Enhancement of quality of Glycyrrhiza uralensis Fisch. through chitosan induction for use as medicine and food: Insights from metabolomics and proteomics

To explore the impact of exogenous chitosan on the growth and metabolism of Glycyrrhiza uralensis Fisch. ( G . uralensis ) and to improve the quality of cultivated G . uralensis for both medicine and food and aid in the increase in the content of effective components in G . uralensis . In this study, whole G . uralensis plants were treated with exogenous chitosan, and comprehensive analyses of secondary metabolites and proteins were conducted using liquid chromatography with tandem mass spectrometry and isobaric tag for relative and absolute quantitation, respectively. Effects of chitosan induction on endogenous hormones of G . uralensis were analyzed using an enzyme-linked immunosorbent assay. Gene ontology function annotation and Kyoto Encyclopedia of Genes and Genomes pathway annotation were conducted to study the effect of chitosan induction on the proteome. Chitosan induction significantly increased the levels of flavonoids in G . uralensis ; however, the variation in triterpenoids was not substantial. Biological processes, including photosynthesis, secondary metabolism, and abiotic stress responses, were significantly enriched. Additionally, the photosynthetic pathway, photosynthesis-antenna protein pathway, and plant hormone signal transduction pathway were significantly enriched. In the flavonoid biosynthesis pathway, the upstream-related enzyme phenylalanine ammonia-lyase (PAL) and the downstream-related enzymes chalcone synthase (CHS), polyketide reductase (PKR), chalcone isomerase (CHI), and vestitone reductase (VR) were significantly upregulated. Our findings suggest that chitosan induction may promote the tricarboxylic acid (TCA) cycle, and the TCA cycle enhancement significantly upregulated PAL, CHS, PKR, CHI, and VR, the five key enzymes involved in flavonoid synthesis of G . uralensis , indicating that chitosan induction activated the entire metabolic pathway associated with flavonoids in G . uralensis . Our findings provide a reference for improving the quality of cultivated G . uralensis from the perspective of pharmacodynamic components.