Characterization of a highly conserved Antheraea pernyi spermidine synthase gene

In the present study, we isolated a spermidine synthase gene from Antheraea pernyi (ApSpds) using expressed sequence tag method. The obtained cDNA sequence of 1483 bp contains an open-reading frame of 864 bp encoding a polypeptide of 287 amino acids. Sequence analysis revealed that ApSpds belonged to class I of AdoMet-MTase family, and exhibited 30% identity to those from bacteria, 45-48% identity to fungi, 36-47% identity to plants, 52-54% identity to vertebrates and 53-80% identity to invertebrates. Phylogenetic analysis found that the used Spds protein sequences were well divided into five groups corresponding to bacteria, fungi, plants, invertebrates and vertebrates, respectively. These results further confirmed that Spds is highly conserved through evolution of life organisms. The ApSpds mRNA is expressed during all four developmental stages and is present in all examined tissues with the highest abundance in the muscle, in which the relative mRNA expression level was 1.6 times higher than in the fat body. Although not significant, the mRNA level decreased after high-temperature exposure suggesting that the Spds gene may not be involved in temperature stress tolerance in A. pernyi. Taken together, our results suggested that ApSpds play an important role in development of silkworm.