The Molecular Signature for Local Adaptation in the Seagrass Posidonia oceanica

In the last century, seagrass ecosystems have suffered a worldwide decline ascribed to multiple environmental stressors, among which the reduction of light available for the photosynthesis and the increase in temperature represent the strongest constraints for their growth and survival. Despite conservation, this decline is at present still continuing. In order to understand the genetic adaptive response to light and temperature in the seagrass Posidonia oceanica , two different strategies have been pursued: a genome scan approach along a latitudinal and a bathymetric gradient and a differential gene expression analysis along the bathymetric gradient, where light and temperature were the two main selective factors. For the genome scan approach 6 populations (Delimara - Malta, Lacco Ameno - Island of Ischia, Italy, Marettimo Island- Italy, Meloria - Italy, Piombino - Italy and Stareso - Corsica, France) were sampled along the bathymetric gradient at two different depths (-5m and -25m). The same populations were used for the latitudinal gradient analysis by grouping them on the basis of their geographic location (Southern group: Delimara, Lacco Ameno and Marettimo; Northern group: Meloria, Piombino and Stareso). No genes under selection were identified in the genome scan along the bathymetric gradient. Three putative genes under selection were identified in the genome scan along the latitudinal gradient and were involved in the photosynthesis and in the translation process. For assessing differential gene expression, a transcriptome sequencing of plants sampled at two different depths and different times of the day in the Stareso meadow was performed by RNAseq technology. The analysis highlighted the capability of plants living in shallow waters to cope with environmental stresses imposed by high light and high temperature. Transcriptome data generated from this study increased the resources available in P. oceanica and will be very useful for further investigations of the adaptation of in this plant.