MOLECULAR-CLONING AND FUNCTIONAL IDENTIFICATION OF A PLANT ORNITHINE DECARBOXYLASE CDNA

A cDNA for a plant ornithine decarboxylase (ODC), a key enzyme in putr escine and polyamine biosynthesis, has been isolated from root culture s of the solanaceous plant Datura stramonium. Reverse transcription-PC R employing degenerate oligonucleotide primers representing conserved motifs from other eukaryotic ODCs was used to isolate the cDNA. The lo ngest open reading frame potentially encodes a peptide of 431 amino ac ids and exhibits similarity to other eukaryotic ODCs, prokaryotic and eukaryotic arginine decarboxylases (ADCs), prokaryotic meso-diaminopim elate decarboxylases and the product of the tabA gene of Pseudomonas s yringae cv. tabaci. Residues involved at the active site of the mouse ODC are conserved in the plant enzyme. The plant ODC does not possess the C-terminal extension found in the mammalian enzyme, implicated in rapid turnover of the protein, suggesting that the plant ODC may have a longer half-life, Expression of the plant ODC in Escherichia coli an d demonstration of ODC activity confirmed that the cDNA encodes an act ive ODC enzyme. This is the first description of the primary structure of a eukaryotic ODC isolated from an organism where the alternative A DC route to putrescine is present.