The project aimed at making progress in the knowledge of the iron-mediated interactions between pea and fluorescent pseudomonads in order to promote the iron-nutrition and health of the host-plant. A bibliographical study was conducted to draw up the state of the art concerning the influence of rhizosphere microorganisms on plant iron status (Chapter 1).Pisum sativum has been chosen as an agronomic model-plant because of its high potential in agroecology and in Human nutrition related to its ability to fix atmospheric nitrogen and to the high amino-acids content of its seeds. However, this species suffers from a high susceptibility to iron deficiency as expressed by the well-known chlorosis symptom. The goal is to value pseudomonad’s siderophores through the promotion of pea iron-nutrition and health.The strategy used consisted in evaluating (i) the influence of two pea cultivars, tolerant (T) and susceptible (S) to iron chlorosis, on the diversity of fluorescent pseudomonads and of their siderophores (Chapter 2), and in return (ii) the variability of the beneficial effects of the siderophores according to their diversity at the level of the organism, and at the cellular and molecular levels. Bacteria, and siderophores representative of the described diversity, have been tested for (i) their antagonistic potential against a phytopathogen oomycete, Aphanomyces euteiches (Chapter 2), and (ii) their effects on the plant iron content and ionome (Chapter 3). Mechanisms involved in the beneficial effects, with a specific focus on the impact of the model-siderophores on iron homeostasis and regulation of the growth/defense balance, have been studied by analyzing (i) siderophore transport in planta of a model-siderophore at the cellular level (Chapter 4), and (ii) transcripts of genes involved in iron acquisition, homeostasis, regulation of the growth/defense balance and plant defense response, at the molecular level.Finally, the implications of these findings are discussed in a conclusive part.