Regulation of a modified CaMV 35S promoter by the Tn10-encoded Tet repressor in transgenic tobacco.

We have investigated the use of the Tn10-encoded tet repressor-operator system to regulate the expression of a suitably engineered cauliflower mosaic virus (CaMV) 35S promoter in transgenic tobacco plants. First, a transgenic plant was generated which constitutively synthesizes 600,000 Tet repressor monomers per cell. In a second transformation step, the beta-glucuronidase (gus) gene under the control of a modified CaMV 35S promoter, containing two tet operators, was stably integrated into the plant genome of a tetR+ plant. Expression of the gus gene is repressed 5-fold, if the operators are located flanking the TATA box, and 50- to 80-fold when both operators are positioned downstream of the TATA box. This indicates that Tet repressor-operator complexes can form on plant chromosomes and interfere with transcription. Maximal induction is achieved after 0.5 h upon application of only 0.1 mg/l tetracycline. This fast and efficient induction makes the system useful for specifically inducing expression of transferred genes at different stages of plant development.