Genome-wide analysis of the caffeic acid O-methyltransferase gene family reveal the role of PnCOMT1 in phytomelatonin biosynthesis and biotic stress tolerance in Panax notoginseng

Panax notoginseng , a traditional Chinese herbal medicine, is renowned for its rich and diverse triterpenoid saponins. P. notoginseng is extremely vulnerable to pathogens during cultivation due to its unique growth conditions. Phytomelatonin (N-acetyl-5-methoxytryptamine, MT), a ubiquitous signaling molecule essential for plant biotic resistance, is catalyzed by Caffeic acid O-methyltransferase (COMT) from N-acetyl-serotonin in the cytoplasm. However, information on COMT with N-acetylserotonin O-methyltransferase (ASMT) activity was lacking in P. notoginseng . In this study, twelve putative PnCOMT genes were identified in P. notoginseng . Furthermore, its physiochemical characteristics, phylogenetic relationship, chromosomal distribution, gene collinearity and promoter cis -element were investigated. Among them, Pno01G002223.t1 ( PnCOMT1 ) was considered a potential MT biosynthesis gene based on its high similarity to AtCOMT1 , which is involved in MT biosynthesis in Arabidopsis thaliana . The PnCOMT1 protein is localized in the cytoplasm. Notably, P. notoginseng caffeic acid O-methyltransferase 1 ( PnCOMT1 ) showed a high transcript level after MT treatment and black blot disease infection. To further evaluate PnCOMT1 function in MT biosynthesis, we overexpressed or complemented the PnCOMT1 gene in the A. thaliana comt mutant and P. notoginseng callus. Overexpression/complementation of PnCOMT1 significantly increased the concentration of phytomelatonin in P. notoginseng callus and A. thaliana comt mutant. Furthermore, PnCOMT1 -overexpressing A. thaliana plant (PnCOMT1-OE) showed higher immunity-related genes expression and MAPK activity, and lower bacterial abundance after Pst DC3000/flg22 treatment compared with comt mutant and comt complemented ( comt/ PnCOMT1) plants, indicating that overexpression of PnCOMT1 increased the bacterial resistance of the transgenic Arabidopsis plants. Taken together, our results indicated that PnCOMT1 positively regulates biotic stress resistance via enhancement of endogenous phytomelatonin biosynthesis. • A total of 12 PnCOMT genes were identified in Panax notoginseng . • PnCOMT1 with AMST function showed a high transcript level after MT treatment and disease infection. • Overexpression of PnCOMT1 significantly increased concentration of phytomelatonin. • PnCOMT1 positively regulates biotic stress resistance via enhancement of endogenous phytomelatonin biosynthesis.