No abstract

: Sesquiterpenes are found naturally in plants and insects as defensive agents or pheromones. They are produced in the cytosolic acetate/mevalonate pathway for isoprenoid biosynthesis. The inducible sesquiterpene synthases (STS), which are responsible for the transformation of the precursor farnesyl diphosphate, appear to generate very few olefinic products that are converted to biologically active metabolites. In this study, we isolated the STS gene from Panax ginseng C.A. Meyer, designated PgSTS, and investigated the correlation between its expression and various abiotic stresses using real-time PCR. PgSTS cDNA was observed to be 1,883 nucleotides long with an open reading frame of 1,707 bp, encoding a protein of 568 amino acids. The molecular mass of the mature protein was determined to be 65.5 kDa, with a predicted isoelectric point of 5.98. A GenBank BlastX search revealed the deduced amino acid sequence of PgSTS to be homologous to STS from other plants, with the highest similarity to an STS from Lycopersicon hirsutum (55% identity, 51% similarity). Real-time PCR analysis showed that different abiotic stresses triggered significant induction of PgSTS expression at different time points.

Phytocystatins are plant-derived cysteine proteinase inhibitors implicated in the endogenous regulation of protein turnover and defense mechanisms against insects and pathogens. A cysteine proteinase inhibitor, PgCPI, was isolated and characterized from Panax ginseng. Sequence analysis revealed that the coding cDNA sequence of PgCPI is 609 base pairs in length with a predicted molecular mass of 22.5 kDa. A GenBank BlastX search revealed that the deduced amino acid sequence of PgCPI shares a highdegree homology with cysteine proteinase inhibitors from other plants. In this present study, we analyzed the expression patterns of PgCPI against various abiotic and biotic stresses at different time points using quantitative real time-PCR. Enzymatic activity of PgCPI was also determined against cysteine proteinase. Our results reveal that PgCPI is moderately induced by NaCl, chilling, CuSO 4 , ABA, and jasmonic acid. However, high light, UV, MeJA, and wounding triggered a significant induction (more than fourfold) of PgCPI within 12-h post-treatment, especially PgCPI prominently accumulated by wounding (24-fold). In addition, increased transcripts of PgCPI were investigated in fungal-and nematode-infected roots. These results suggest that PgCPI is involved in defense responses to biotic and abiotic stresses.