Objective  The SQE genes of Dendrobium officinale associated with the key enzyme involving in the sterol biosynthesis, squalene monooxygenase, were cloned for bioinformatics analysis and determination of their expressions in the stems and leaves of the orchid plant at different growth stages.

  Method  The 3'RACE primers of DoSQE1 and DoSQE2 were designed based on SQE fragment with the 5' terminal from the transcriptome data of D. officinale. The full lengths cDNAs of DoSQE1 and DoSQE2 were cloned and a bioinformatics analysis carried out. Expressions of the genes in the stems and leaves in August, October and December were detected by qRT-PCR.

  Result  The full-length of DoSQE1 was 1 796bp (GenBank accession MT160182) containing an 1 554 bp ORF encoding 517 amino acids (aa) and that of DoSQE2 1 963 bp (GenBank accession MT160183) containing an 1 578 bp ORF encoding 525 aa. DoSQE1 had two transmembrane regions at 4–22 aa and 55–72 aa, while DoSQE2 had only one transmembrane region at 5–23 aa. DoSQE1 contained a squalene epoxidase domain at 204–476 aa, and DoSQE2 at 211–484 aa. The phylogenetic analysis showed DoSQE1 to be closely related to SQE of Phalaenopsis equestris (XP_020599860.1), and DoSQE2 to that of Phalaenopsis equestris (XP_020579136.1). Their gene expressions were detected in the stems as well as the leaves by qRT-PCR with the expression in the leaves significantly higher than that in the stems. And, the expression of DoSQE1 peaked in August, whereas, that of DoSQE2 in October.

  Conclusion  DoSQE1 and DoSQE2 were successfully cloned for the study that showed differences in their expressions. The information obtained would lead to further investigation on the biosynthesis mechanism and metabolic regulation of sterols in D. officinale.