Characterization of the Complete Mitochondrial Genome of Castanopsis tibetana Hance: A Precious Timber Species

Background/Objectives: Castanopsis tibetana Hance (C. tibetana) is a valuable timber species in southern China. Its chloroplast and nuclear genomes have been characterized, but its mitochondrial genome (mitogenome) remains unknown. This study assembles and characterizes the first complete mitogenome of C. tibetana, elucidating its structural and evolutionary features. Methods: A hybrid approach combining Oxford Nanopore long reads and Illumina short reads was used. The mitogenome was assembled via iterative seed-based mapping and annotated via GeSeq and tRNAscan-SE. Repeats were identified via MISA, TRF, and REPuter. The RNA editing sites were predicted with the PREP suite. Phylogenetic analysis was performed on 14 conserved protein-coding genes from 13 species via maximum likelihood and Bayesian inference. Results: The mitogenome is a 554,078 bp circular molecule (GC 45.27%) encoding 51 genes (32 PCGs, 16 tRNAs, 3 rRNAs). It contains 202 simple sequence repeats (37.1% tetrameric). We predicted 53 C-to-U RNA editing sites, most frequently in nad7 and nad5. Codon usage showed bias, with 28 codons having RSCU > 1. Twenty fragments (6001 bp, 1.08% of the mitogenome) were transferred from the chloroplast. Phylogenomic analysis placed C. tibetana within Fagaceae, close to other Castanopsis species. Conclusions: This study provides the first comprehensive characterization of the C. tibetana mitogenome, revealing its structural architecture, repetitive landscape, RNA editing profile, and phylogenetic placement. These findings offer valuable genomic resources for understanding mitogenome evolution in Fagaceae and support future research on the conservation genetics and molecular breeding of this important tree species.