Abstract：Beta-amylase (BAM) plays a central role in the complete degradation of starch tometabolisable or fermentable sugars during the germination or maltingof cereal grains. It was found to be involved in the abiotic stress responsesof crops. A genome-wide survey of BAM genes in 5 grass species was performed, including rice, maize, sorghum, Setaria, and Brachypodium, by describing their phylogenetic relationships, functional divergence, and adaptive evolution. The phylogeny classified the gramineous BAM genes into 10 clusters of orthologous genes (COGs), and the genes in the same COG shared the syntenic region. Functional divergence analysis provided statistical evidence that both the shift in the evolutionary rate pattern and cluster-specific alterations of amino acid physiochemical properties contributed to COG-specific functional evolution of BAM genes in grasses. In addition, 3 COGs were found to be influenced by positive selection through maximum likelihood analysis. The expression patterns of rice BAM genes were investigated, and the resultsrevealed that they were differentially expressed under the treatments of abiotic stresses. These observations may provide useful references for further functional detection of BAM genes in grasses.
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