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Legume plants establish symbiosis with rhizobia to obtain nitrogen from atmosphere by nitrogen-fixing ability of endosymbiotic rhizobia. Most terrestrial plants including legumes make symbiosis with arbuscular mycorrhizal (AM) fungi, which help the host plants in nutrient uptake, especially in phosphate uptake through the hyphae developed in soil. These two symbiotic systems are thought to be highly valuable for establishing sustainable agriculture. In both symbioses, microsymbionts endow these valuable functions under the strict control by the host plants. Genetic defects in the host plant mechanisms required for these functions cause incompetence in symbiotic association itself. Model legumes have allowed us to identify host plant genes essential for those functional symbioses. Here we describe recent advances in understanding host plant gene functions involved in symbiotic nitrogen fixation and mycorrhizal symbiosis.