Molecular cloning and functional characterization of chalcone isomerase from Carthamus tinctorius

Flavonoid is one of the widespread groups of plant secondary metabolites that provide several health benefits. However, the explicit mechanism of flavonoid biosynthesis in plants largely remains unclear. Chalcone isomerase an important class of enzyme presents crucial role during flavonoid metabolism in many plants. Here, we isolated the full-length cDNA (1161 bp) of a novel Chalcone Isomerase from safflower encoding 217 amino acid polypeptide using oligos from 5' and 3' ends. The result of Sanger sequencing and phylogenetic analysis revealed that CtCHI is highly homologous to other plants, including typical polyadenylation signals AATAA and Poly A tail. The transient expression in tobacco mesophyll cells using Green Fluorescent Protein tagging determined the subcellular localization of CtCHI in cell membrane and nucleus. The CtCHI ectopic expression in different safflower varieties at different flowering stages showed that CtCHI were found in abundance at the bud stage of Jihong No. 1. Further correlation analysis between CtCHI expression and flavonoid accumulation at various flowering phases suggested that CtCHI might play a potential role during flavonoid biosynthesis in safflower. In addition, the overexpression of pBASTA-CtCHI in transgenic Arabidopsis infiltrated with floral dip transformation showed relatively higher expression level and increased flavonoid accumulation than wild type. Moreover, the in vitro enzymatic activity and HPLC analysis of transgenic Arabidopsis confirmed the de novo biosynthesis of Rutin. Taken together, our findings laid the foundation of identifying an important gene that might influence flavonoid metabolism in safflower.