THE REGULATORY REGIONS OF THE RICE TUNGRO BACILLIFORM VIRUS PROMOTER AND INTERACTING NUCLEAR FACTORS IN RICE (ORYZA-SATIVA L)

Rice Tungro Bacilliform Virus (RTBV) promoter confers phloem-specific gene expression in transgenic rice plants. A series of promoter deleti on mutants were fused with the Escherichia coli beta-glucuronidase A ( uidA) reporter gene and introduced into transgenic rice plants. The RT BV promoter confers substantially stronger expression in shoots than i n roots. A fragment of the promoter comprising nucleotides -164 to +45 relative to the transcriptional start site contains sufficient inform ation for phloem-specific gene expression. Within this region, nucleot ides -164 to -43 were essential for promoter function since deletion o f this fragment dramatically reduced promoter activity. Gel-retardatio n assays identified two groups of rice nuclear factors (RNFG1 and RNFG 2) that bind to the -164 to +45 promoter fragment. Competition and DNa sel footprinting experiments indicated that RNFG1 bound to nucleotides -3 to +8 (Box I) while RNFG2 bound to nucleotides -53 to -39 (Box II) . Interactions between the two groups of factors were observed. In add ition, we found differences in the binding of nuclear factors from sho ots versus from roots, in agreement with the different activities of t he promoter in these two organs. It is proposed that binding of RNFG1 and RNFG2 between nucleotides -164 to +45 is essential for the tissue- specific expression of this promoter.