Highly conserved sequence of ClPKS11 encodes a novel polyketidesynthase involved in curcumin biosynthesis in turmeric (Curcumalonga L.)

Abstract

In order to elucidate a gene regulation model for biosynthesis of the major pharmaceutical compoundcurcumin in turmeric (Curcuma longa), a precise knowledge of sequence diversity and expression patternsof key genes of the pathway is necessary. Polyketide synthases (PKS) being the key enzymes involved inthe pathway, attempts were made to mine the major PKS from the transcriptome of the Curcuma rhizome.Comparative expression of candidate genes vis a vis curcumin content across accessions, various develop-mental stages, environmental conditions and management practices was analyzed. The full length cDNAof a novel PKS, showing higher transcript abundance and significant correlation with curcumin contentwas amplified and bioinformatic analysis was carried out. The present study could mine 63 transcriptsof PKS from Curcuma transcriptome and among them, a novel transcript (ClPKS11) showed 69 fold higherexpression in a high curcumin variety. The expression of ClPKS11 correlated with curcumin content underdifferent experimental conditions. It contained an open reading frame of 1176 bp, encoding a polypeptideof 391 amino acids with a predicted molecular mass of 42.9 kDa. CLPKS11 showed maximum identity of72% with CURS3 (curcumin synthase 3) and exhibited amino acid differences in the substrate bindingpocket, cyclization pocket and geometry shapers surrounding the active site. Molecular docking studiesindicated a high substrate affinity for CLPKS11. Intrinsic levels of ClPKS11 may be used as a marker forscreening for curcumin, as it shows divergent expressions in high and low curcumin genotypes that aredetectable even at the very early developmental stage. The present study also laid the foundation for overexpression of ClPKS11 in turmeric to investigate its physiological role in curcumin biosynthesis.