Ectomycorrhiza is a symbiosis between roots of woody plants and ectomycorrhizal fungi. Ectomycorrhiza can help plant roots with water and nutrient absorption, and increase plant resistance to environmental stress. The architecture and hydraulic conductivity of plant roots changed after ectomycorrhiza formed. Analyzing gene expression in plant roots induced by ectomycorrhizal fungi shows how ectomycorrhiza affects plant resistance to drought at molecular levels.