Ecdysone Receptor-Based Gene Switches for Applications in Plants

Abstract

The selective induction of transgene expression is typically accomplished through the use of a promoter whose transcriptional activity is determined by the presence or absence of a specific inducer. There are a number of circumstances in which it is advantageous to use an inducible gene regulation system to modulate the gene expression, most obvious being when introducing transgenes whose constitutive expression is detrimental or even lethal to the host plants. In this context, several attempts have been made to develop chemically-inducible gene expression systems to regulate the expression of transgenes in plants. The utility of such a system is determined mainly by there being an undetectable expression of the trans-gene prior to application of the inducer chemical and the induced gene expression levels should be comparable to or higher than a strong constitutive promoter such as the CaMV 35S promoter. In addition, the optimal chemical inducible system would employ an inexpensive and non-toxic inducer whose application can be fully controlled. The ecdysone receptor (EcR)-based gene switch is one of the most applicable gene regulation systems available since the chemical ligand required for its regulation is already registered for field use. Ligand-binding domains from different EcRs have been used to create EcR-based gene regulation systems for applications in plants. Among them, the Choristoneura fumiferana EcR (CfEcR)-based system, which responds exclusively to non-steroidal ecdysone agonist, such as methoxyfenozide, was demonstrated to induce greater levels of transgene expression than the CaMV 35S promoter. The present review will focus primarily on different EcR gene switches developed to date and the recent advancements made to improve the utility of EcR gene switch technology for applications in plants.