Expression of the Grifola frondosa Trehalose Synthase Gene and Improvement of Drought-Tolerance in Sugarcane (Saccharum officinarum L.) Study on Effects of Acetic Acid on Enzyme Production of the Recombinant Escherichia coli BL21 and Its Action Mechanism Transformation of Maize Immature Embryos with Trehalose Synthase Gene Genetic Transformation of Tobacco with the Trehalose Synthase Gene from Grifola frondosa Fr. Enhances the Resistance to Drought and Salt in Tobacco