Objective  To decipher the gene function, phytoalexin biosynthesis, and disease resistance mechanism of Dendrobium officinale (Do), the premnaspirodiene oxygenase gene (PO) was cloned and its expressions in the plant in various organs at different growth stages studied.

  Method  RACE-PCR and RT-PCR were employed to clone the full-length cDNA and ORF of DoPO. ProtParam was used for the physiochemical determination, BLAST P on the amino acid homology, and MEGA 6.0 for the phylogenetic tree construction. The expressions of DoPO in different organs at flowering stage as well as in leaves at growth stages were examined by qPCR.

  Result  The DoPO encoded 498 amino acids, 1 704 bp in length with an 1 497 bp ORF. The unstable protein had a molecular weight of 56.914 kDa belonging to the P450 superfamily. It was phylogenetically clustered in the same branch with Phalaenopsis equestris (XP 020571355) and Apostasia shenzhenica (PKA52400) and most closely related to P. equestris. The relative DoPO expression in the leaves was significantly higher than that in the stems, roots, or flowers at flowering stage (P＜0.01); and during a year, that in October significantly higher than that in either August or December (P＜0.01) and that in December significantly higher than in August (P＜0.05).

  Conclusion  The full-length cDNA of DoPO was successfully cloned. Its relative expression in leaf peaked in October and was highest in leaves among the organs at flowering stage.