Regulation of gene expression by small molecules in rice

A system for the regulation of gene expression by small molecules in transgenic rice was developed. This gene switch system consists of two components: (1) a hybrid chemically activated transcription factor, and (2) a synthetic target promoter. The two elements were transformed into rice suspension cells and transgenic plants were regenerated. A luciferase reporter under control of the gene switch system displayed as high as 10 000-fold inducibility following exposure to the small molecule ligand. The dose-response and induction time-course were determined. Regulated luciferase activity in activated plants decreased one day following removal of ligand and could be reactivated multiple times without apparent cosuppression. Analysis of luciferase activity following ligand application to media surrounding the roots suggests that ligand can be absorbed and transported systemically. In contrast, reporter activation was limited to a small area when ligand was applied directly to the leaf surface. The described gene switch system represents an important tool for situations requiring conditional gene expression in a monocot species.