STRENGTH AND TISSUE-SPECIFICITY OF CHIMERIC PROMOTERS DERIVED FROM THE OCTOPINE AND MANNOPINE SYNTHASE GENES

To investigate promoter strength and the tissue-specific patterns of e xpression, chimeric promoters incorporating subdomains of mannopine sy nthase (mas2') and octopine synthase (ocs) promoter and activator regi ons were affixed to a beta-glucuronidase reporter gene and the constru ctions introduced into tobacco plants. Addition of a trimer of the ocs upstream activating sequence (UAS) to a mas promoter/activator region resulted in highly elevated levels of GUS activity in all tissues exa mined. In leaf tissue, this chimeric promoter is approximately 156-fol d and 26-fold stronger than are the CaMV 35S and the 'enhanced' double CaMV 35S promoters, respectively. Expression of GUS activity directed by the mas and ocs promoters/activators is limited to specific cell t ypes. Addition of the ocs or mas UAS to the mas or ocs promoter/activa tor regions modulated these expression patterns. The addition of a tri mer of the ocs UAS to the mas promoter/activator region resulted in a transcriptional control element that directed GUS expression in most c ell types. In addition to the strong expression in transgenic tobacco plants, this novel promoter directed higher levels of GUS expression t han did the CaMV 35S promoter in transiently transformed tobacco leaf discs and suspension culture cells, as well as in cassava and cowpea e xplants. It is proposed that the strong promoter containing a trimer o f the ocs UAS affixed to the mas promoter/activator will be useful for the very high level constitutive expression of linked genes in a wide variety of plant species.