Abstract: Ent-kaurenoic acid oxidase（KAO）is a critical enzyme in the pathway of gibberellins
biosynthesis. In this research，specific primers were designed based on sequence information of apple
genome and a coding sequence of ent-kaurenoic acid oxidase gene was isolated from new shoot leaves of
pear dwarfing inter-stock‘Zhongai 1’by RT-PCR method. The sequence was 1 568 bp in length with an
open reading frame（ORF）encoding a protein of 503 amino acids. Molecular weight and isoelectric point
of the protein was 57.59 kD and 9.47，respectively. Amino acids homology analysis indicated that the
sequence shared 53.14%–98.61% similarity with other reported KAOs，and it had the typical functional
regions of cytochrome P450 superfamily proteins，so named the gene as PcKAO1，GenBank accession
number was KC153027.1. The other two PcKAO1 genes from control pear varieties‘Zaosu’（tall）and
‘Jinxiang’（semi-dwarf）also were isolated by the same method. Multiple sequence alignment showed
that the PcKAO1 sequence only had few nucleotide bases difference among three varieties，but their
encoding amino acids sequences were completely consistent. Half quantitative RT-PCR results showed that
PcKAO1 gene expressed in every tested organs of‘Zhongai 1’，and in the seeds and ovary it had the
highest expression. In all the growth periods except the initial growth period（10th May）the PcKAO1 gene
expression of new shoot leaves in‘Zhongai 1’was lower than in control varieties tall‘Zaosu’and
semi-dwarf‘Jinxiang’. In these periods the new shoot growth speed of‘Zhongai 1’was gradually slowed
and stopped growing.

Key words: pear, ent-kaurenoic acid oxidase gene（KAO）, gene expression, dwarf