Use of more appropriate promoters

Silencing phenomena may result from the introduction of transgenes expressed under the control of strong promoters. The most commonly used promoter has been the constitutive 35S-CaMV promoter which has been used to engineer herbicide- and pathogen-resistant plants. In many instances however, the efficient manipulation of other agronomically or commercially interesting traits would require the expression of the transgene in a predictable and suitable manner which, in turn, would avoid undesired genetic damage and unpredictable transgene expression. In this context, inducible promoters provide an ideal tool to express heterologous genes. However, use of these promoters is limited because the naturally occurring levels of signal molecules may vary according to the environmental and developmental factors. Furthermore, these signals generally alter the expression of many endogenous genes. To circumvent these problems, the production of synthetic promoters responding to chemical inducers would be of great value. [104]