Structural Diversity and Phylogenomic Insights from the Mitochondrial Genomes of Two Populus Species from the Qinghai-Tibet Plateau

Congde Huang^1*Jin-Liang Huang¹YuJie Shi²Fei-Fei Tian¹Jia-Xuan Mi³Fan Zhang⁴Shixing Zhou¹Xue-Qin Wan¹

• ¹College of Forestry, Sichuan Agricultural University, Chengdu, China
• ²Taizhou University, Taizhou, China
• ³Southwest Forestry University, Kunming, China
• ⁴Sichuan Agricultural University,College of Landscape Architecture, chengdu, China

Populus kangdingensis and Populus ciliata are important tree species distributed across the Qinghai–Tibet Plateau, yet the structure and evolutionary characteristics of their mitochondrial genomes remain unclear. To elucidate these features and their phylogenetic relationships, we assembled and annotated the mitogenomes of both species using PacBio HiFi sequencing data. The results revealed that the mitogenome of P. kangdingensis consists of three independent circular molecules with a total length of 785,824 bp, while P. ciliata possesses a branched conformation comprising two circular and one linear molecule, totaling 798,807 bp. Both genomes contain 57 functional genes, including 34 protein-coding genes, which are highly conserved. Comparative analyses indicated differences in repeat sequences, RNA editing patterns, and chloroplast-derived sequences, suggesting species-specific evolution at the organellar genome level. Ka/Ks analysis identified genes such as atp4, ccmB, and mttB as potentially under positive selection, reflecting adaptation to high-altitude environments. Phylogenetic trees constructed using 30 mitochondrial and 58 chloroplast PCGs confirmed the monophyly of Populus and Salix, with the two resolving as sister. However, topological inconsistencies within genera point to the influence of lineage sorting , hybridization and differences in rates of mutation. This study provides valuable insights into mitogenome evolution and phylogenetics in Populus.