5' PROXIMAL REGIONS OF ARABIDOPSIS NITRATE REDUCTASE GENES DIRECT NITRATE-INDUCED TRANSCRIPTION IN TRANSGENIC TOBACCO

Nitrate reductase (NR) is the first enzyme in nitrate assimilation, a critical process for plant survival. The regulation of NR gene expression is complex, involving both internal and external factors. Of these, nitrate induction of NR gene expression has been studied most extensively and is well conserved among bacteria, fungi, and higher plants. We are interested in understanding the mechanism of nitrate induction of higher plant NR genes. Here we describe promoter analyses of the 5' flanking regions of the Arabidopsis NR genes, NR1 and NR2, with respect to nitrate induction of gene expression. To facilitate these analyses, a nitrate induction procedure using Tt transgenic tobacco plants was established. Approximately 1.5-kb 5' flanking regions of the two Arabidopsis NR genes (NR1 and NR2) were fused to a reporter gene and its expression in transgenic plants was analyzed. Deletion analyses of these regions show that 238- and 188-bp 5' flanking regions of the NR1 and NR2, respectively, contain sequences responsive to nitrate induction.