Melampsora larici-populina is a biotrophic fungus that infects poplar and causes the foliar rust disease, leading to severe damages in plantations. A major aim of the Tree- Microbe Interactions department is to characterize molecular determinants of the pathosystem. During this thesis, four research projects were achieved through post-genomic approaches. First, transcriptome analysis of the early interaction between poplar and M. larici-populina revealed a fungal-induced host sulfate transporter (chapter II). Secondly, the phylogenomic analysis of the thaumatin-like protein (TLP) family uncovered some clades specifically associated with stress responses in poplar (chapterIII). Thirdly, the gene encoding the small secreted protein of unknown function Risp is strongly induced during poplar defense reponses and has no homolog in other plants. The recombinant protein is intrinsically disordered and presents a dual activity as an antifungal protein against M. larici-populina and as an endogenous elicitor of defense responses in poplar (chapter IV and V). The combination of both properties in a single protein has never been reported in plants. Finally, M. larici-populina MlpP4.1 and MlpH1.1 genes encode cysteine-rich small-secreted proteins of unknown fonction, considered as candidate effectors (chapter VI). MlpP4.1 and MlpH1.1 expression is strongly induced during poplar leaf colonization, and virulence activities were observed in Arabidopsis thaliana. Biochemical and structural analyses of recombinant proteins are ongoing and already revealed the strong stability of MlpP4.1, likely due to the presence of several disulfide bridges. Several plant partners of the recombinant proteins were identified and have allowed for setting hypotheses about their role