Abstract：α-amylase is not only involved in plant sugar metabolism and biological energy transfer, but also associates with the stress resistance of plants. The aim of this study was to clone the Bn-α-amylase gene, analyze the gene sequence and the gene expression pattern. The full-length coding sequence of Bn-α-amylase gene was cloned by RT-PCR methods, based on the sequence of Unigene4746 in the transcriptome library of ramie(Boehmeria nivea). Then the sequence was analyzed using bioinformatics methods. And the expression patterns of Bn-α-amylase in various ramie tissues or under different stress conditions were analyzed by Real-time PCR. The full-length coding sequence of Bn-α-amylase was 2 295 bp(GenBank accession no.KF860891). The encoded protein contained 765 amino acids, whose predicted pI was 5.685 and molecular weight was 86.11 kD. Bioinformatics analysis demonstrated that two conserved domain located in the carboxyl terminal, Subcellular localization prediction showed that the protein was located in the cytoplasm, there was no signal peptide and Transmembrane domain, the protein sequence was highly identical to α-amylase of other species. Bioinformatics analysis demonstrated that the sequence was highly identical to α-amylase of other species. It shared a 80% nucleotide identity to Malus × domestic, 76% to Arabidopsis thaliana and to Actinidia chinensis, 73% to Ricinus communis, and 67% to Glycine max. And it also shared the high protein similarity to these species with the valure of 68%, 65%, 65%, 69% and 51%, respectively. Phylogenetic tree analysis showed that the α-amylase of Glycine max, Vitis vinifera, Actinidia chinensis and Ricinus communis was closer to Bn-α-amylase than the α-amylase of Arabidopsis thaliana, Oryza sativa and Sorghum vulgare, then the α-amylase of Selaginella tamariscina was less closer to to Bn-α-amylase than the α-amylase of Arabidopsis thaliana, Oryza sativa, Sorghum vulgare. The results of Real-time PCR analysis suggested that Bn-α-amylase expressed in root, bark, stem xylem, stem apex and leaves, with a highest level in leaves, while a lowest level in root. Interestingly, the expression of Bn-α-amylase could be strongly induced by high salt or drought stress, while down regulated by ABA treatment. These results indicate that the Bn-α-amylase may play a role in ramie stress torlerance.
