Abstract
Beneficial plant-microbe associations play significant roles in both natural and agricultural systems. For example, fungal end ophytes have profound impacts on growth and physiology of plants, which may be particularly important under conditions of stress. To study the impact of endophyte infection, we inoculated seedlings of Nicotiana benthamiana with two ascomycetous fungal endophytes, an isolate of Cladosporium cladosporioides and an unidentified ascomycete fungus. Endophyte colonisation caused significantly differential accumulation of 17-21 metabolites including sugars, sugar alcohols, amino acids and other metabolites at various stage s of plant growth and stress application. The water stress tolerance of fungus-inoculated plants was correlated with increases in plant biomass, relative water content, soluble sugar, soluble protein, proline content, increased activities of the antioxidant enzymes catalase, peroxidase and polyphenol oxidase, decreased production of reactive oxygen species, and decreased electrical conductivity. In addition, there was significant upregulation of several genes previously reported as drought-induced. The findings suggest a symbiotic relationship between these fungi and N. benthamiana plants, a species adapted to hot and unpredictable soil moisture conditions of northern Australia. Importantly, this work sheds light on the mechanisms underlying enhanced tolerance to water stress provided by fungal endophyte infection.