Cell 162, 527–539 (2015)

Domestication of barley in the Near East involved converting the brittle rachis of wild plants to cultivars with non-brittle rachis that retain rather than disperse mature grains. Two tightly linked loci, Btr1 and Btr2, are known to account for the brittle rachis phenotype but little is known about the specific genes involved. Mohammad Pourkheirandish et al. now identify two alleles that confer the non-brittle rachis produced during two spatially and temporally independent domestication events.

Using fine mapping, sequence analyses and transformation experiments, the researchers identified and validated two genes on chromosome 3H controlling brittleness. The recessive btr1 allele contains a 1-bp deletion while the btr2 allele has lost an 11-bp segment. Mutant analysis showed that Btr1 regulates brittleness by affecting the thickness of cell walls and Btr2 by affecting the disarticulation cell layer.

A survey of a large panel of wild barleys and cultivars showed that the two alleles, btr1 and btr2, were retained after domestication and the non-brittle trait in all cultivars can be explained by either allele. In cultivars with only one non-brittle allele, low nucleotide diversity indicates that they were selected independently. The btr1-type emerged first by domestication from wild barley in south Levant, while the btr2-type was domesticated more recently further north.