Sung Jin MoonP, Young-Ho Ha, Jei-Wan Lee, Ji-Young Ahn*

Department of Forest Bio-Resources, National Institute of Forest Science, Onjeongro 39, 16631 Suwon, Republic of Korea

Koelreuteria paniculata (Sapindaceae) is an economically and culturally important species valued for its ornamental traits, durable wood, and medicinal use. Plant mitochondrial (MT) genomes exhibit complex structures and size variations, providing valuable insights into species identification and evolution. Herein, we report the first complete MT genome sequence of K. paniculata. The complete circular genome (610,364 bp; GC 41.4%) contains 58 unique genes: 32 protein-coding, 4 ribosomal RNA, and 22 transfer RNA genes. A 2,047-bp chloroplast-derived fragment containing rrn16 and trnV-GAC was verified to be transferred into the MT genome. Additionally, we identified 197 simple sequence repeats and 352 dispersed repeats, with the longest repeats spanning 2,084 bp. Codon usage favored A/U-ending codons, a conserved feature in terrestrial plants. Moreover, 468 C-to-U RNA-editing sites were predicted across the 32 protein-coding genes (PCGs), with nad4 being the most affected. For 25 shared PCGs among Sapindaceae species, the mean Ka/Ks ratio (0.64) indicated purifying selection; meanwhile, atp8, matR, and nad2 showed positive selection, implying adaptive evolution. Phylogenetic analysis of 28 conserved PCGs placed K. paniculata within Sapindaceae. Comparative analysis revealed dynamic MT rearrangements within the family. Conclusively, this study contributes to our understanding of the genome architecture and evolutionary dynamics of K. paniculata.

Funding: This work was supported by the National Institute of Forest Science (grant number FG0603-2025-01-2024 to author Ji-Young Ahn).