Complete mitochondrial genome of Agropyron cristatum reveals gene transfer and RNA editing events

Abstract Background As an important forage in arid and semi-arid regions, Agropyron cristatumprovides livestock with exceptionally high nutritional value. Additionally, A. cristatum exhibits outstanding genetic characteristics to endure drought and disease. Therefore, rich genetic diversity serves as a cornerstone for the improvement of major food crops. The purposes of this study were to systematically describe mitogenome of A.cristatumand preliminarily analyze its internal variations. ResultThe A. cristatum mitogenome was a single-ring molecular structure of 381,065 bp that comprised 52 genes, including 35 protein-coding, 3 rRNA and 14 tRNA genes. Among these, two pseudoprotein-coding genes and multiple copies of tRNA genes were observed. A total of 320 repetitive sequences was found to cover more than 10% of the mitogenome (105 simple sequences, 185 dispersed and 30 tandem repeats), which led to a large number of fragment rearrangements in the mitogenome of A. cristatum. Leucine was the most frequent amino acid(n=1087,10.8%) in the protein-coding genes of A. cristatum mitogenome, and the highest usage codon was ATG(initiation codon). The number of A/T changes at the third base of the codon was much higher than that of G/C. Additionally, 81 RNA editing sites were predicted, which were considerably fewer than those reported in other plant mitogenomes. Most of the RNA editing site base positions were concentrated at the first and second condon bases, which were C to T transitions. Moreover, we identified 95 sequencce fragments (total length of 34，343bp) that were transferred from the chloroplast to mitochondria genes, introns, and intergenic regions. The stability of the tRNA genes was maintained during this process. Selection pressure analysis of 23 protein-coding genes shared by 15 Poaceae plants, showed that most genes were subjected to purifying selectionduring evolution, whereas rps4, cob, mttB, and ccmBunderwent positive selection in different plants. Finally, a phylogenetic tree was constructd based on 22 plant mitogenomes, which showed that Agropyronplants have a high degree of independent heritability in Triticeae. ConclusionThe findings of this study provide new data for a better understanding of A. cristatum genes, and demonstrate that mitogenomes are suitable for the study of plant classifications, such as those of Agropyron. Moreover, it provides a reference for further exploration of the phylogenetic relationships within Agropyron species, and establishes a theoretical basis for the subsequent development and utilization of A. cristatum plant germplasm resources.