Multi-Omics Elucidates Difference in Accumulation of Bioactive Constituents in Licorice (Glycyrrhiza uralensis) under Drought Stress

Licorice is a frequently applied herb with potential edible and medicinal value based on various flavonoids and triterpenes. However, studies on detailed flavonoid and triterpene metabolism and the molecular basis of their biosynthesis in licorice are very limited, especially under drought conditions. In the present study, we carried out transcriptome, proteome, and metabolome experiments. To ultimately combine three omics for analysis, we performed a bioinformatics comparison, integrating transcriptome data and proteome data through a Cloud platform, along with a simplified biosynthesis of primary flavonoids and triterpenoids in the KEGG pathway based on metabolomic results. The biosynthesis pathways of triterpenes and flavonoids are enriched at both gene and protein levels. Key flavonoid-related genes (PAL, 4CL, CHS, CHI, CYP93C, HIDH, HI4OMT, and CYP81E1_7) and representative proteins (HIDH, CYP81E1_7, CYP93C, and VR) were obtained, which all showed high levels after drought treatment. Notably, one R2R3-MYB transcription factor (Glyur000237s00014382.1), a critical regulator of flavonoid biosynthesis, achieved a significant upregulated expression as well. In the biosynthesis of glycyrrhizin, both gene and protein levels of bAS and CYP88D6 have been found with upregulated expression under drought conditions. Most of the differentially expressed genes (DEGs) and proteins (DEPs) showed similar expression patterns and positively related to metabolic profiles of flavonoid and saponin. We believe that suitable drought stress may contribute to the accumulation of bioactive constituents in licorice, and our research provides an insight into the genetic study and quality breeding in this plant.