Molecular cloning and characterization of a cDNA encoding cycloartenol synthase from Fritillaria thunbergii Miq

Fritillaria thunbergii Miq., known as the bulbous plants of the genus fritillaria, produces a large amount of sterols. Homology based polymerase chain reactions (PCRs) with degenerate primers designed from the conserved sequences among the known cycloartenol synthase (CAS) resulted in cloning of a CAS from the young leaves of F. thunbergii Miq. A putative cycloartenol synthase cDNA (FtCAS) consists of a 2271 bp open reading frame, which encodes for 756 amino acids. The deduced amino acid sequence shows 82% homology to cycloartenol synthases from Dioscorea zingiberensis. Heterologous expression of the FtCAS in the methylotrophic yeast, Pichia pastoris, resulted in production of cycloartenol. Our results indicate that FtCAS encode cycloartenol synthase.Key words: Fritillaria thunbergii Miq., cycloartenol synthase, cDNA cloning, 2,3-oxidosqualene cyclase.