The Mitochondrial Genome of the Glomeromycete Rhizophagus sp. DAOM 213198 Reveals an Unusual Organization Consisting of Two Circular Chromosomes

nadimi, maryam ; stefani, franck, o.p ; hijri, mohamed;

Mitochondrial (mt) genomes are intensively studied in Ascomycota and Basidiomycota, but they are poorly documented in basal fungal lineages. In this study, we sequenced the completemt DNA of Rhizophagus sp.DAOM213198, a close relative to Rhizophagus irregularis, a widespread, ecologically and economical relevant species belonging to Glomeromycota. Unlike all other known taxonomically close relatives harboring a full-length circular chromosome, mtDNA of Rhizophagus sp. reveals an unusual organization with two circular chromosomes of 61,964 and 29,078 bp. The large chromosome contained nine protein-codinggenes (atp9,nad5, cob,nad4,nad1,nad4L,cox1,cox2,and atp8), small subunitr RNA gene (rns), and harbored 20tRNA- coding genes and 10orfs,while the small chromosome contained five protein-coding genes (atp6, nad2, nad3, nad6, andcox3), large subunit rRNA gene (rnl) in addition to 5tRNA-coding genes, and 8plasmid-related DNA poly merases (dpo). Although structural variation of plant mtgenomesis well documented, this study is the first report of the presence of two circular mt genomes in arbuscular mycorrhizal fungi. Interestingly, the presence of dpo at the breakage point in intergenes cox1-cox2 and rnl-atp6 for large and small mtDNAs, respectively, could be responsible for the conversion of Rhizophagus sp. mtDNA into two chromosomes. Using quantitative real-time poly merase chain reaction, we found that both mtDNAs have an equalabundance.This study reports a novel mt DNA organization in Glomeromycota and highlights the importance of studying early divergent fungal lineages to describe novel evolutionary pathways in the fungal kingdom