Abstract
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.
Highlights
Aegilops tauschii Cosson (DD, 2n = 2x = 14), which is the D genome progenitor of common bread wheat, is characterized by abundant genetic variation and is noted for its strong tillering ability and high plant tolerance
With respect to gene order, gene number, and inverted repeats (IRs)/SC boundary regions, we demonstrate that genomic structure is well conserved among the cp genomes of the 17 Ae. tauschii accessions we assembled using Illumina next-generation DNA sequencing technology
Intraspecific differences among the cp genomes were detected primarily in non-coding regions which are the main features contributing to the observed differences in genome size
Summary
Previous studies have proved that L2 lineage is involved in the origin of common wheat and is limited to a narrow area within the whole species’ overall distribution range (Wang et al, 2013; Dvorak et al, 2012), as well as L1 lineage is adapted to more diverse environments (Dudnikov, 2012). Given the large genetic distance between L1 and L2, it has been proposed that Ae. tauschii (especially L1 lineage) showes more genetic differentiation than does the D genome of the common wheat (Lubbers et al, 1991; Wang et al, 2013; Dvorak et al, 2012). In common with wild crop progenitors, Ae. tauschii, especially L1 lineage, is considered to represent a potentially valuable germplasm resource that could be exploited for genetic improvement of common wheat (Kilian et al, 2011; Zhang et al, 2017; Zhang et al, 2018). Owing to widely geographical distribution of the L1 lineage, studying of its genetic and evolutionary relationships contribute to more effective utilization of wild germplasm resources
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