Exploring the genes involved in biosynthesis of dihydroquercetin and dihydromyricetin in Ampelopsis grossedentata

Dihydroquercetin (DHQ), an extremely low content compound (less than 3%) in plants, is an important component of dietary supplements and used as functional food for its antioxidant activity. Moreover, as downstream metabolites of DHQ, an extremely high content of dihydromyricetin (DHM) is up to 38.5% in Ampelopsis grossedentata. However, the mechanisms involved in the biosynthesis and regulation from DHQ to DHM in A. grossedentata remain unclear. In this study, a comparative transcriptome analysis of A. grossedentata containing extreme amounts of DHM was performed on the Illumina HiSeq 2000 sequencing platform. A total of 167,415,597 high-quality clean reads were obtained and assembled into 100,584 unigenes having an N50 value of 1489. Among these contigs, 57,016 (56.68%) were successfully annotated in seven public protein databases. From the differentially expressed gene (DEG) analysis, 926 DEGs were identified between the B group (low DHM: 210.31 mg/g) and D group (high DHM: 359.12 mg/g) libraries, including 446 up-regulated genes and 480 down-regulated genes (B vs. D). Flavonoids (DHQ, DHM)-related DEGs of ten structural enzyme genes, three myeloblastosis transcription factors (MYB TFs), one basic helix-loop-helix (bHLH) TF, and one WD40 domain-containing protein were obtained. The enzyme genes comprised three PALs, two CLs, two CHSs, one F3'H, one F3'5'H (directly converts DHQ to DHM), and one ANS. The expression profiles of randomly selected genes were consistent with the RNA-seq results. Our findings thus provide comprehensive gene expression resources for revealing the molecular mechanism from DHQ to DHM in A. grossedentata. Importantly, this work will spur further genetic studies about A. grossedentata and may eventually lead to genetic improvements of the DHQ content in this plant.