Integrative analysis of the pharmaceutical active ingredient and transcriptome of the aerial parts of Glycyrrhiza uralensis under salt stress reveals liquiritin accumulation via ABA-mediated signaling

The aerial parts of Glycyrrhiza uralensis supply substantial raw material for the extraction of active pharmaceutical ingredients comprehensively utilized in many industries. Liquiritin is the unique and most abundant flavonoid active component in G. uralensis. It has a wide range of pharmacological activities and high economic value. Our previous study indicated that moderate salt stress increased the content of active ingredients. However, the regulatory mechanism remains unclear. In this study, RNA-sequencing (RNA-seq) of the aerial parts of G. uralensis treated with 150 mM NaCl for 0, 2, 6, and 12 h was performed to identify the key genes and metabolic pathways regulating pharmacological active component accumulation. The main active component detection showed that liquiritin was the major ingredient and exhibited more than a 10-fold significant increase in the 6-h NaCl treatment. Temporal expression analysis of the obtained 4245 differentially expressed genes (DEGs) obtained by RNA-seq revealed two screened profiles that included the significant up-regulated DEGs (UDEGs) at different treatment points. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of these UDEGs identified phenylpropanoid metabolism and flavonoid biosynthesis as the most significantly enriched pathways in 2-h treated materials. Interestingly, the carotenoid biosynthesis pathway that is related to ABA synthesis was also discovered, and the ABA content was significantly promoted after 6-h NaCl treatment. Following ABA stimulation, the content of liquiritin demonstrated a significant and immediate increase after 2-h treatment, with the corresponding consistent expression of genes involved in the pathways of ABA signal transduction and flavonoid biosynthesis, but not in the pathway of glycyrrhizic acid biosynthesis. Therefore, salt stress might promote liquiritin accumulation through the ABA-mediated signaling pathway in G. uralensis. Our study provides candidate genes and pathways controlling liquiritin synthesis, and would drive progress in genetic improvement and promote the comprehensive utilization of the aerial part of G. uralensis. Overall design: RNA-sequencing (RNA-seq) of the aerial parts of G. uralensis treated with 150 mM NaCl for 0, 2, 6, and 12 h was performed to identify the key genes and metabolic pathways regulating pharmacological active component accumulation.