Molecular cloning and differential expressions of two cDNA encoding Type III polyketide synthase in different tissues of Curcuma longa L

Type III polyketide synthase family of enzymes play an important role in the biosynthesis of flavonoids and a variety of plant polyphenols by condensing multiple acetyl units derived from malonyl Co–A to thioester linked starter molecules covalently bound in the PKS active site. Turmeric (Curucma longa L.) through diverse metabolic pathways produces a large number of metabolites, of which curcuminoids had gained much attention due to its immense pharmaceutical value. Recent identification of multiple curcuminoid synthases from turmeric lead us to look for additional Type III PKS from this plant. The current study describes the occurrence of a multigene family of Type III PKS enzymes in C. longa by RT-PCR based genomic screening. We have also isolated two new Type III PKS, ClPKS9 and ClPKS10 using homology based RT-PCR and data mining. The comparative sequence and phylogenetic analysis revealed that the two PKSs belong to different groups with only 56% sequence similarity at their amino acid level. ClPKS9 shows all possible sequence requirements for a typical chalcone synthase whereas ClPKS10 shows promising variation at amino acid level and high similarity to reported curcuminoid synthases. ClPKS9 and ClPKS10 exhibited distinct tissue specific expression pattern in C. longa with the ClPKS9 transcript abundant in shoot and rhizome than leaves whereas ClPKS10 transcript was found to be high in leaf and very low in rhizome and root. Therefore it was concluded that ClPKS9 and ClPKS10 may have divergent function in planta, with possible role in typical chalcone forming reaction and curcuminoid scaffold biosynthetic pathway respectively.

► Two novel and divergent Type III PKSs has been identified from Curcuma longa.
► Promising variation at catalytic residues and tissue specific expression patterns.
► ClPKS9 transcripts abundant on rhizome and ClPKS10 on leaves.
► Possible role of ClPKS9 in chalcone and ClPKS10 in curcuminoid biosynthesis.
► The work points towards possible curcuminoid biosynthesis in aerial parts.