Highly conserved sequence of ClPKS11 encodes a novel polyketide synthase involved in curcumin biosynthesis in turmeric (Curcuma longa L.)

Abstract In order to elucidate a gene regulation model for biosynthesis of the major pharmaceutical compound curcumin in turmeric ( Curcuma longa ), a precise knowledge of sequence diversity and expression patterns of key genes of the pathway is necessary. Polyketide synthases (PKS) being the key enzymes involved in the 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 developmental stages, environmental conditions and management practices was analyzed. The full length cDNA of a novel PKS , showing higher transcript abundance and significant correlation with curcumin content was amplified and bioinformatic analysis was carried out. The present study could mine 63 transcripts of PKS from Curcuma transcriptome and among them, a novel transcript ( ClPKS11 ) showed 69 fold higher expression in a high curcumin variety. The expression of ClPKS11 correlated with curcumin content under different experimental conditions. It contained an open reading frame of 1176 bp, encoding a polypeptide of 391 amino acids with a predicted molecular mass of 42.9 kDa. CLPKS11 showed maximum identity of 72% with CURS3 (curcumin synthase 3) and exhibited amino acid differences in the substrate binding pocket, cyclization pocket and geometry shapers surrounding the active site. Molecular docking studies indicated a high substrate affinity for CLPKS11. Intrinsic levels of ClPKS11 may be used as a marker for screening for curcumin, as it shows divergent expressions in high and low curcumin genotypes that are detectable even at the very early developmental stage. The present study also laid the foundation for over expression of ClPKS11 in turmeric to investigate its physiological role in curcumin biosynthesis.