Author(s): Samappito S, Page J, Schmidt J, De-Eknamkul W, Kutchan TM
Three cDNAs encoding very similar but unique isoforms of chalcone synthase (EC 22.214.171.124) were isolated from a cDNA library prepared from RNA from root tissue of the Thai medicinal plant Cassia alata L. (ringworm bush, Leguminosae). Gene transcript for these three type-III polyketide synthases was found to accumulate predominantly in roots. The heterologously expressed enzymes accepted acetyl-, n-butyryl-, isovaleryl-, n-hexanoyl-, benzoyl-, cinnamoyl-, and p-coumaroyl-CoA as starter molecules and together with the co-substrate malonyl-CoA, formed multiple products. With the exception of the assay in which acetyl-CoA was used as the starter molecule, all substrates yielded a phloroglucinol derivative resulting from three sequential condensations of acetate units derived from three malonyl-CoA decarboxylations. Every substrate tested also produced two pyrone derivatives, one resulting from two acetate unit condensations (a bis-noryangonin-type pyrone derailment product) and one resulting from three acetate unit condensations (a 4-coumaroyltriacetic acid lactone-type pyrone derailment). C. alata accumulates the flavonoids quercetin, naringenin and kaempferol in roots, suggesting that the in planta function of these enzymes is the biosynthesis of root flavonoids.
Referred From: https://link.springer.com/article/10.1007/s00425-002-0872-8
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