Identification and characterization of differentially expressed genes involved in pharmacological activities of roots of Panax notoginseng during plant growth

Panax notoginseng is a highly valued Chinese medicinal herb. To understand the molecular mechanism of the much higher pharmacological activities of roots of 3-year-old plants over 1-year-old ones,two cDNA libraries were constructed using the suppression subtractive hybridization (SSH) method. Positive cDNA clones from each of the two libraries were randomly selected for dot-blotting analysis. A total of 110 genes were highly expressed in 3-year-old roots and 80 genes in 1-year-old roots. Of these, 87 cDNA fragments were sequenced, assembled, and compared with sequences in GenBank, and 81 individual cDNAs were identified. These cDNAs were the first expressed sequence tags of P. notoginseng in GenBank. The result of reverse transcription PCR analysis of six genes was consistent with that of the dot-blot analysis. The global gene expression profile showed that there were significant differences between 1- and 3-year-old roots of P. notoginseng plants. Some important structural and regulatory genes which may be involved in isoprenoid biosynthesis were found to be over-expressed in 3-year-old roots, such as genes encoding 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphat-synthase (IspG-protein), multi-copper oxidase type I family protein, NADH flavin oxidoreductase, lipase and aconitase.