We demonstrate that native grass species from coastal and geothermal habitats require symbiotic
fungal endophytes for salt and heat tolerance, respectively. Symbiotically conferred stress tolerance
is a habitat-specific phenomenon with geothermal endophytes conferring heat but not salt
tolerance, and coastal endophytes conferring salt but not heat tolerance. The same fungal species
isolated from plants in habitats devoid of salt or heat stress did not confer these stress tolerances.
Moreover, fungal endophytes from agricultural crops conferred disease resistance and not salt or
heat tolerance. We define habitat-specific, symbiotically-conferred stress tolerance as habitatadapted
symbiosis and hypothesize that it is responsible for the establishment of plants in highstress
habitats. The agricultural, coastal and geothermal plant endophytes also colonized tomato
(a model eudicot) and conferred disease, salt and heat tolerance, respectively. In addition, the
coastal plant endophyte colonized rice (a model monocot) and conferred salt tolerance. These
endophytes have a broad host range encompassing both monocots and eudicots. Interestingly, the
endophytes also conferred drought tolerance to plants regardless of the habitat of origin. Abiotic
stress tolerance correlated either with a decrease in water consumption or reactive oxygen
sensitivity/generation but not to 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