The complete mitochondrial genome and phylogenetic analysis of Festuca pratensis

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Abstract
Introduction: Festuca pratensis is a perennial herb of Festuca in Poaceae. It has become an important forage and ecological restoration grass species due to its strong stress resistance and high nutritional value. Limited by the complexity of the forage grasses genome, the number of mitochondrial genome assembly in this genus is limited, which seriously restricts the research process of early mitochondrial genome evolution and key gene mining. Methods: We assembled and annotated the first high-quality mitochondrial genome of Festuca pratensis using third-generation and second-generation sequencing technology. The genome structure, sequence characteristics, evolutionary selection pressure and genetic relationship of Festuca pratensis mitochondrial genome were analyzed. Results and discussion: The mitochondrial genome has a multichromosomal structure with a total length of 449,613 bp. A total of 51 genes were detected, including 14 core genes, 15 tRNA genes, 19 variable genes and 3 rRNA genes. Three types of repetitive sequences were detected, including 121 simple repetitive sequences, 12 tandem repetitive sequences and 112 scattered repetitive sequences. A total of 9,810 codons encoding 33 PCGs were detected, and the probability of codon preference and avoidance was 50% and 47%, respectively. A total of 454 effective RNA editing sites were detected, distributed on 30 PCGs with all base change types C-U. 84 inter-genome transfer fragments were identified, and four complete transfer DNA fragments were rps12 , trnS-UGA , trnM-CAU and trnN-GUU , respectively. The rps3 gene showed positive selection (Ka/Ks > 1) in 36 (90%) of 40 species, indicating that it may be a functional gene adapted to rapid evolution. The Pi values of 33 genes ranged from 0 to 0.16277. Phylogenetic analysis divided 43 species into 6 categories. Combined with the results of collinearity, it was found that Festuca pratensis had the closest genetic relationship with Lolium perenne . In this study, the first high-quality mitochondrial genome of Festuca pratensis was assembled, which provided key high-quality reference data for subsequent organelle genome evolution, stress-resistant functional gene mining and germplasm resource identification of related species.

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