[Cloning and application in synthetic biology of chalcone synthase gene from Lithocarpus litseifolius]

Lithocarpus litseifolius is rich in the chalcones phloridzin and trilobatin, the biosynthesis pathways of which have not been fully demonstrated. Chalcone synthase(CHS) is the first key rate-limiting enzyme in the biosynthesis of flavonoids in plants. To explore the functions of CHS gene family in chalcone synthesis of L. litseifolius, this study screened out two CHS genes(LlCHS1 and LlCHS2) from the transcriptome data of this plant, and then bioinformatics analysis and functional characterization were performed for the two genes. The bioinformatics analysis showed that LlCHS1 and LlCHS2 were acidic hydrophilic stable proteins with no transmembrane domain, composed of 395 and 390 amino acid residues, respectively. Both of them contained the characteristic amino acid sequence "WGVLFGFGPGL" and highly conserved active sites(Cys-164, Phe-215, His-303, and Asn-336) of the CHS family. The phylogenetic tree showed that LlCHS1 shared the same clade with similar genes in Aquilaria sinensis, and LlCHS2 was closely related to similar genes in Malus domestica. Under exogenous addition of phloretic acid, co-expression of LlCHS1 or LlCHS2 with Aa4CL from Aromatoleum aromaticum in Escherichia coli catalyzed the production of phloretin from phloretic acid. This study laid a theoretical foundation for revealing the functions of CHS in plants and provided new enzymatic modules for producing phloretin by synthetic biology.