Comparative iTRAQ Proteomic Analysis Provides the Molecular Basis of the Metabolites in Cultivated Glycyrrhiza uralensis and its Wild-Type

Background: Licorice is an herbal medicine applied extensively worldwide, and most of the licorice for clinical consumption is provided by Glycyrrhiza uralensis Fisch. Evidence suggests that there is a significant difference in the metabolite composition of licorice from different ecotypes. Objective: To better understand the proteomic changes and molecular mechanisms of metabolite formation in wild and cultivated Glycyrrhiza uralensis Fisch. Methods: Firstly, we established a proteome database by annotating protein sequences according to the genomic and transcriptomic data of G. uralensis. Then, iTRAQ and LC-MS/MS were applied to detect significant protein changes between cultivated and wild G. uralensis. A total of 2751 validated proteins were obtained with high confidence, and 333 were differentially expressed. Differentially expressed proteins were identified and analysed by GO, KEGG, and STRING for network and pathway enrichment. Ultimately, we combined the iTRAQ results with our previous investigation on metabolites to understand the molecular mechanisms underlying metabolite accumulation. Results: The results showed that differentially expressed proteins were mainly involved in the anabolism of carbohydrates and important amino acids that participate in primary metabolism and secondary metabolite synthesis. Another important pathway is the synthesis of flavonoids, which are generally accepted as important bioactive constituents of G. uralensis, and the accumulation of flavonoids in different synthesis stages in two ecotypes of G. uralensis was diverse. Therefore, the differentially abundant proteins in wild and cultivated G. uralensis possibly resulted in differences in medicinal compounds. Conclusion: Our study will provide novel clues for revealing the molecular mechanism of secondary metabolite synthesis as well as quality formation in wild and cultivated G. uralensis.