Comparing constitutive promoters using CAT activity in transgenic tobacco plants

The effectiveness of different promoters for use in transgenic tobacco was compared using a reporter gene expressing chloramphenicol acetyl transferase (CAT). Plasmids with CAT gene controlled by cauliflower mosaic virus 35S (CaMV 35S), rice actin1 (Ract1) and tobacco polyubiquitin (Tubi.u4) promoters were delivered into tobacco plants by Agrobacterium-mediated transformation. The Ract1 promoter, previously shown to be a strong promoter in rice and other monocots, failed to promote strong expression in tobacco. CAT expression was greatest from the vector carrying Tubi.u4 with a 5'UTR and leader intron without a ubiquitin monomer. In transgenic plants harboring the Tubi.u4 promoter, CAT expression was approximately twice that of the CaMV 35S promoter. Our results suggest that foreign genes under the control of a ubiquitin promoter devoid of monomer will be useful for high-level gene expression in tobacco.