Integrated Metabolomics and Transcriptomics Analyses Highlight the Flavonoid Compounds Response to Alkaline Salt Stress in Glycyrrhiza uralensis Leaves

Glycyrrhiza uralensis is a saline-alkali-tolerant plant whose aerial parts are rich in flavonoids; however, the role of these flavonoids in saline-alkali tolerance remains unclear. Herein, we performed physiological, metabolomics, and transcriptomics analyses in G. uralensis leaves under alkaline salt stress for different durations. Alkaline salt stress stimulated excessive accumulation of reactive oxygen species and consequently destroyed the cell membrane, causing cell death, and G. uralensis initiated osmotic regulation and the antioxidant system to respond to stress. In total, 803 metabolites, including 244 flavonoids, were detected via metabolomics analysis. Differentially altered metabolites and differentially expressed genes were coenriched in flavonoid-related pathways. Genes such as novel.4890, Glyur001511s00039602, and Glyur000775s00025737 were highly expressed, and flavonoid metabolites such as 2'-hydroxygenistein, apigenin, and 3-O-methylquercetin were upregulated. Thus, flavonoids as nonenzymatic antioxidants play an important role in stress tolerance. These findings provide novel insights into the response of G. uralensis to alkaline salt stress.