Exserohilum turcicum and Exserohilum rostratum Genome sequencing and assembly. Exserohilum turcicum, Exserohilum rostratum

Exserohilum turcicum and E. rostratum, two closely related fungal species, are both economically important pathogens but have quite different target hosts (specific to plants and cross-kingdom infection, respectively). In the present study, complete mitochondrial genomes of the two Exserohilum species were sequenced, assembled, annotated and compared. Both the mitogenomes consist of circular DNA molecules, comprising a set of core protein-coding genes (PCGs), rRNAs, tRNAs and unidentified ORFs, but with vastly different sizes, 264,948 bp and 64,620 bp, respectively. Comparative mitogenomic analysis showed that these two fungi had rather consistent mitochondrial gene arrangement, though three tRNAs (trnN-3, trnC-2 and trnV-2) were absent in E. rostratum. However, by contrast with the 17 introns containing 17 intronic ORFs in E. rostratum mitogenome, E. turcicum involves far more introns (70) and intronic ORFs (126), which was considered as the main contributing factor of their mitogenome expansion/contraction. Within the generally intron-rich gene cox1, a total of 18 and 10 intron position classes (Pcls) were identified separately in the two mitogenomes. Moreover, 16.16% and 10.85% ratios of intra-genomic repetitive regions were detected in E. turcicum and E. rostratum, respectively. Based on the combined mitochondrial gene dataset, we obtained a well-supported topology of phylogenetic tree for 98 ascomycetes, implying that mitogenome is possibly an effective molecular marker for phylogeny reconstruction. This study served as the first report on mitogenomes in the genus Exserohilum, which could have implications in understanding the genetics and evolution of Exserohilum species.