Accumulation of trehalose increases soluble sugar contents in rice plants conferring tolerance to drought and salt stress

Trehalose is a nonreducing sugar composed of two glucose units linked in an alpha,alpha-1,1-glycosidic linkage. Present in a wide variety of organisms, this sugar may serve as a source of energy and carbon and as a protective molecule against abiotic stresses. In this study, trehalose-producing transgenic rice plants (Oryza sativa) expressing a bifunctional fusion enzyme TPSP (Ubi1:TPSP) were utilized to dissect the enigmatic role of trehalose in conferring stress tolerance to plants. Grown under normal conditions, the Ubi1:TPSP plants produced high amounts of soluble sugars (glucose, fructose and sucrose), ranging from 1.5- to 3.5-fold over NT controls. In the time course of drought treatment, the transcripts for the drought degradable-marker genes (RbcS, FBPase, and PBZ1) persisted for two more days in Ubi1:TPSP plants before being completely degraded relative to those in NT plants, confirming the tolerance of the transgenic plants to drought. This was further supported by a delayed increase in transcript levels of the stress-inducible genes SalT, Dip1, and Wsi18 during drought stress. Similarly, Ubi1:TPSP plants showed tolerance to salt levels of up to 150 mM NaCl, as evidenced by the seedling growth and the delayed decay in RbcS and delayed increase in SalT transcript levels. The growth of NT plants was found to be slightly affected by exogenous trehalose feeding, whereas Ubi:TPSP plants remained resistant, validating the protective role of internally produced trehalose. These results suggest that the elevated production of trehalose in rice, through TPSP overexpression, increases the soluble sugar contents and enhances tolerance to both drought and salt stress.