A novel stable transgenic plant expression system was developed using elements of the replication machinery of Bean Yellow Dwarf Virus (BeYDV). The system contains two transgenes: 1) The BeYDV replicon vector with an expression cassette flanked by cis-acting DNA elements of BeYDV, and 2) The viral replication initiator protein (Rep) controlled by an alcohol-inducible promoter. When Rep expression was triggered by treatment with ethanol, it induced release of the BeYDV replicon from stably integrated T-DNA and episomal replication to high copy number. Replicon amplification resulted in substantially increased transgene mRNA levels (up to 80-fold) and translation products (up to 10-fold) after induction of Rep expression by ethanol treatment in tobacco NT1 cells and leaves of whole potato plants. Thus, the BeYDV stable transformant replicon system is a powerful tool for plant-based production of recombinant proteins. (c) 2005 Wiley Periodicals, Inc.