Interactions Between Chloroplast and Mitochondrial Genomes in 11 Salix Species

Yeseul KimSumin JeongShukherdorj BaasanmunkhYoungmoon KimHyeok Jae ChoiInkyu Park^*

• Changwon National University, Changwon, Republic of Korea

The genus Salix, widely distributed across the Northern Hemisphere, is characterized by its dioecious nature and frequent natural hybridization. It has significant ecological and economic value in landscaping, ornamentation purposes, biomass production, and traditional medicine. Understanding its evolutionary dynamics is crucial for effective conservation and sustainable utilization. While hybridization and intracellular gene transfer offer valuable insights into its genetic architecture and evolutionary trajectories, studies examining both chloroplast and mitochondrial genomes remain limited. In this study, we sequenced and assembled the chloroplast and mitochondrial genomes of male and female individuals from three closely related Salix species, namely S. pierotii, S. babylonica, and S. pseudolasiogyne. We also included data from eight additional Salix species for comparison. The chloroplast genomes ranged from 155,688 to 155,695 bp, and the mitochondrial genomes from 705,072 to 705,179 bp, with repetitive sequences occupying a similar proportion of both organelle genomes. Phylogenetic analysis of the 11 Salix species revealed two main clades corresponding to the Salix and Vetrix subgenera, with an estimated initial divergence time at approximately 25–26 MYA. Discrepancies between chloroplast-and mitochondrial-based phylogenies likely reflect differences in genome evolution, including structural dynamics and sequence divergence. Positive selection analysis further indicated that certain mitochondrial genes experienced stronger selective pressures than chloroplast genes, highlighting the distinct adaptive evolutionary trajectories. The presence of homologous fragments between the chloroplast and mitochondrial genomes supports the occurrence of intracellular gene transfer, a key factor in the genomic evolution and species diversification of Salix. Notably, the mitochondrial tree revealed an alternating pattern between S. pierotii and S. pseudolasiogyne individuals, which may reflect potential gene flow, thereby providing tentative evidence of complex genomic interactions between these species. This study highlights the importance of mitochondrial genome analysis in Salix, providing insights into organelle genome evolution and the impact of gene flow on genetic diversity and evolutionary dynamics.