Abstract
Long-term cultivation of Panax ginseng cell lines leads to a decreasing synthesis of the biologically active substances used in traditional medicine. To gain insight into the cellular mechanisms which may influence this process, we analyzed variations within the rDNA cluster of the Oriental ginseng cell lines. The cell lines were cultivated for 6 and 24 years; the number of nucleoli and chromosomes was analyzed. The complete 18S rDNA sequences were cloned and sequenced. The nucleotide polymorphism and phylogenetic relations of the sequences were analyzed, and the secondary structures for separate 18S rRNA regions were modeled. The 18S rDNA accumulated mutations during cell cultivation that correlate well with an increase in the number of chromosomes and nucleoli. The patterns of nucleotide diversity are culture-specific and the increasing polymorphism associates with cytosine methylation sites. The secondary structures of some 18S rRNA regions and their interaction can alter during cultivation. The phylogenetic tree topologies are particular for each cell line.The observed alterations in rDNA clusters are associated with a somaclonal variation, leading to changes in the pattern of intracellular synthesis during cell cultivation. The identified divergent rRNAs could provide additional gene expression regulation in P. ginseng cells by forming heterogeneous ribosomes.
Highlights
Panax ginseng Meyer is one of the most valuable herbs used in Chinese traditional medicine
The purpose of this study was to determine the patterns of intragenomic nucleotide polymorphism in the complete 18S rDNA sequences of Panax ginseng cell lines, which are different at the time of cultivation and in the tissue source
We focused our attention on the nucleotide polymorphism of the cell cultures in order to determine whether the existence of differences among 18S rDNA sequences could decrease the ginsenoside biosynthesis
Summary
Panax ginseng Meyer is one of the most valuable herbs used in Chinese traditional medicine. Plant cell cultures are a promising source for the large-scale and cost-effective production of high-purity valuable secondary metabolites. Plant cell lines have attracted scientists’ attention due to their ability to produce biologically active substances with strong therapeutic effects against various diseases and aging [1,2,3,4,5], and ginseng cell lines are proposed to be a valuable source of the unique biologically active saponins called ginsenosides. Cell lines often lose their ability to produce biologically active substances during long-term cultivation, and there are very few successful examples of their utilization for the commercial production of secondary metabolites (e.g., shikonin and paclitaxel) [1,2,3,4]. The true reasons for this instability are still unknown, and should be clarified for the successful exploitation of plant cell lines for the purposes requiring long-term cultivation
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