Armillaria species hold significant ecological and economic importance and they play a vital role in the growth of traditional Chinese medicine Gastrodia elata (G. elata). In this study, we assembled and compared the mitochondrial genomes (mitogenomes) of six Armillaria mellea (Vahl) P. Kumm. (A. mellea) strains isolated from the main G. elata-producing region of Hanzhong, China. The internal transcribed spacer (ITS) sequencing confirmed that all six strains form a monophyletic clade. Their mitogenomes (120,775 to 120,839 bp) exhibit a highly conserved architecture, each containing 16 protein-coding genes (PCGs), 23 open reading frames (ORFs), 27 tRNAs, and two rRNAs. Codon usage and amino acid frequency were strikingly similar among the six strains, with a strong AT bias. In contrast, comparisons with other Armillaria species revealed marked differences in gene order, repeat structures, and selection pressures. Phylogenetic analyses based on PCGs further resolved the close relationship among the six strains while highlighting distinct molecular variation across species. On the whole, these findings demonstrate that A. mellea strains co-evolving with G. elata maintain a highly uniform mitochondrial genome architecture, suggesting strong purifying selection or recent divergence within this symbiotic population. The pronounced differences from other Armillaria species at the levels of gene arrangement and selection pressure imply that mitochondrial gene rearrangement may have accompanied species diversification in the genus. By providing the first complete mitogenomes of A. mellea from a major G. elata cultivation area, this study not only expands the genomic resources for Armillaria but also establishes a foundation for understanding how mitochondrial variation might influence fungal growth, adaptation, and symbiotic efficiency with G. elata.
Jiang et al. (Fri,) studied this question.