A chemical inducible gene regulation system that specifically regulates transgene expression in response to an exogenous inducer at a particular stage of plant development or in a specific organ is very valuable when using transgenes whose constitutive over expression is detrimental or lethal to the plant. A number of chemical inducible gene regulation systems, or gene switches, have been developed based on a diverse collection of non-plant regulatory elements that respond to a variety of chemicals (Gatz et al.
In order to achieve an optimal expression of transgenes with minimum undesirable effects, it is highly desirable to regulate the expression of transgenes in a controllable fashion. Regulation of transgene expression is of particular importance in genetic engineering of plants. The new CfEcR two-hybrid gene switch that uses the RXR CH9 as a partner in inducing reporter gene expression provides an efficient, ligand-sensitive and tightly regulated gene switch for plants. In both transient expression studies and stable transformation experiments, the fold induction values obtained with the CH9 switch were several times higher than the values obtained with the other EcR switches containing LmRXR or HsRXR.
The performance of CH9 was further tested in corn and soybean protoplasts and the data obtained was compared with the other EcR switches that contained the wild-type LmRXR or HsRXR as EcR partners. The RXR chimera 9 (CH9) along with CfEcR, in a two-hybrid format gave the best results in terms of low-background expression levels in the absence of ligand and high-induced expression levels of the reporter gene in the presence of nanomolar concentrations of the methoxyfenozide ligand. To further improve the versatility of the two-hybrid EcR gene switch for wide spread use in plants, chimeras between Homo sapiens retinoid X receptor (HsRXR) and insect, Locusta migratoria RXR (LmRXR) were tested in tobacco protoplasts as partners with Choristoneura fumiferana EcR (CfEcR) in inducing expression of the luciferase reporter gene. Recent development of a two-hybrid ecdysone receptor (EcR) gene regulation system has solved some of the drawbacks that were associated with the monopartate gene switch. Chemical inducible gene regulation systems provide essential tools for the precise regulation of transgene expression in plants and animals.
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