THE PROMOTER OF THE GENE FOR PLASTIDIC GLUTAMINE-SYNTHETASE (GS2) FROM RICE IS DEVELOPMENTALLY REGULATED AND EXHIBITS SUBSTRATE-INDUCED EXPRESSION IN TRANSGENIC TOBACCO PLANTS

A 1.3-kb fragment from the 5'-flanking region of the RGS-38 gene, which encodes the plastidic glutamine synthetase in Oryza sativa L., was fused to a beta-glucuronidase (GUS) reporter gene and introduced into Nicotiana tabacum by Agrobacterium-mediated transformation. The promoter directed GUS expression, both in leaves and in roots, and the expression of GUS was regulated by light. The GUS activity was high in the mature leaves of the transgenic tobacco plants, in marked contrast to the activity of the GS1 promoter. The GS2 promoter also responded to externally applied ammonia, as is the case for the GS1 promoter. These results suggest that the cis-acting regulatory elements that control the response to ammonia, a substrate for glutamine synthetase, are located within a 1.3-kb region of the promoter.