Abstract：Expansins are considered to be the key regulators of cell wall extension during plant growth. In the present study, rapid amplification of cDNA(RACE) ends was used to clone the full length cDNA of TaEXPB8 homeologous genes. Four distinct cDNA sequences, with the length of 1180， 1169， 1150 and 1135 bp were identified and named as TaEXPB8-1， TaEXPB8-2， TaEXPB8-3 and TaEXPB8-4, respectively. Interestingly, putative auxin responsive cis-acting regulatory elements were detected in the promoter region of these four homeologous genes. Further analysis revealed that the chromosome location of TaEXPB8-1 was anonymous. but TaEXPB8-4 was located on Bin6DS（0.99~1.00）. Moreover, TaEXPB8-2 and TaEXPB8-3 were located on same chromosome region Bin6AS（0.35~1.00）, and tandem repeat of expansin genes were also detected in the linear genomic region of rice（Oryzasativa L.）, maize（Zea mays L.） and Arabidopsis. Thus, TaEXPB8-2 and TaEXPB8-3 could be originated from one ancestor gene, suggesting the possibility that these two genes were formed in wheat before the divergence of monocots and dicots. It was shown that TaEXPB8 gene was mainly expressed in elongation zone of wheat primary root, and down-regulated by high concentrations of exogenous auxin treatment, indicating that this gene it might play an important role in wheat root development, especially for root elongation.
