DELETION ANALYSIS OF A NITRITE-REDUCTASE PROMOTER FROM SPINACH IN TRANSGENIC TOBACCO

Deletion analysis of the nitrite-reductase (NiR) promoter from spinach (Spinacia oleracea L.) fused to the beta-glucuronidase (GUS) reporter gene and introduced into tobacco (Nicotiana tabacum L., cv. Coker 176) indicates that basic elements required for light- and nitrate-dependent expression of the reporter are located within the promoter sequence -200/+131 relative to the transcription-initiation site. Detailed analysis indicates that positive regulatory elements exist between -200 and -330 as well as between -1450 and -1730, stimulating the level of GUS gene expression under all experimental conditions. Induction/reversion light-pulse experiments show that the promoter sequence -200/+131 suffices for phytochrome-mediated expression of the reporter gene. The observation that the NiR promoter from spinach exhibits full reversibility in transgenic tobacco confirms the previous conclusion that the NiR promoter from spinach fused to a GUS reporter gene and introduced into tobacco responds to nitrate and phytochrome as would be expected for tobacco (host) and not as would be expected for spinach (donor). When the plastids were damaged by photooxidation in the presence of Norflurazon, GUS activity levels were reduced to the same extent for all NiR-promoter/GUS fusions tested, indicating that the promoter region involved in the action of the 'plastidic factor' is between -200 and +131. The GUS gene expression under the control of the CaMV-35S promoter is not affected by light, nitrate or the 'plastidic factor'.