Chicoric acid biosynthesis during seed germination provides purple coneflower with better allelochemical

Abstract

Known as a bioactive compound with various biological functions for plants and humans, chicoric acid is the major secondary metabolite presented in the whole plant of purple coneflower (Echinacea purpurea (L.) Moench). It is synthesized from caftaric acid and chlorogenic acid (5-caffeoyl quinic acid) by a special acyltransferase. Interestingly, the relative contents of chicoric acid and its two substrates in seeds were different from those of other tissues. The diversity mechanism of these chemicals and the underlying physiological significance remain unknown. Here, through a non-target metabolomic analysis, significant metabolic shifts, especially the dynamics of the contents of chicoric acid and its two substrates, were observed during the seed germination process. The contents of caftaric acid and chicoric acid kept on increasing after sprout, while chlorogenic acid decreased and converted to chicoric acid. Accordingly, the structural genes responsible for the biosynthesis of caftaric acid and chicoric acid were upregulated since sprout, just a little head of accumulation of chemicals. The upstream biosynthetic genes providing essential precursor caffeoyl CoA was also induced since sprout explain the increase of the sum of these compounds. Interestingly, during the seed germination process, chicoric acid was secreted into the culture medium and showed a more substantial growth inhibition effect on A. thaliana than its two substrates, indicating the significance of its biosynthesis. In summary, these results demonstrate the metabolic change and its biological meaning during the germination process of purple coneflower seeds.