A COMPARISON OF THE ACTIVITY OF 3 CAULIFLOWER MOSAIC-VIRUS 35S PROMOTERS IN RICE SEEDLINGS AND TOBACCO (BY-2) PROTOPLASTS BY ANALYSIS OF GUS REPORTER GENE TRANSIENT EXPRESSION

The cauliflower mosaic virus (CaMV) 35S promoter is active in most pla nt species and has been used for genetic engineering to obtain strong, constitutive expression of numerous, unrelated genes. We examined the transient expression of constructs in which the uidA (GUS) reporter g ene was driven by three somewhat different, independently isolated CaM V 35S promoters. These CaMV 35S promoters differed principally in 5-6 bases outside the region containing cis-acting regulatory elements, bu t they were identical in sequences within known regulatory elements. P lasmid DNA containing the chimeric constructs was delivered to protopl asts derived from cultured BY-2 tobacco cells by electroporation and t o rice embryos by DNA uptake during imbibition. GUS enzyme activity wa s determined by a fluorometric method 72 h after protoplast electropor ation. The rice embryos were germinated after DNA uptake during imbibi tion and GUS activity was determined histochemically and fluorometrica lly in 7-day-old seedlings. All three CaMV 35S promoters gave similar levels of GUS expression in rice seedlings, both in terms of the patte rn of expression in the various seedling tissues and in terms of the t otal level of GUS activity per seedling. In contrast, there was nearly a 14-fold difference in the activity of the promoters in the tobacco protoplasts. Promoter activity in tobacco appeared to be strongly affe cted by the sequence near the transcriptional start site where the pro moters differed. These results suggest that monocots and dicots may ut ilize somewhat different signals for transcription initiation.