Systematic characterization of gene families and functional analysis of PvRAS3 and PvRAS4 involved in rosmarinic acid biosynthesis in Prunella vulgaris

Prunella vulgaris is an important material for Chinese medicines with rosmarinic acid (RA) as its index component. Based on the chromosome-level genome assembly we obtained recently, 51 RA biosynthesis-related genes were identified. Sequence feature, gene expression pattern and phylogenetic relationship analyses showed that 17 of them could be involved in RA biosynthesis. In vitro enzymatic assay showed that PvRAS3 catalyzed the condensation of p-coumaroyl-CoA and caffeoyl-CoA with pHPL and DHPL. Its affinity toward p-coumaroyl-CoA was higher than caffeoyl-CoA. PvRAS4 catalyzed the condensation of p-coumaroyl-CoA with pHPL and DHPL. Its affinity toward p-coumaroyl-CoA was lower than PvRAS3. UPLC and LC-MS/MS analyses showed the existence of RA, 4-coumaroyl-3',4'-dihydroxyphenyllactic acid, 4-coumaroyl-4'-hydroxyphenyllactic acid and caffeoyl-4'-hydroxyphenyllactic acid in P. vulgaris. Generation and analysis of pvras3 homozygous mutants showed significant decrease of RA, 4-coumaroyl-3',4'-dihydroxyphenyllactic acid, 4-coumaroyl-4'-hydroxyphenyllactic acid and caffeoyl-4'-hydroxyphenyllactic acid and significant increase of DHPL and pHPL. It suggests that PvRAS3 is the main enzyme catalyzing the condensation of acyl donors and acceptors during RA biosynthesis. The role of PvRAS4 appears minor. The results provide significant information for quality control of P. vulgaris medicinal materials.

Analysing a Group of Homologous BAHD Enzymes Provides Insights into the Evolutionary Transition of Rosmarinic Acid Synthases from Hydroxycinnamoyl-CoA:Shikimate/Quinate Hydroxycinnamoyl Transferases

The interplay of various enzymes and compounds gives rise to the intricate secondary metabolic networks observed today. However, the current understanding of their formation and expansion remains limited. BAHD acyltransferases play important roles in the biosynthesis of numerous significant secondary metabolites. In plants, they are widely distributed and exhibit a diverse range of activities. Among them, rosmarinic acid synthase (RAS) and hydroxycinnamoyl-CoA:shikimate/quinate hydroxycinnamoyl transferase (HCT) have gained significant recognition and have been extensively investigated as prominent members of the BAHD acyltransferase family. Here, we conducted a comprehensive study on a unique group of RAS homologous enzymes in Mentha longifolia that display both catalytic activities and molecular features similar to HCT and Lamiaceae RAS. Subsequent phylogenetic and comparative genome analyses revealed their derivation from expansion events within the HCT gene family, indicating their potential as collateral branches along the evolutionary trajectory, leading to Lamiaceae RAS while still retaining certain ancestral vestiges. This discovery provides more detailed insights into the evolution from HCT to RAS. Our collective findings indicate that gene duplication is the driving force behind the observed evolutionary pattern in plant-specialized enzymes, which probably originated from ancestral enzyme promiscuity and were subsequently shaped by principles of biological adaptation.