This chapter describes a method for rapid gene expression assays in Arabidopsis. Three distinct plasmids are codelivered into leaves by microparticle bombarment. The first one carries a transacting factor gene driven by the cauliflower mosaic virus (CaMV) 35S promoter. The second plasmid includes a reporter luciferase (LUC) gene transcribed from a promoter containing the TF binding site(s). The third plasmid contains a reference beta-glucuronidase (GUS) gene transcribed from the 35S-CaMV promoter, which is used to normalize data derived from independent experiments. This method could be applied to study systematically the functional properties of Arabidopsis transcription factors as well as to identify promoters and control region(s) regulated by specific transcription factors.