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 express ion is complex, involving both internal and external factors. Of these , nitrate induction of NR gene expression has been studied most extens ively 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 respe ct to nitrate induction of gene expression. To facilitate these analys es, a nitrate induction procedure using Tt transgenic tobacco plants w as established. Approximately 1.5-kb 5' flanking regions of the two Ar abidopsis NR genes (NR1 and NR2) were fused to a reporter gene and its expression in transgenic plants was analyzed. Deletion analyses of th ese regions show that 238- and 188-bp 5' flanking regions of the NR1 a nd NR2, respectively, contain sequences responsive to nitrate inductio n.