The establishment of mutualistic or pathogenic associations usually involves partner recognition and requires a specific molecular crosstalk between the plant and the invading microorganism. By comparison, the associative symbiosis (cooperation) between crop plants and PGPR bacteria (plant growth-promoting rhizobacteria) are considered as "simple" interactions, involving low or no specific responses. AZORIZ project aims at characterizing the molecular basis of the specificity of associative sy mbiosis between Azospirillum lipoferum strains and their corresponding host rice culti var. With a simplified and checked system of inoculation, the following analyses were conducted seven days after inoculation : (i) the plant growth promoting effect of each strain on the two rice cultivars; (ii) the rice root colonization patterns; (iii) the metabolomic response of the host; (iv) the transcriptomic response of the plant; (v) the transcriptomic response of Azospirillum. The results obtained concerning the parameters of growth show a differential response of the plant according to the inoculated strain and indicate a stronger effect when a strain is tested on its cultivar of origin. Moreover, significant modifications of the secondary metabolism on both rice cultivars were shown in response to the inoculation, with higher effect for extracts from roots (by comparison to extracts from leaves).We provide the first results of the transcriptomic responses of both partners in order to identify the potential genetic determinants defining the specificity of interaction and to test at the whole genome scale the genes/TE interactions in response to these biotic interactions. (résumé d'auteur)