Whole Genome Sequence of Aegilops sharonensis Reveals Inconsitency in the Sitopsis Section Taxonomy

Sharon goatgrass, Aegilops sharonensis, is a diploid relative of hexaploid bread wheat, Triticum aestivum (genomic constitution AABBDD), and a member of the Sitopsis section of Aegilops. Numerous studies have shown that the wheat A- and D-genomes originated from Triticum urartu (AA) and Aegilops tauschii (DD), respectively. However, the source of the B-genome has remained elusive or at best controversial with some studies pointing to members of the Sitopsis. We sequenced the genome of two accessions of Ae. sharonensis (S^shS^sh) and compared them to assemblies of the sequenced chromosome arms of hexaploid wheat and diploid relatives. Remarkably, Ae. sharonensis was found to be closely related to the D-genome and its progenitor, whereas Ae. speltoides (SS), another Sitopsis member, was found to be more closely related to the B-genome. We extended our analysis by sequencing the transcriptomes of 16 accessions that cover the natural habitat of Ae. sharonensis. All accessions have the same close relationship to the D-genome. Additionally, a high level of intraspecific variation was detected, suggesting that this species is prone to outcrossing. In summary, the Sitopsis classification is inconsistent with our genome-wide analysis of Ae. sharonensis, provoking a need to reconstruct the current taxonomy of Aegilops.