TISSUE-SPECIFIC EXPRESSION AND TEMPORAL REGULATION OF THE RICE GLUTELIN GT3 GENE ARE CONFERRED BY AT LEAST 2 SPATIALLY SEPARATED CIS-REGULATORY ELEMENTS

The rice glutelin Gt3 promoter was fused to a beta-glucuronidase (GUS) reporter gene and its expression evaluated in transgenic tobacco plan ts. Histochemical analysis revealed that the expression of the introdu ced Gt3 promoter/GUS (beta-glucuronidase) chimeric gene was confined t o endosperm tissue of developing seeds. 5'-promoter deletion analysis revealed that two domains of the Gt3 promoter, -346 to -263 bp (domain I) and -945 to -726 bp (domain II) from the transcriptional start sit e, were essential for optimum expression of the GUS reporter gene. Rem oval of 5' sequences upstream of -726 resulted in a reduction in overa ll promoter activity and a shift in temporal expression from a maximum of 16-20 days after flowering to 24 days. Removal of DNA sequences fr om the 5' end to -346 yielded a promoter fragment that was still able to confer endosperm-specific expression, although a further deletion t o -263 abolished promoter activity. These data suggest that at least t wo cis-regulatory elements are required for endosperm specificity and temporal regulation of glutelin Gt3 gene expression.