A fusion genetic strategy was used to identify gibberellin (GA) signaling mutants in transgenic Arabidopsis expressing the beta-glucuronidase (GUS) and firefly luciferase (LUC) reporter genes under control of the GA-responsive GASA1 promoter. Initial analyses determined the spatial and temporal patterns of reporter expression, and showed that reporter induction by GA was antagonized by ABA. gamma-Irradiated M2 progeny with altered reporter activities were identified by LUC bioimaging followed by GUS assays and northern hybridization of the endogenous GASA1 mRNA. Genetic analysis showed that three mutants, which overexpressed both reporters and endogenous GASA1, were caused by recessive (goe1 and goe2, for GASA over-expressed) and semi-dominant (goe3) mutations at different loci. These mutants are altered in their sensitivity to GA and the GA biosynthetic inhibitor paclobutrazol, and in the expression of several GA signaling related genes.