Functional divergence of tandem duplicate SCPL acyltransferase genes reveals convergent evolution of chicoric acid biosynthesis

Chicoric acid, a caffeic acid derivative exhibiting diverse bioactivities, has been identified in more than 60 plant species. Here we report an alternative biosynthetic pathway in lettuce ( Lactuca sativa ). BAHD acyltransferases catalyze the synthesis of chlorogenic acid, which serves as the acyl donor for four serine carboxypeptidase-like (SCPL) acyltransferases (LsSCPL1-4) encoded by tandemly duplicated genes. LsSCPL2 and LsSCPL4 catalyze the synthesis of chicoric acid using caftaric acid as the acyl acceptor. In contrast to the BAHD acyltransferases found in Echinacea species, LsSCPL1 and LsSCPL3 alter their substrate preferences through key amino acid substitutions and use tartaric acid as the acyl acceptor to synthesize caftaric acid. These tandemly duplicated SCPL genes are observed across several evolutionarily related species within the tribe Cichorieae. These findings illustrate the convergent evolution of chicoric acid biosynthesis in Asteraceae and highlight the complexity of acyltransferase activity in specialized metabolism in plants.