Analysis of biosynthetic genes of phenolamides in Ricinus communis L. based on metabolomics and transcriptomes

Ricinus communis L., a medicinal plant widely distributed in tropical regions, is recognized not only for its use in traditional medicine but also for its antioxidant and other bioactive properties, which are largely associated with phenolamides. But the biosynthetic pathways of phenolamides in castor remain inadequately characterized. An integrated metabolomic and transcriptomic study was conducted to investigate the biosynthesis of phenolamides in root, stem, and leaf tissues at three time points (06:00, 12:00, and 18:00). The findings revealed that N-feruloyl putrescine was the predominant phenolamide, exhibiting peak accumulation in root tissues at 06:00. Integrated omics analysis and subsequent in vitro enzymatic assays led to the identification and functional characterization of two novel BAHD hydroxycinnamoyl transferase, RcHCT1 and RcHCT2 . And RcHCT1 displayed broad substrate specificity, catalyzing the formation of N-feruloyl putrescine, N-caffeoyl putrescine, p-coumaroyl putrescine, N-caffeoyl serotonin, and N-feruloyl agmatine from the corresponding substrates: putrescine, serotonin, and agmatine. In contrast, RcHCT2 exhibited narrower catalytic activity, producing only N-feruloyl putrescine and N-caffeoyl serotonin from putrescine and serotonin. Expression of both genes was also highest in roots at 06:00. And subcellular localization of RcHCT1 and RcHCT2 indicates that both proteins were localized to both the nucleus and the cytoplasm. In addition, the active pockets of RcHCT1 and RcHCT2 binding to different substrates, as well as adjacent amino acid residues, were excavated through molecular docking models. In conclusion, these findings provide critical insights into the biosynthetic pathway of phenolamides in castor, opening new avenues for its utilization in the design of bioactive molecules.