Diversity in a plant defense locus in wild barley populations is strongly correlated with water availability

Wild barley (Hordeum spontaneum) represents a significant genetic resource for crop improvement in barley (Hordeum vulgare) and for the study of the evolution and domestication of plant populations. The Isa gene from barley has a putative role in plant defense. We identified 16 Single Nucleotide Polymorphisms (SNPs) in the coding region of the Isa locus of 189 wild barley accessions from 8 sites that were characterized for 16 ecogeographical variables. The pattern of SNPs suggested a large number of recombination events within this gene and 7 amino acid substitutions were present in the coding region. Highly significant correlations were found between diversity at the Isa locus and key water variables - evaporation, rainfall, humidity and latitude. The association is evident at both a local and regional level. These results are consistent with the possibility that inhibition of the plant’s own α-amylase by BASI (isa encoded protein) may be a novel plant defense function. Study of the promoter and coding region of this gene indicate evolution of function at both levels.