Specific induction of secondary product formation in transgenic plant cell cultures using an inducible promoter

This paper describes the artificial induction of secondary metabolite production in transgenic plant cell cultures using a recombinant, inducible plant promoter. The bacterial gene ubiC from Escherichia coli encodes the enzyme chorismate pyruvate lyase (CPL) which catalyses the conversion of chorismate to 4-hydroxybenzoate (4HB). This gene was fused to the tetracycline-inducible plant promoter Triple-Op. After transformation into Nicotiana tabacum W38 TET, transgenic cell cultures were established. Addition of chlorotetracycline to the medium led to specific induction of CPL activity. The optimal chlorotetracycline concentration was approximately 2 mg/l medium. Three to 5 h after induction, the ubiC mRNA concentration reached a maximum, while highest specific CPL activity was detected after 8 days. The artificial secondary metabolite 4HB was converted to glucosides, and their accumulation reached maximum levels after 5 weeks of subculture. The induction was reversible.