plants, with a higher genes activation in plants growing in a more stressed environment, in respect to plants growing in a pristine environment. The effect of temperature at physiological level was lower in comparison to nutrients and the analysis, as confirmed by gene expression results. An interesting expression pattern of methylation processes was observed, including a large number of genes related to histone modifications, supporting their role in modulation and control of gene expression. Conclusion The different life history of P. oceanica plants is crucial to understand future persistence of this species under rapid environmental changes. Local environmental conditions seem to modify plant responses to multiple stresses through transcriptional regulation, which could have an epigenetic basis.