Evolutionary genetics of wheat mitochondrial genomes

The Triticum-Aegilopscomplex provides ideal models for the study of polyploidization, and mitochondrial genomes (mtDNA) can be used to trace cytoplasmic inheritance and energy production following polyploidization. In this study, gapless mitochondrial genomes for 19 accessions of five Triticumor Aegilopsspecies were assembled. Comparative genomics confirmed that the BB-genome progenitor donated mtDNA to tetraploid T. turgidum(genome formula AABB), and that this mtDNA was then passed on to the hexaploid T. aestivum(AABBDD). T urartu(AA) was the paternal parent of T. timopheevii(AAGG), and an earlier Ae. tauschii(DD) was the maternal parent of Ae. cylindrica(CCDD). Genic sequences were highly conserved within species, but frequent rearrangements and nuclear or chloroplast DNA insertions occurred during speciation. Four highly variable mitochondrial genes (atp6, cob, nad6, and nad9) were established as marker genes for Triticumand Aegilopsspecies identification. The BB/GG-specific atp6and cobgenes, which were imported from the nuclear genome, could facilitate identification of their diploid progenitors. Genic haplotypes and repeat-sequence patterns indicated that BB was much closer to GG than to Ae. speltoides(SS). These findings provide novel insights into the polyploid evolution of the Triticum/Aegilopscomplex from the perspective of mtDNA, advancing understanding of energy supply and adaptation in wheat species.