Characterization of Evolution and Tissue-Expression of Rice (Oryza sativa L.)α-Amylase Genes

α-amylases play an important role in starch degradation in plants, especially in cereal germinating seeds. Existing reports on structural organization and evolution of rice α-amylase family mainly focus on members of subfamilies OsAmyl and OsAmy3 and their expression in germinating seeds, however, it is not known whether the putative α-amylase genes else exist in rice genome and what their structural organization, evolution and expression profiling look like especially among subfamilies. Via TblastN search and conservative domain analysis, we revealed that there were 21 putative α-amylase genes in rice genome. Through tools of bioinformatics, phylogenetic reconstruction and semi-quantitative RT-PCR, we studied the structural evolution among these 11 α-amylase genes and their spatial-temporal expression profiling. The results showed that there was a distinctly divergent and ranked geae structure among members of this family. OsAmy5A and OsAmy4A were the most primitive genes, and other ones were evolved from them mainly through loss of introns and fixed more conserved domains and sequences. These genes were also divergent in expression and function. The more primitive the genes are the less spatial-temporal specificity in gene expression they have. OsAmy5A, OsAmy4A, and OsAmy2A were expressed in all tissues, however, the rest were expressed spatially and temporally. OsAmy1A, which was expressed at the beginning of seed germination but not all during the grain filling stage, should serve to control energy supply between generations. OsAmy3A, both expressed dramatically at the end of grain filling and the initiation of seed germination, should be related to sustaining life activities in embryos of dormancy seeds. OsAmy3D and OsAmy3E were regulated at the gene expression level by sugar concentration during seed germination, and may play an important role in stable and continuous energy supply during seed germination.