In temperate zones the global change will include a decrease of summer precipitations inducing longer and more severe drought episodes. Transcriptional regulation plays a major role in regulating many biological processes, we looked for gene expression networks related to drought stress. The final aim is to identify candidate genes for water deficit acclimation and/or adaptation in poplar, a model tree species. The transcriptome of two Populus deltoides x nigra genotypes of contrasted tolerance to water deficit (Carpaccio and Soligo) were analysed in young mature leaves, at various stages and intensities of stress. Four watering treatments were applied: control (CTL) watered to field capacity six-times a day; early response to water deficit (EAR): watering was stopped 30h before harvest; and acclimated response to mild (AMI) and to moderate (AMO) water deficit. The latter two stress levels were low enough so primary and secondary growth were reduced but not stopped. Mature leaves were harvested and their transcriptome analysed using wholegenome microarray (GeneChip Poplar Genome Array, Affymetrix). The physiological responses to water deficit confirmed the higher tolerance of the Carpaccio as compared to the Soligo genotype. On the other hand, the transcriptomic results show strong cultivar specificity in optimal watering conditions as well as in water deficit treatments. Analyses of the responses allowed us to confirm potential drought markers and to identify candidate genes for drought tolerance.