Combined transcriptomic and metabolomic analyses reveal the pharmacognostic mechanism of the metabolism of flavonoids in different parts of Polygonum capitatum.

The plant Polygonum capitatum (P. capitatum) contains a variety of flavonoids that are distributed differently among different parts. Nevertheless, differentially expressed genes (DEGs) associated with this heterogeneous distribution have not been identified. In this study, combined with transcriptomic and metabonomic analysis, we identified significant DEGs related to variations in flavonoid composition among different parts of P. capitatum. Subsequently, transcriptomic and nontargeted metabolomic analyses revealed that flavonoids and phenolic acids in different parts of P. capitatum were significantly enriched in the phenylpropanoid biosynthesis, shikimic acid biosynthesis, and flavonoid biosynthesis pathways. The expression levels of genes encoding enzymes, including shikimate O-hydroxycinnamoyltransferase (HCT), chalcone synthase (CHS), flavonoid 3',5'-hydroxylase (CYP75A), flavones 3-hydroxylase (F3H), flavonol synthase (FLS), leucoanthocyanidin reductase (LAR), trans-cinnamate 4-monooxygenase (CYP73A), and shikimate kinase (SK), were found to be the lowest in the leaves of P. capitatum via quantitative PCR. Interestingly, these genes are involved in the biosynthesis of quality markers such as gallic acid, quercetin, and quercitrin in P. capitatum. Finally, the targeted metabolomic results reconfirmed that the gallic acid, quercetin, and quercitrin contents were the highest in the leaves of P. capitatum. This research provides a theoretical basis for further understanding the differential regulatory mechanism of flavonoid metabolism in different parts of P. capitatum, providing novel insights into the pharmacognostic basis of P. capitatum.