Cloning and abiotic stress responsive expression analysis of Arginine decarboxylase genes in contrasting rice genotypes

Arginine decarboxylase (ADC) is the first enzyme of polyamine biosynthesis in plants, an important mediator of abiotic stress tolerance. Two genes OsADC1 and OsADC2 were found to be differentially expressed under various abiotic stresses namely salinity, drought, low temperature and high temperature. Significant differences in gene expression were found among contrasting rice genotypes Nerica-L-44 (NL44; tolerant) and Pusa Sugandh 2 (PS2; sensitive). Among the homologs, OsADC2 was induced frequently in abiotic stresses with a higher transcript level than OsADC1. When the stress dependent gene expression was estimated relative to control conditions, PS2 showed a significant and higher level of induction. The estimation of relative gene expression between genotypes for each stress in all shoot tissues showed significantly higher level of expression in NL44 than PS2. In roots, the stress induced expression was higher in the sensitive genotype PS2. Construction of phylogenetic tree provided an insight on the evolution of OsADC gene from lower to higher organisms. The OsADC2 gene was found to be highly diverged from OsADC1 as well as from the counterparts of related and distant taxa. The analysis of amino acid sequence identified the conserved substrate binding, cofactor binding and dimerisation domains essential for enzyme activity.