Controlled gene expression in plants

This invention relates to the control of gene expression in plants using either a chimeric transcriptional activator protein system, or a system based on suppressor tRNAs. The chimeric transactivating proteins of the invention offer a variety of advantages, including the specific controlled activation of expression of genes engineered to comprise transactivator-responsive elements, thereby achieving exceptionally high levels of gene expression. In particular, the transactivator proteins of the invention comprise a DNA-binding portion of the prokaryotic Lac repressor operatively linked to a polypeptide which directly or indirectly activates transcription in eukaryotic cells. Further, the transactivation system comprises DNA molecules containing one or more transactivator-responsive promoter elements within a predetermined gene of interest in a second target DNA molecule. Alternatively, control of gene expression by transactivation can be achieved by coexpression of a suppressor tRNA gene and target gene containing a premature stop codon in a plant cell. Furthermore, the invention relates to transgenic plants carrying a DNA molecule coding the transactivator protein or a DNA molecule comprising the gene of interest combined with Lac repressor-responsive elements, crossing of a transgenic plant carrying a gene of interest under control of a Lac repressor/transactivator-sensitive promoter element with a transgenic plant coding for a Lac repressor/transactivator protein and transactivation of expression of a gene of interest. Analogously, the invention relates to transgenic plants carrying a DNA molecule coding a suppressor tRNA or a DNA molecule comprising a target gene which contains a premature stop codon, preferably an amber stop codon, crossing of a transgenic plant carrying a target gene containing a premature stop codon with a transgenic plant coding for the corresponding suppressor tRNA and transactivation of a target gene.