Comparative mitogenomic analysis reveals variations and evolution of ectomycorrhizal fungal Strobilomyces

The genus Strobilomyces, representing a diverse and widespread group of ectomycorrhizal mushroom-forming fungi, plays a crucial ecological and economical role. However, until now, a comprehensive description of its mitochondrial genome (mitogenome) has been lacking. In our current study, we have successfully assembled and analysed the mitogenomes of five Strobilomyces species. These mitogenomes span a range from 35,618 base pairs (bp) to 42,088 bp, exhibiting a higher nucleotide abundance of AT compared to GC. All five mitogenomes harbour 14 conserved protein-coding genes (PCGs), two ribosomal RNAs (rRNAs) and 24 transfer RNAs (tRNAs). Notably, the overall ratio of Ka/Ks for all PCGs was found to be less than 1.0, indicating that these genes have undergone purifying selection during evolution. Intriguingly, the mitogenomic comparison revealed two instances of gene re-arrangement, which were directly linked to the geographical distribution of the Strobilomyces species. The concatenated mitochondrial PCGs (mtPCGs) and nuclear ribosomal DNA (nrDNA) phylogenies displayed a robust congruent topology at the family level. Specifically, the Strobilomyces species clustered together and formed sister relationship with other Boletaceae species in the mtPCGs tree. In contrast, the Strobilomyces species grouped at the base of the nrDNA tree when concerning Boletaceae. This study represents the first report on the mitogenomes of the Strobilomyces genus, providing valuable insights into fungal evolution within Boletales.