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Summary To investigate promoter strength and the tissue‐specific patterns of expression, chimeric promoters incorporating subdomains of mannopine synthase ( mas 2′) and octopine synthase ( ocs ) promoter and activator regions were affixed to a β‐glucuronidase reporter gene and the constructions 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 examined. In leaf tissue, this chimeric promoter is approximately 156‐fold 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 types. Addition of the ocs or mas UAS to the mas or ocs promoter/activator regions modulated these expression patterns. The addition of a trimer of the ocs UAS to the mas promoter/activator region resulted in a transcriptional control element that directed GUS expression in most cell types. In addition to the strong expression in transgenic tobacco plants, this novel promoter directed higher levels of GUS expression than did the CaMV 35S promoter in transiently transformed tobacco leaf discs and suspension culture cells, as well as in cassava and cowpea explants. It is proposed that the strong promoter containing a trimer of 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.
Ni et al. (Sat,) studied this question.