Differential expression of two members of the nuclear gene family encoding arginine decarboxylase in tobacco (Nicotiana tabacum L)

Two nuclear genes (NtADC-1 and Nt ADC-2) encoding arginine decarboxylase (ADC, EC 4.1.1.19) have been characterized from Nicotiana tabacum cv Xanthi and their differential expression during development analyzed. The two nuclear genes are 95% identical in nucleotide sequence within their coding and 5'-and 3' noncoding regions. Both genes contain a single open reading frame, uninterrupted by introns, encoding proteins of 720 (ADC1) and 721 (ADC2) amino acids. The predicted amino acid sequence of ADC1 is identical to that encoded by the cDNA PR24 previously isolated from N. tabacum cv Burley 21, and differs at 22 amino acids residues from ADC2 (96.4% identical). Transcripts encoding ADC1 and ADC2 are expressed predominantly in the root and floral tissues of wild-type tobacco plants. A small, transient increase in ADC transcript abundance is observed in the roots of wild type Burley 21 tobacco within 24 h after topping (i.e., removal of the floral meristem and upper leaves and stem). Low alkaloid (nic1 nic2) mutants subjected to the same treatment showed no induction in ADC expression. Using semi-quantitative RT-PCR analysis and synthetic oligonucleotide primers capable of distinguishing between the two different ADC transcripts, it has been shown that NtADC2 is preferentially expressed in roots and accounts for the major portion of ADC transcripts present.