Résumé
Plant response to abiotic stress is a main challenge in a context of global climate change. The understanding of physiological as well as genetic/molecular processes controlling plant‘s response to abiotic stress will help to improve plant breeding. Recently, epigenetic mechanisms such as DNA methylation have been proposed to participate to 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 perennial plants such as trees that are exposed to repeated fluctuations of their living conditions. In order to assess this question in a perennial plant, we analysed poplar (Populus tremula × Populus alba) RNAi lines inhibited for the DECREASED DNA METHYLATION 1 gene (DDM1, involved in the maintenance of DNA methylation profile). A droughtrewateing experiment was conducted to evaluate the role of DNA methylation in tree phenotypic plasticity. Phenotypic characterization deals with data related to growth, photosynthetic capacities, water-use efficiency, xylem vulnerability to cavitation, xylem anatomy, phytohormones dosage, wood density and Mid Infra-Red spectroscopy (MIRS). Then, epigenomics studies in relation to DNA methylation have been realized: global DNA methylation, Whole Genomic Bisulfite Sequencing (WGBS) and Transposable Elements analyses. Bioinformatics analyses are in progress to identify ‘Differentially Methylated Regions’ in relation to phenotypic plasticity and the role of DNA methylation in memorizing environmental stress.