Comparative physiological responses and transcriptome analysis revealing the metabolic regulatory mechanism of Prunella vulgaris L. induced by exogenous application of hydrogen peroxide

Prunella vulgaris L. (Lamiaceae) is an important medicinal plant used in Northeast Asia, the Middle East and Europe and is now widely used in medicine, beverages and ornamentation. Phenolic acids, flavonoids and triterpene acids are the main bioactive compounds of P. vulgaris. Previous studies have confirmed that hydrogen peroxide (H2O2) plays a crucial role in promoting P. vulgaris phenolic acid, flavonoid, and triterpene acid biosynthesis. However, little is known about the molecular and biochemical mechanisms of the H2O2 signalling pathway. In the present study, physiological analysis showed that 2.0 mM exogenous H2O2 pretreatment activated oxidative stress in P. vulgaris plants. The photosynthetic capacity could be improved by increasing the photosynthetic pigment content and net photosynthetic rate under H2O2 stress in P. vulgaris. P. vulgaris also enhanced oxidation tolerance by mediating antioxidant systems and osmotic regulatory substances. P. vulgaris pretreated with H2O2 had higher jasmonic acid (JA) and salicylic acid (SA) but lower indole-3-acetic acid (IAA) accumulation in leaves. A total of 3474 differentially expressed genes (DEGs) were screened out from control and H2O2-pretreated P. vulgaris leaves by RNA-Seq analysis. Further analysis of these DEGs showed that H2O2 regulated the expression of metabolism-related genes of phytohormones, carbon, amino acid biosynthesis, and secondary metabolites. In addition, the H2O2 burst triggered JA and SA accumulation to promote phenolic acid, flavonoid, and triterpene acid biosynthesis by activating the expression of phytohormone and secondary metabolite-related genes. Furthermore, analysis of transcription factor (TF) expression indicated that H2O2 might impact P. vulgaris secondary metabolite biosynthesis through the regulation of bHLH, WRKY, and MYB TFs. This study provides important information on the metabolic regulatory mechanisms by which exogenous H2O2 influences secondary metabolite production in P. vulgaris.