A Candidate Gene Identified in Converting Platycoside E to Platycodin D by Correlating Main Metabolites Content with Gene Expression Variation between Callus and Leaf of Platycodon grandiflorus
Platycodon grandiflorus is a perennial traditional Chinese herb, which has more than 100 compounds including triterpenoid saponins, polysaccharides and phenolic acid etc. In this study, a (L9(34)) orthogonal experiment determined the optimal explants is stem with nodes and the optimum full medium is MS + NAA 1.0 mg/L + 6-BA 0.5 mg/L as best protocol for callus induction of P. grandiflorus.The content of platycodin D, platycoside E and total polysaccharides between callus and plant organs is significantly difference, and the distribution of platycodin D, platycoside E and total polysaccharide in whole plant has been clarified. Meanwhile, the content of platycodin D and total polysaccharide were found higher in calli than in leaves or the whole plant. While, the content of platycoside E in calli is very lower than in leaves. In order to screen candidate genes involved in platycoside E and platycodin D conversion, a RNA-Seq analysis between calli and leaves was performed. Correlating the content of platycodin D and platycoside E between calli and leaves with the gene expression level involving in triterpenoid saponin biosynthesis pathway, four cluster genes with high amino acid similarity were screened as the putative sequences of ß-Glucosidase gene for converting platycoside E to platycodin D. It was found that the expression level of genes encoding enzymes involved in saponins and polysaccharides biosynthesis was co-expression with the content of the corresponding metabolite. Besides, some transcription factors predicted to regulate the expression of key enzymes involving in triterpernoid saponins and polysaccharides biosynthesis pathway of P. grandiflorus. Overall design: Try to find ß-glucosidase gene in plants to transform Platycoside E to Platycoside D