Abstract: 【Objective】Aim of this research is to clone and investigate the expression of the expansin gene from new root of Malus hupehensis (Pamp) Rehd., which will be helpful to study the action of expansin gene in roots development. 【Method】With the RT-PCR and RACE methods, a full length cDNA sequence of expansin gene was cloned in root of Malus hupehensis (Pamp) Rehd. The expression of expansin gene was analysed by Northern blot【Result】Sequencing and structural analysis showed that the full-length of MhEXP1 consisted of 1111bp with an open reading frame of 771bps that could code for a protein of 257 amino acids.The predicted MW and PI were 27.8kD and 8.9. The polypeptide had a N-terminal signal peptide of 23 amino acids like many other expansins. Essential features of the protein such as the eight cysteine residues and four tryptophan residues near the C-terminal end are conserved in the sequence. The HFD sequence, which has been shown to be a part of the endoglucanase active site is also present in MhExp1. Northern blot showed that the expression of MhEXP1 gene was more significant in roots than in leaves. The transcriptional level of the MhEXP1 gene in the roots of Malus hupehensis (Pamp) Rehd was most highly by 10μmol/L IBA treatment for 6 h.【Conclusion】All of the results indicated that the obtained gene is a new member of expansin gene family. The transcription of MhEXP1 was regulated by IBA and it played an important role in the development of Malus hupehensis (Pamp) Rehd. roots.

Key words: M hupehensis Rehd. Var pingyiensis Jiang, Expansin, cDNA cloning, Sequence analysis and expression