Assembly and Comparative Analysis of the Complete Mitochondrial Genome of Bromus inermis

Background: Bromus inermis is a high-quality perennial forage grass in the Poaceae family, with significant ecological and economic value. While its chloroplast genome has been sequenced, the mitochondrial genome of this species remains poorly understood due to the inherent complexity and frequent recombination of plant mitochondrial genomes. Methods: We sequenced the complete mitochondrial genome of B. inermis using both Illumina Novaseq6000 and Oxford Nanopore PromethION platforms. Subsequently, comprehensive bioinformatics analyses were performed, including genome assembly and annotation, repetitive sequence identification, codon usage analysis, RNA editing site prediction, the detection of chloroplast-derived sequences, and phylogenetic reconstruction. Results: The mitochondrial genome of B. inermis was determined to be 515,056 bp in length, with a GC content of 44.34%, similar to other Poaceae species. This genome encodes 35 protein-coding genes, 22 tRNA genes, and 10 rRNA genes. Repetitive sequences account for 16.2% of the genome, totaling 83,528 bp, including 124 simple sequence repeats, 293 dispersed repeats, and 31 tandem repeats. A total of 460 RNA editing sites were identified, among which 430 were nonsynonymous. Additionally, 110 putative chloroplast-derived sequences were detected. A phylogenetic analysis based on mitochondrial genome data clarified the species' evolutionary position within Poaceae. Conclusions: This study provides genetic resources for evolutionary research on and the communication of organelle genomes. Meanwhile, it also lays a solid foundation for the better development and utilization of the germplasm resources of B. inermis.