REGULATION OF CONSTITUTIVE GENE EXPRESSION IN PLANTS: GENETIC ANALYSIS OF THE NOPALINE SYNTHASE PROMOTER

n Agrobacterium Ti plasmid vector was used for the analysis of the in vitro mutagenized nopaline synthase (nos) promoter. This promoter is constitutively active in a wide range of plants and tissues. The chloramphenicol acetyltransferase (CAT) reporter gene was used to indirectly determine transcriptional activity of the promoter in stably and transiently transformed tobacco tissues. Stable transformation assays revealed the presence of at least three promoter elements: a TATA box, a CCAAT box region, and an upstream essential element. Deletion of these elements results in 10-15%, 5% and 0% of wild type levels of CAT activity.;Electroporation mediated transient analysis of the CCAAT and TATA box deletion mutants gave values which were three or fourfold higher than those obtained for the stably transformed mutants. The essential element responded similarly in both assay systems: duplication of the entire essential element tripled CAT activity, while deletion of the entire element eliminated CAT activity. However, deletion of the repeat domain of the essential element gave 45% vs. 3% of wild type activity under transient vs. stable assay classes conditions. The different responses of the two classes of essential element mutation (repeat vs. total deletion) support the existence for two domains within the element.;The element was only 1.3 to 3.8% as active in the reverse vs. the wild type orientation when linked to the nonfunctional 5;The nos gene is also transcribed and translated in Agrobacterium. Since only the TATA box is shared between the prokaryotic and eukaryotic promoters, it serves as a useful model plant promoter.;A 19 bp deletion,...