Abstract: ‘Zhongai 1’is a pear dwarfing rootstock selected from the open pollinated seedlings of ‘Jinxiang’. One gene with 1 239 bp was obtained from the new shoot phloem of‘Zhongai 1’and ‘Jinxiang’and it was designated as PcAHS. PcAHS had no difference in sequence between the two varieties and it encoded 412 amino acids which had a sequence identity from 67% to 99% with the AHS gene in Malus × domestica（np_001280772.1），Prunus mume（XP_008242099. 1），Populous trichocarpa （XP_002306421.2）and Fragaria vesca（xp_00428771.1）. The expression of PcAHS gene in new shootphloem of‘Zhongai 1’was lower than that in its female parent‘Jinxiang’during the shoot growing stage，so we speculated that there may be difference in their promoter sequences. The promoter sequences of PcAHS gene isolated from‘Zhongai 1’and‘Jinxiang’had 828 bp and 888 bp respectively and the sequence identity was 89.1%. Sequence analysis showed that there is a deletion fragment of 58 bp（–496 bp to –553 bp）from PcAHS gene promoter sequence in‘Zhongai 1’. According to PLACE and PLANTCARE online database analysis，PcAHS gene promoter sequence of‘Zhongai 1’contained a particular BPBF transcription factor binding element P-box which was absent in‘Jinxiang’. So we speculated that fragment deletion and the particular transcription factor binding element P-box may be the cause of low expression of the gene and then influence auxin transport，eventually lead to dwarf.

Key words: pear, dwarfing rootstock, auxin hydrogen symporter gene, promoter, clone