The first complete mitochondrial genome from the family Hygrophoraceae (Hygrophorus russula) by next-generation sequencing and phylogenetic implications.

Hygrophorus russula (Schaeff.) Kauffman is an edible ectomycorrhizal fungus that is widely distributed in the world. In this study, the mitogenome of H. russula was sequenced and assembled. The mitogenome of H. russula is composed of circular DNA molecules, with a total size of 55,769 bp. Further analysis indicated that the frequent use of A and T in codons contributes to the high AT content (80.87%) in the H. russula mitogenome. Comparative analysis indicated that the length and base composition of the core protein-encoding genes, and the number of tRNA genes in the H. russula mitogenome varied from that of other Agaricales mitogenomes. Gene arrangement analysis revealed a novel gene order in the H. russula mitogenome. In addition, the expansion of the mitogenome in Agaricales was found to be closely related to the increase in the number of introns. Phylogenetic analysis of the combined mitochondrial gene set showed strong support for tree topologies, and H. russula was determined to be relatively distant from other Agaricales species. This study is the first report on the mitogenome of a member of genus Hygrophorus as well as family Hygrophoraceae, which improves our understanding of mitochondrial differentiation and evolution in the important ectomycorrhizal fungi Hygrophorus species.