Expression of arginine decarboxylase is induced during early fruit development and in young tissues of Pisum sativum (L.).

A cDNA coding for arginine decarboxylase (ADC, EC 4.1.1.19) has been isolated from a cDNA library of parthenocarpic young fruits of Pisum sativum (L.). The deduced aminoacid sequence is 74%, 46% and 35% identical to ADCs from tomato, oat and Escherichia coli, respectively. When the pea ADC cDNA was put under the control of the galactose inducible yeast promoter CYC1-GAL10 and introduced into Saccharomyces cerevisiae, it conferred galactose-regulated expression of the ADC activity. The ADC activity expressed in S. cerevisiae was inhibited 99% by alpha-DL-difluoromethylarginine (DFMA), a specific inhibitor of ADC activity. No activity was detected in the untransformed S. cerevisiae, nor when it was transformed with an antisense ADC construct. This provides direct evidence that the ADC cDNA from pea encoded a functional, specific ADC activity and that S. cerevisiae is able to process correctly the protein. In the pea plant, gene expression of the ADC is high in young developing tissues like shoot tips, young leaflets and flower buds. Fully expanded leaflets and roots have much lower, but still detectable, levels of the ADC transcript. In the ovary and fruit, they are developmentally regulated, showing high levels of expression during the early stages of fruit growth, which in pea is mainly due to cell expansion. The observed changes in the steady-state levels of ADC mRNA alone, however, cannot account for the differences in ADC activity suggesting that other regulatory mechanisms must be acting.