Global climate changes in progress will impact tree productivity in the northern hemisphere. The understanding of physiological as well as genetic/molecular processes controlling plants response to abiotic stress will help to improve plant breeding. Recently, epigenetic mechanisms such as DNA methylation have been shown to participate to the control of plant development and their adaptation to environment through modifications of chromatin compaction and gene expression profiles. Phenotypic plasticity defines as the different phenotypes for a given genotype in distinct environments is a key process for plant to adapt to their changing environment. This is particularly relevant for perennialplants such as trees that are exposed to repeated fluctuations of their living conditions. In this context, drought is a significant threat to forest health and agro-ecosystem productivity. With the availability of its genome and its important natural genetic and phenotypic variations, Populus became a model tree.The aim of our project is to develop an integrative approach to identify ecophysiological and molecular bases, particularly DNA methylation, involved in phenotypic plasticity. Contrary to animals, plants exhibit a continuous development and their germline arise from very specific somatic tissue: the shoot apical meristem. We focus our effort to the study the role of DNA methylation in shoot apical meristem using various epigenomic approaches (MeDIP-SEQ, MeDIP-CHIP, WGBS) in parallel to transcriptomics and phenotyping. Our experimental designs include collection of genotypes and are established in controlled conditions such as in greenhouse and nursery as well as in field plantations. We have also characterized the first hypomethylated tree (DDM1-RNAi poplars) in different environments.Altogether, our results demonstrate the role of DNA methylation in memorizing environmental influence and identify the corresponding genes network in relation to phenotypic plasticity.