Molecular cloning and expression profile analysis of three sunflower (Helianthus annuus) diterpene synthase genes

ent-Kaurene, a key precursor of gibberellins, is formed by the action of two diterpene synthases (diTPSs), ent-copalyl diphosphate synthase (CPS), and ent-kaurene synthase (KS). The full-length cDNAs of CPS- (HaCPS1L) and KS-like (HaKS2L and HaKS3L) genes were isolated from sunflower. The amino acid sequences of HaCPS1L, HaKS2L, and HaKS3L exhibit structural features and homology to diTPSs of several plant species involved in gibberellin biosynthesis. RT-PCR analysis indicates that the expression of all genes (HaCPS1L, HaKS2L, and HaKS3L) is highly regulated during growth and development. All three diTPSs are preferentially expressed in rapidly growing tissues. HaKS2L is expressed at a much lower level than the other two diTPS genes. During seed development, the high level of both HaCPS1L and HaKS3L transcripts correlated with the period of rapid growth of the embryo. The three diTPS genes are not subjected to feedback regulation by gibberellin activity.