Abstract: To explore the mode of the spatio-temporal expression of six newly discovered ginsenoside biosynthesis candidate gene transcripts, both Northern blotting and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) were used to elucidate the mRNA expression levels of the transcripts in various tissues and organs of Panax ginseng C. A. Meyer during different growth development stages. The six gene transcripts were all differentially expressed in cultured callus, root, stem, leaf, and seed. The mRNA expression levels were significantly higher in four-year-old roots than in one-year-old roots, and results of semi-quantitative RT-PCR assays were in accordance with those of Northern blotting analyses. The results strongly suggest that all six genes were differentially expressed at root-specific developmental stages. In particular, when a quiescent early stage culture suspension of P. ginseng cells was exposed to the ginsenoside biosynthesis-promoting elicitor Aspergillus niger polysaccharide, the GBR6 gene transcript response showed time-dependent increments and was parallel with ginsenoside productivity (P < 0.01). Overexpression of the GBR6 gene is likely to play a critically important role in the biosynthesis of ginsenosides. The results of the present study provided a background for the further elucidation of the structure and physiological function of these six candidate genes.

Key words: Aspergillus niger polysaccharide, elicitor, GBR6 mRNA expression, ginsenoside　biosynthesis, ginsenoside biosynthesis candidate genes, mRNA differential expression, Panax ginseng C. A. Meyer.