Arbuscular mycorrhizal fungi (AMF) establish a symbiotic association with the roots of 80% of terrestrial plants and form complex tree-shaped feeding structures called arbuscules in colonized root cells. This association with AMF not only provides more efficient uptake of nutrients for the plant, but also confers protection against pathogens and increased tolerance to environmental stress such as salt stress [1]. Rice (Oryza sativa), the most salt-sensitive crop species amongst cereals, has a productivity strongly reduced around the world due to soil salinity/salinization and increased sea level (in deltas). High Na+ concentrations (salt stress conditions) impairs K+ uptake and inhibits many K+-activated enzymes. Rice exhibits molecular mechanisms to alleviate salt stress such as maintaining a high cellular K+/Na+ ratio, e.g. by a more efficient K+ uptake, which was recently shown to occur upon root/AMF interaction [2]. Knowledge on the role of root/AMF interaction on K+/Na+ transport upon salt stress is sparse [2, 3]. The aim of the research is to understand the mechanisms by which AMF improve plant K+ nutrition upon salt stress, taking Rhizophagus irregularis (model AMF)-rice interaction as a model. We will investigate the mechanisms by which AMF mediate K+ uptake and translocation towards root cells. Rice loss-of-function mutants for each of the three major K+ uptake systems of the plant, OsAKT1, OsHAK5 and OsHAK1, were inoculated with R. irregularis and submitted to salt stress, and their K+ contents and K+/Na+ ratios were monitored to identify key player(s) for AMF-mediated improved rice K+ nutrition and salt tolerance.