Assembly and comparative analysis of the complete mitochondrial genome of hexaploid oat (Avena sativa)

Common oat (Avena sativa) is a globally important hexaploid cereal crop with a large and complex genome. While its nuclear and chloroplast genomes have been extensively characterized, the mitochondrial genome of hexaploid oat has remained unresolved, limiting our understanding of organellar evolution and mitochondrial function in this polyploid species.

We report the first complete assembly and comprehensive analysis of the A. sativa mitochondrial genome, which comprises two circular chromosomes totaling 634,262 bp with a GC content of 44.11%. The mitogenome encodes 78 genes, including 37 protein-coding genes (PCGs), 27 tRNAs, 12 rRNAs, and 2 pseudogenes. Extensive repeat sequences were identified, providing a structural basis for recombination and genome plasticity. Codon usage analysis revealed a strong AT bias and distinct codon preferences, while Ka/Ks analysis indicated predominant purifying selection on core OXPHOS genes, with possible signals of positive selection in mttB and nad7. A total of 463 RNA editing sites were predicted, predominantly enhancing protein hydrophobicity and potentially optimizing mitochondrial function. Comparative analyses revealed high collinearity with the diploid oat A. longiglumis and frequent transfers of chloroplast-to-mitochondrial DNA. Phylogenetic reconstruction based on 32 conserved mitochondrial genes robustly resolved relationships within Poaceae and its relatives.

The first complete mitogenome of hexaploid oat provides new insights into mitochondrial genome structure, evolution, and organellar genome dynamics in polyploid species, and constitutes a valuable genomic resource for future studies of mitochondrial biology, comparative genomics, and marker development in oats.