The D genome progenitor of bread wheat, Aegilops tauschii Cosson (DD, 2n = 2x = 14), which is naturally distributed in Central Eurasia, ranging from northern Syria and Turkey to western China, is considered a potential genetic resource for improving bread wheat. In this study, the chloroplast (cp) genomes of 17 Ae. tauschii accessions were reconstructed. The cp genome sizes ranged from 135,551 bp to 136,009 bp and contained a typical quadripartite structure of angiosperms. Within these genomes, we identified a total of 124 functional genes, including 82 protein-coding genes, 34 transfer RNA genes and eight ribosomal RNA genes, with 17 duplicated genes in the IRs. Although the comparative analysis revealed that the genomic structure (gene order, gene number and IR/SC boundary regions) is conserved, a few variant loci were detected, predominantly in the non-coding regions (intergenic spacer regions). The phylogenetic relationships determined based on the complete genome sequences were consistent with the hypothesis that Ae. tauschii populations in the Yellow River region of China originated in South Asia not Xinjiang province or Iran, which could contribute to more effective utilization of wild germplasm resources. Furthermore, we confirmed that Ae. tauschii was derived from monophyletic speciation rather than hybrid speciation at the cp genome level. We also identified four variable genomic regions, rpl32-trnL-UAG, ccsA-ndhD, rbcL-psaI and rps18-rpl20, showing high levels of nucleotide polymorphisms, which may accordingly prove useful as cpDNA markers in studying the intraspecific genetic structure and diversity of Ae. tauschii.
Peer Review #2 of "The complete chloroplast genomes of seventeen Aegilops tauschii: genome comparative analysis and phylogenetic inference (v0.1)"