Identification and mapping of genes related to caffeoylquinic acid synthesis in Cynara cardunculus L.

The caffeoylquinic acid (CQA) biosynthesis pathway in plants is not fully understood, but the BAHD superfamily, a large class of acyl-CoA-dependent acyltransferases, may represent an interesting group for the isolation of enzymes playing a key role. Globe artichoke (Cynara cardunculus var. scolymus) represents a relevant model species for studying CQA biosynthesis, because the plant accumulates high amounts and a diverse spectrum of CQAs in its leaves. An in silico scan of globe artichoke ESTs was based on a search string targeting the conserved motifs of BAHD proteins and complete BAHD sequences present in a range of species. EST hits were assembled into 32 unigenes and their phylogeny characterized. Among which were three putative BAHD acyltransferases showing a high level of similarity to globe artichoke HCT and HQT enzymes. The full-length cDNAs of these three proteins were isolated; two of these acyltransferases were able to synthesize both chlorogenic acid and p-coumaroylquinate, assessing their involvement in CQA biosynthesis. Upon exposure to UV-C radiation, which is known to induce CQA biosynthesis, expression of two of the enzyme transcripts was up-regulated while that of the third was unaffected. By analysing the globe artichoke unigene consensus sequences, further two genes (i.e. C4H, 4CL), related not only to flavonoids but also to chlorogenic acid (a mono-CQA) biosynthesis, were also identified and were genetically mapped along with the three acyltransferase genes. The research has improved the knowledge base surrounding globe artichoke BAHD members. The mapping of the genes related to the chlorogenic acid biosynthesis pathway may contribute to a greater understanding of the genetic basis of the synthesis of these compounds of nutraceutical and pharmaceutical value.