ACTIVITY OF A MAIZE UBIQUITIN PROMOTER IN TRANSGENIC RICE

We have used the maize ubiquitin 1 promoter, first exon and first intr on (UBI) for rice (Oryza sativa L. cv. Taipei 309) transformation expe riments and studied its expression in transgenic calli and plants. UBI directed significantly higher levels of transient gene expression tha n other promoter/intron combinations used for rice transformation. We exploited these high levels of expression to identify stable transform ants obtained from callus-derived protoplasts co-transfected with two chimeric genes. The genes consisted of UBI fused to the coding regions of the uidA and bar marker genes (UBI:GUS and UBI:BAR). UBI:GUS expre ssion increased in response to thermal stress in both transfected prot oplasts and transgenic rice calli. Histochemical localization of GUS a ctivity revealed that UBI was most active in rapidly dividing cells. T his promoter is expressed in many, but not all, rice tissues and under goes important changes in activity during the development of transgeni c rice plants.