Comparative Transcriptomic Analysis on White and Blue Flowers of Platycodon grandiflorus to Elucidate Genes Involved in the Biosynthesis of Anthocyanins

Background: Platycodon grandiflorus has long been used in Northeast Asia as a food and folk medicine to treat various diseases. The intense blue color of P. grandiflorus corolla is its characteristic feature. Objectives: By comparing deep transcriptomic data of P. grandiflorus and its white cultivar, we intended to elucidate the molecular mechanisms concerning the biosynthesis of anthocyanins in this plant. Material and Methods: We sampled blue mature flowers (PgB) and yellow young buds (PgY) of P. grandiflorus. Meanwhile, mature flowers (PgW) of P. grandiflorus white cultivar were also collected for RNA extraction and nextgeneration sequencing. After high-throughput sequencing, Trinity software was applied for de novo assembly and the resultant 49934 unigenes were subjected for expression analysis and annotation against NR, KEGG, UniProt, and Pfam databases. Results: In all, 32.77 Gb raw data were generated and the gene expression profile for the flowers of P. grandiflorus was constructed. Pathway enrichment analysis demonstrated that genes involved in flavone and flavonol biosynthesis were differently expressed. Conclusions: The extremely low expression of flavonoid-3',5'-hydroxylase in PgY and PgW was regarded as the reason for the formation of its white cultivar. Our findings provided useful information for further studies into the biosynthetic mechanism of anthocyanins.