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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., (Copyright © 2018. Published by Elsevier B.V.)

Lyophyllum decastes and Lyophyllum shimeji are the two primary species within the L. decastes complex, and they differ considerably in their nutritional lifestyles and preferred growth environments. However, differences in their mitogenomes have not yet been investigated. In this study, the mitogenomes of the two species were sequenced by next-generation sequencing technology, successfully assembled, and compared. The two mitogenomes of L. decastes and L. shimeji comprised circular DNA molecules of sizes 50,643 bp and 73,678 bp, respectively. The lengths and base compositions of their core protein coding genes (PCGs) and tRNA genes varied considerably between the two mitogenomes. Further, gene collinearity analysis indicated a large-scale gene rearrangement between the two mitogenomes. Of the 15 core PCGs, the genetic distance of the atp9 gene was the smallest between the two species, indicating that this gene was highly conserved in the two Lyophyllum species. Phylogenetic analysis based on a combined mitochondrial gene dataset resulted in a well-supported topology, wherein the two Lyophyllum species were most closely related to Tricholoma matsutake. This study represents the first report of mitogenomes for the Lyophyllum genus. As such, the results will provide a basis for understanding the differentiation and evolution of mitogenomes in the Lyophyllum genus., (Copyright © 2018. Published by Elsevier B.V.)

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., (Copyright © 2018. Published by Elsevier B.V.)