Abstract: With homologous cloning and RACE technology，ent-Kaurene oxidase（KO），a key enzyme in the pathway of gibberellins biosynthesis，was cloned from the shoot tip of‘Deltastal’（Cucumis sativus L.）and named CKO（GenBank accession number：JN792591）. The full cDNA was 1 895 bp in length with an open reading frame（ORF）encoding a protein of 519 amino acids. The protein molecular weight and isoelectric point were predicted to be 59.211 kD and 8.45 respectively. Amino acids homology analysis indicated that the sequence had 84% similarity with that of Momordica charantia. Sequence analysis showed that CKO belonged to cytochrome P450 superfamily and contained cysteine hemeiron ligand signature（FXXGXRXCXG）and transmembrane region. The fluorescent quantitative RT-PCR result showed that the expression level of CKO was the highest in leggy seedling under shading treatment，being 5.18 times of the normal one. While the expression of CKO significantly reducedafter spraying paclobutrazol at shading.

Key words: cucumber, ent-kaurene oxidase, gene, cloning, expression analysis