COPPER-CONTROLLABLE GENE-EXPRESSION SYSTEM FOR WHOLE PLANTS

We describe a system for gene expression in plants based on the regula tion mechanism of the yeast metallothionein (MT) gene. The system cons ists of two elements: (i) the yeast ace1 (activating copper-MT express ion) gene encoding a transcription factor under control of the caulifl ower mosaic virus (CaMV) 35S RNA promoter, and (ii) a gene of interest under control of a chimeric promoter consisting of the 90-base-pair d omain A of the CaMV 35S RNA promoter linked to the ACE1 transcription factor-binding site. At elevated copper ion concentrations, the ACE1 p rotein changes conformation, binds to, and activates transcription fro m the chimeric promoter. To test the functioning of the system in plan ts, a construct containing the beta-glucuronidase (GUS) reporter gene under control of the chimeric promoter was prepared, and transgenic to bacco plants were produced. It was shown that GUS activity in the leav es of transgenic plants increased up to 50-fold, either after addition of 50 muM CuSO4 to the nutrient solution or after application of 0.5 muM CuSO4 to the plants in a foliar spray. This GUS expression was rep ressed after the removal of copper ions. The results show that the act ivity of the described chimeric promoter directly depends on copper io n concentration and that this system can be used in experiments that d emand precise timing of expression.