Tn10-encoded tet repressor can regulate an operator-containing plant promoter.

The Tn10-encoded tet repressor-operator system was used to regulate transcription from the cauliflower mosaic virus (CaMV) 35S promoter. Expression was monitored in a transient assay system by using electric field-mediated gene transfer ("electroporation") into tobacco protoplasts. The tet repressor, being expressed in the plant cells under the control of eukaryotic transcription signals, blocks transcription of a CaMV 35S promoter chloramphenicol acetyltransferase (cat) fusion gene when the two tet operators flank the "TATA" box. In the presence of the inducer tetracycline, expression is restored to full activity. Location of the operators 21 base pairs downstream of the transcription start site does not significantly affect transcription in the presence of the repressor. These experiments show that a prokaryotic regulatory protein can function in plant cells. The tet repressor-operator complex may be useful for specifically inducing transferred genes at different stages of plant development.