Abstract
Triticum turgidum
and
T. timopheevii
are two tetraploid wheat species sharing
T. urartu
as a common ancestor, and domesticated accessions from both of these allopolyploids exhibit nonbrittle rachis (i.e., nonshattering spikes). We previously described the loss-of-function mutations in the
Brittle Rachis 1
genes
BTR1-A
and
BTR1-B
in the A and B subgenomes, respectively, that are responsible for this most visible domestication trait in
T. turgidum
. Resequencing of a large panel of wild and domesticated
T. turgidum
accessions subsequently led to the identification of the two progenitor haplotypes of the
btr1-A
and
btr1-B
domesticated alleles. Here, we extended the haplotype analysis to other
T. turgidum
subspecies and to the
BTR1
homologues in the related
T. timopheevii
species. Our results showed that all the domesticated wheat subspecies within
T. turgidum
share common
BTR1-A
and
BTR1-B
haplotypes, confirming their common origin. In
T. timopheevii
, however, we identified a novel loss-of-function
btr1-A
allele underlying a partially brittle spike phenotype. This novel recessive allele appeared fixed within the pool of domesticated Timopheev’s wheat but was also carried by one wild
timopheevii
accession exhibiting partial brittleness. The promoter region for
BTR1-B
could not be amplified in any
T. timopheevii
accessions with any
T. turgidum
primer combination, exemplifying the gene-level distance between the two species. Altogether, our results support the concept of independent domestication processes for the two polyploid, wheat-related species.