The study investigates the role of symbiotic fungal endophytes in conferring stress tolerance to plants from different habitats. Native grass species from coastal and geothermal habitats require symbiotic fungal endophytes for salt and heat tolerance, respectively. The same fungal species isolated from plants in habitats devoid of stress did not confer these stress tolerances. Agricultural crop endophytes conferred disease resistance but not salt or heat tolerance. The authors define habitat-specific, symbiotically conferred stress tolerance as habitat-adapted symbiosis and hypothesize that it is responsible for the establishment of plants in high-stress environments. The endophytes colonized tomato and rice plants, conferring disease, salt, and heat tolerance, respectively, and also conferred drought tolerance regardless of the habitat of origin. Abiotic stress tolerance correlated with decreased water consumption or reactive oxygen species (ROS) sensitivity/generation but not increased osmolyte production. The ability of fungal endophytes to confer stress tolerance to plants may provide a novel strategy for mitigating the impacts of global climate change on agricultural and native plant communities.The study investigates the role of symbiotic fungal endophytes in conferring stress tolerance to plants from different habitats. Native grass species from coastal and geothermal habitats require symbiotic fungal endophytes for salt and heat tolerance, respectively. The same fungal species isolated from plants in habitats devoid of stress did not confer these stress tolerances. Agricultural crop endophytes conferred disease resistance but not salt or heat tolerance. The authors define habitat-specific, symbiotically conferred stress tolerance as habitat-adapted symbiosis and hypothesize that it is responsible for the establishment of plants in high-stress environments. The endophytes colonized tomato and rice plants, conferring disease, salt, and heat tolerance, respectively, and also conferred drought tolerance regardless of the habitat of origin. Abiotic stress tolerance correlated with decreased water consumption or reactive oxygen species (ROS) sensitivity/generation but not increased osmolyte production. The ability of fungal endophytes to confer stress tolerance to plants may provide a novel strategy for mitigating the impacts of global climate change on agricultural and native plant communities.