Versatility in acyltransferase activity completes chicoric acid biosynthesis in purple coneflower

Abstract

Purple coneflower (Echinacea purpurea (L.) Moench) is a popular native North American herbal plant. Its major bioactive compound, chicoric acid, is reported to have various potential physiological functions, but little is known about its biosynthesis. Here, taking an activity-guided approach, we identify two cytosolic BAHD acyltransferases that form two intermediates, caftaric acid and chlorogenic acid. Surprisingly, a unique serine carboxypeptidase-like acyltransferase uses chlorogenic acid as its acyl donor and caftaric acid as its acyl acceptor to produce chicoric acid in vacuoles, which has evolved its acyl donor specificity from the better-known 1-O-β-D-glucose esters typical for this specific type of acyltransferase to chlorogenic acid. This unusual pathway seems unique to Echinacea species suggesting convergent evolution of chicoric acid biosynthesis. Using these identified acyltransferases, we have reconstituted chicoric acid biosynthesis in tobacco. Our results emphasize the flexibility of acyltransferases and their roles in the evolution of specialized metabolism in plants.

Systematic identification and expression profiles of the BAHD superfamily acyltransferases in barley (Hordeum vulgare)

“…It has also shown potential reversal effect in antitumor adjuvant therapy 6 . The formation of chicory acid in echinacea also involves BAHD acyltransferase; this metabolite has high medicinal value in antiviral, anti-inflammatory, and glycolipid balance 7 .…”

Synthetic biology of plant natural products: From pathway elucidation to engineered biosynthesis in plant cells

“…At present, the main approach for functional verification of target pathways in their original plants is to inhibit the function of all or part of the enzymes by gene deletion or expression silencing and then to detect changes in secondary metabolites in order to identify the functions of candidate pathway genes. Gene expression silencing technology is a widely used reverse genetics method that can verify the function of plant genes ( Winzer et al., 2012 ; Kamthan et al., 2015 ; Qua et al., 2015 ; Zhao et al., 2015 , 2016 ; Ma et al., 2016 ; Fu et al., 2021 ). Qua et al.…”

“…(2015 ) used virus-induced gene silencing technology to rapidly identify a cytochrome P450 and an alcohol dehydrogenase that completed the pathway from tabersonine to the anti-cancer drug precursor vindoline. Fu et al. (2021 ) completed chicoric acid biosynthesis in purple coneflower through RNA interference technology for the identification of acyltransferase.…”

Substrate promiscuity of acyltransferases contributes to the diversity of hydroxycinnamic acid derivatives in purple coneflower

“…Three acyltransferases belonging to the BAHD family, namely hydroxycinnamoyl‐CoA:shikimate/quinate hydroxycinnamoyl transferase (EpHCT), hydroxycinnamoyl‐CoA:tartaric acid hydroxycinnamoyl transferase (EpHTT), and hydroxycinnamoyl‐CoA:quinate hydroxycinnamoyl transferase (EpHQT), catalyze the production of caffeoyl‐CoA, caftaric acid (caffeoyl tartaric acid), and chlorogenic acid (caffeoyl quinic acid), respectively. Subsequently, chicoric acid synthase (EpCAS) from the serine carboxypeptidase‐like (SCPL) family uses chlorogenic acid as acyl donor and caftaric acid as acyl acceptor to produce chicoric acid (Fu et al., 2021).…”

“…The CoA esters produced by 4‐coumarate:CoA ligase can be used by many BAHDs for the decoration of secondary metabolites, such as HCT/HQT (Niggeweg et al., 2004, Sonnante et al., 2010, Kriegshauser et al., 2021), rosmarinic acid synthase (Landmann et al., 2011), anthocyanin acyltransferases (Luo et al., 2007), and others (Bontpart et al., 2015). Not unexpectedly, EpBAHDs show substrate promiscuity regarding donor and acceptor and result in the biosynthesis of various simple HADs (Fu et al., 2021). EpCAS uses chlorogenic acid as an acyl donor rather than the known 1‐ O ‐β‐glucose esters, indicating the undergoing evolutionary change of SCPL acyltransferases (Ciarkowska et al., 2018).…”