Adaptive evolution of α-amylase genes in wild barley (Hordeum spontaneum) on micro and macro scales

Alpha-amylases play essential roles in germination, and the malting and brewing processes, by hydrolyzing starch granules present in the endosperm of barley. Hordeum spontaneum C. Koch, the progenitor of cultivated barley that harbors rich genetic diversity, was collected from seven different environments. To investigate the influence of microclimatic ecological divergence on α-amylase, single nucleotide polymorphisms (SNPs) in amy genes from these populations were determined. A total of 16 and 17 SNPs were detected in the coding sequences of amy1 and amy2, respectively, from the seven wild barley populations. Among these SNPs, three in amy1-2 and nine in amy2-2 were significantly associated with ecological factors. The genetic divergence of amy sequences was significantly different among the populations. Natural microclimatic selection was apparently the major evolutionary driving force causing interslope divergence and adaptive evolution of these genes. The genetic variation in amy1-2 and amy2-2 was at least partly ecologically determined in these populations, representing adaptive patterns generated by natural selection. The SNPs were apparently generated by natural selection in climatic environmental patterns at both the micro ("Evolution Canyon") and macro (across Israel, Galilee, and Negev) scales.