Abstract:To elucidate the function in growth and development of expansins in Eucalyptus, two expansin genes EgrEXPA8 and EgrEXPA10 were cloned based on differential expression genes in the transcriptome of transition from primary growth to secondary growth of E. grandis. EgrEXPA8 and EgrEXPA10 encoded 249 and 244 amino acids, respectively. EgrEXPA8 and EgrEXPA10 were hydrophilic proteins. However, the stability of EgrEXPA8 was higher than that of EgrEXPA10. qRT-PCR analysis showed that the expression of EgrEXPA8 and EgrEXPA10 were high in young leaves and stem apex, and low in xylem and phloem. The expression of them was high in stem apex at primary growth stage, and low in internode at secondary growth stage, indicating that the two genes might be mainly involved in primary growth or negative regulation of secondary growth in E. grandis. The expressions of EgrEXPA8 and EgrEXPA10 were inhibited under salt stress and methyl jasmonate treatment, but significantly up-regulated treated with salicylic acid, under boron and phosphorus deficiency. Therefore, it was suggested that EgrEXPA8 and EgrEXPA10 genes in E. grandis would play an important role in response to stress.