Identification and characterization of spermidine synthase gene from Panax ginseng

A full length spermidine synthase (PgSPD) cDNA was isolated and characterized from the root of Panax ginseng C. A. Meyer. The cDNA was 1,188 nucleotides long and had an open reading frame of 1,002 bp with a deduced amino acid sequence of 333 residues. The calculated molecular mass of the matured protein is approximately 36.38 kDa with a predicated isoelectric point of 5.02. A GenBank BlastX search revealed that the deduced amino acid of PgSPD shares a high degree homology with the Lotus japonicas (78.5% identity, 84% similarity). In the present study we analyzed the expression of PgSPD under various environmental stresses at different time points using real time-PCR. We also determined polyamine content in adventitious roots under salt and chilling stress using HPLC. Our results reveal that PgSPD is slightly induced by mannitol and CuSO4. Otherwise, salt, chilling, abscisic acid and jasmonic acid triggered a significant induction (more than tenfold) of PgSPD within 12-24 h post-treatment, especially; PgSPD was prominently induced by salt (41.5-fold). These results suggest that the transcript of Spd gene involved in PA biosynthesis shows different profiles of expression in response to environmental stress.