Characterization and comparative mitogenomic analysis of six newly sequenced mitochondrial genomes from ectomycorrhizal fungi (Russula) and phylogenetic analysis of the Agaricomycetes

In this study, the mitochondrial genomes of six Russula species were sequenced using next generation sequencing. The six mitogenomes were all composed of circular DNA molecules, with lengths ranging from 40,961 bp to 69,423 bp. The length and number of protein coding genes (PCGs), GC content, AT skew, and GC skew varied among the six mitogenomes. The increased number and total size of introns likely contributed to the size expansion of mitogenomes in some Russula species. Gene synteny analysis revealed some gene rearrangements among the six mitochondrial genomes. The nad4L gene had the lowest K2P genetic distance of the 15 core PCGs among the six Russula species, indicating that this gene was highly conserved. The Ka/Ks values for all 15 core PCGs were <1, suggesting that they were all subject to purifying selection. Phylogenetic analyses based on two gene datasets (15 core PCGs, and 15 core PCGs + rnl + rns) recovered identical and well-supported trees. In addition, cox1 was identified as a potential single-gene molecular marker for the phylogenetic analysis of relationships among Agaricomycetes species. This study provides the first report of mitogenomes from the Russulaceae family and facilitates the investigation of population genetics and evolution of other ectomycorrhizal fungi.