Abstract: GA20-oxidase is a critical enzyme in the pathway of gibberellins biosynthesis. In this
research，a GA20-oxidase gene in Malus，designated as MdGA20ox1(GenBank accession number：
KC493633)，was isolated from the apical tissue of apple rootstock SH40[（Malus × domestica）× M.
honanensis] by RT-PCR and RACE method. The length of full cDNA was 1 579 bp，containing a complete
open reading frame that encoding 392 amino acids. Amino acid sequence analysis revealed that the
sequence of MdGA20ox1 had 55.9%–96.7% identities with the sequence of GA20ox from plants such as
Zea mays，Arabidopasis thaliana，Pyrus communis and so on. Subcellular localization showed that the
MdGA20ox1 protein was located in the nucleus and the plasma membrane. The expression of MdGA20ox1
in SH28，SH40 and M26 showed a trend of decline-rise-decline，which were corresponded with the growing periods of their own-rooted seedlings. The expression of MdGA20ox1 and growth increment of
SH28 grafted cultivar‘Gala’were the highest of them，M26 grafted cultivar‘Gala’were higher than the
SH40 grafted cultivar‘Gala’. And the expression intensity of the MdGA20ox1 gene was negatively
associated to the dwarfing degree of the different rootstocks. The trend of expression of MdGA20ox1 gene
was the same in SH40 and SH28 grafted cultivar‘Gala’. The expression of MdGA20ox1 gene in the apical
tissue，young leaf，leaf and branch bark of semi-dwarf type SH28 grafted cultivar‘Gala’were higher than
dwarf type SH40 grafted cultivar‘Gala’.

Key words: apple, rootstock, MdGA20ox1, cloning, expression, subcellular location