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The expressed sequence tags (ESTs) referenced in this report are the first transcriptomes in a leaf from a half-shade ginseng plant. A cDNA library was constructed from samples of the leaves of 4-year-old Panax ginseng plants, which were cultured in a field. The 2,896 P. ginseng cDNA clones represent 1,576 unique sequences, consisting of 1,167 singletons and 409 contig sequences. BLAST comparisons of the cDNAs in GenBank's non-redundant databases revealed that 2,579 of the 2,896 cDNAs (89.1%) exhibited a high degree of sequence homology to genes from other organisms. The majority of the identified transcripts were found to be genes related with energy, metabolism, subcellular localization, and protein synthesis and transport. The chlorophyll a/b-binding protein ESTs in the ginseng leaf samples manifested a substantially higher level of expression than was observed in other plant leaves. The ESTs involved in ginsenoside biosynthesis were also identified and discussed.

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Glutamate decarboxylase (GAD) catalyzes the conversion of L-glutamate to γ-aminobutyric acid (GABA). A full-length cDNA encoding GAD (designated as PgGAD) was isolated and characterized from the root of Panax ginseng C. A. Meyer. The length cDNA of PgGAD was 1881 bp and contained a 1491 bp open reading frame (ORF) encoding a glutamate decarboxylase protein of 496 amino acids, possessing a Ser-X-X-Lys active site, which belongs to the GAD group. The deduced amino acid sequence of the PgGAD was classified in the plant GAD family and has 76-85% high similarity with other plants as like petunia, Arabidopsis, tomato. Secondary structure of PgGAD was predicted by using SOPMA software program. Southern blot analysis of genomic DNA suggests that, there is more than one copy of the PgGAD gene. The organ specific gene expression pattern also studied in P. ginseng seedlings, in which the stem showed elevated expression than root, leaf, bud and rhizomes. Along with this, we also confirmed the gene expression of PgGAD under various abiotic stresses like temperature stress, osmotic stress, anoxia, oxidative stress, and mechanical damage. Temporal analysis of gene expression except exposure of oxidative stress revealed an enhanced expression after each stresses. The enzyme activity of PgGAD was stimulated to 2-fold under cold stress.

The role of plant chitinases in protecting plants against a variety of fungal pathogens is well established. In the present study, a cDNA clone containing a class I chitinase (Chi-1) gene, designated as PgChi-1, has been isolated from the oriental medicinal plant Panax ginseng. PgChi-1 is predicted to encode a protein of 34.9 kDa consisting of 323 amino acid residues. PgChi-1 was found to be expressed constitutively in all of the studied organs of ginseng plant. Under various abiotic stress treatments including Cu, H2O2, mannitol, SA, JA, and NaCl, the expression of PgChi-1 in plantlets and hairy roots increased significantly compared to the control. When different parts of root were analyzed, maximum level was observed in taproot. In addition, levels of PgChi-1 expression were compared between healthy root and fungal, bacterial, and nematode infected root. Significant increase of PgChi-1 was noticed in pathogen infected roots than healthy roots. This study revealed that PgChi-1 may protect the P. ginseng under both biotic and abiotic stress conditions.