Chicoric acid provides better ultraviolet protection than the sum of its substrates in purple coneflower plants

Abstract

Plants live in complex environments and need to cope with various biotic and abiotic stresses. Plant secondary metabolites are not only medicines/supplements for humans but are also important weapons used by plants for defense. Chicoric acid is the main active ingredient and is a major secondary metabolite of purple coneflower (Echinacea purpurea (L.) Moench). A special acyl donor changed serine carboxypeptidase-like acyltransferase catalyzes chicoric acid biosynthesis from caftaric acid and chlorogenic acid. The biological role of chicoric acid in purple coneflower and the significance of its biosynthesis being catalyzed by an acyl donor changed acyltransferase remain unclear. In the present study, correlation analysis and various in vitro experiments were investigated. Chicoric acid contents among different purple coneflower accessions were found to be negatively correlated with latitude, which indicated a possible role in ultraviolet protection. Ultraviolet light induced oxidative stress in purple coneflower leaves and upregulation of chicoric acid biosynthetic genes. However, chicoric acid was consumed by reactive oxygen species to alleviate oxidative stress. Chicoric acid provided ultraviolet protection by acting as a sunscreen and antioxidant agent. Notably, chicoric acid exhibited stronger ultraviolet absorption and antioxidant activity than the sum of its two substrates, which indicated the significance of its biosynthesis by an acyl donor changed acyltransferase. This study also implied that low doses of ultraviolet light might be good elicitors for simulating chicoric acid biosynthesis in purple coneflower.