Analysis of the mitochondrial genome of the Camellia sinensis cv. ‘Zhuyeqi’: multichromosomal structure, RNA editing sites, and evolutionary characterization

The mitochondrial genome of 'Zhuyeqi' consists of one circular chromosome and six linear chromosomes, with a total length of 911,255 bp and a GC content of 46%. Genome annotation identified 77 functional genes, including 38 protein-coding genes (PCGs). The study revealed heterogeneously distributed introns within genes such as trnM-CAT (5 copies) and <i>nad1/2/5/7</i>. RNA editing analysis identified 556 C-to-U editing sites, notably enriched in <i>ccmFn</i> (38 sites) and <i>ccmB</i> (34 sites). Codon usage bias analysis indicated that leucine (Leu, 10%) and arginine (Arg, 7%) were the most frequently used amino acids. Repeat sequence analysis showed that dispersed repeats (780, 72%) dominated, with satellite DNA exhibiting significant distribution biases on <i>chr1</i> (11) and <i>chr3</i> (5). Ka/Ks analysis revealed that 37 PCGs were under varying selective pressures (0.09-2.70), with <i>rps4</i> (Pi=0.09) and <i>atp8</i> (Pi=0.09) showing exceptionally high variability, while <i>rps19</i> (Pi=0) was completely conserved. Comparative genomics uncovered 66 homologous segments (25,656 bp) between the mitochondrial and chloroplast genomes, containing 27 intact genes such as <i>trnA-UGC</i>, confirming horizontal gene transfer events. Collinearity analysis demonstrated a high degree of conservation in genomic structures between 'Zhuyeqi' and closely related <i>Camellia</i> species. This study lays an important theoretical foundation for further elucidating the structural characteristics and evolutionary mechanisms of the tea plant mitochondrial genome.