P. indica is a beneficial root endophytic fungus which promotes plant growth and induces resistance against abiotic and biotic stress. The wide host range also provides the possibility for investigating the role of multiple functions in symbiosis. In my research, the following 3 aspects were investigated. 1. The role of P. indica in Chinese cabbage/P. indica interaction under drought stress P. indica strongly colonizes the roots of Chinese cabbage and promotes lateral root development. Under drought stress, activities of antioxidants were highly upregulated within 24 h in the leaves of fungal-colonized plants. P. indica also prevents the degradation of chlorophyll and thylakoid proteins. MDA accumulates less in the drought-exposed leaves of colonized plants. In addition, the drought-related genes were upregulated and the amount of the CAS protein was strongly increased in the leaves of the colonized plant. The drought stress was reliefed in the presence of P. indica. 2. The role of P. indica in Arabidopsis/P. indica interaction under V. dahliae challenge P. indica reduces V. dahliae-mediated disease development and inhibits growth of V. dahliae on agar plates as well as in seedlings. The P. indica-pretreated plants perform better after V. dahliae infection, do not activate stress hormones and defense genes and the number of microsclerotia is dramatically reduced. In addition, the pathogenicity of V. dahliae is associated with an increase in [Ca2+]cyt induced by an exudated compound of the pathogen in Arabidopsis roots and requires the ethylene-activated transcription factor EIN3. 3. Auxin plays a more important role in the interaction of P. indica with Chinese cabbage than with Arabidopsis Both Chinese cabbage and Arabidopsis do not require P. indica-derived auxin for the growth response. But the elevated auxin levels in Chinese cabbage suggest that the P. indica-induced growth promotion is strongly dependent on auxin.