title: Comparison of mitochondrial genomes provides insights into intron dynamics and evolution in the caterpillar fungus Cordyceps militaris.
abstract: Intra-specific comparison of mitochondrial genomes can help elucidate the evolution of a species, however it has not been performed for hypocrealean fungi that form diverse symbiotic associations with other organisms. In this study, comparative analyses of three completely sequenced mitochondrial genomes of a hypocrealean fungus, Cordyceps militaris, the type species of Cordyceps genus, revealed that the introns were the main contributors to mitochondrial genome size variations among strains. Mitochondrial genes in C. militaris have been invaded by group I introns in at least eight positions. PCR assays of various C. militaris isolates showed abundant variations of intron presence/absence among strains at seven of the eight intronic loci. Although the ancestral intron pattern was inferred to contain all eight introns, loss and/or gain events occurred for seven of the eight introns. These introns invaded the C. militaris mitochondrial genome probably by horizontal transfer from other fungi, and intron insertions into intronless genes in C. militaris were accompanied by co-conversions of upstream exon sequences especially for those introns targeting protein-coding genes. We also detected phylogenetic congruence between the intron and exon trees at each individual locus, consistent with the ancestral mitochondria of C. militaris as having all eight introns. This study helps to explain the evolution of C. militaris mitochondrial genomes and will facilitate population genetic studies of this medicinally important fungus.
authors.affiliation: School of Life Sciences, Shanxi University, Taiyuan 030006, China. Electronic address: zhangyj2008@sxu.edu.cn.
authors.forename: Yongjie
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Life Sciences, Shanxi University, Taiyuan 030006, China.
authors.forename: Shu
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Plant Pathology, China Agricultural University, Beijing 100193, China.
authors.forename: Guozhen
authors.initials: G
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Xingzhong
authors.initials: X
authors.lastname: Liu
authors.affiliation: Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Chengshu
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada. Electronic address: jpxu@mcmaster.ca.
authors.forename: Jianping
authors.initials: J
authors.lastname: Xu
mesh_terms: D000818:Animals; D032661:Cordyceps / Q000235:genetics* / Q000472:pathogenicity / Q000648:ultrastructure; D019143:Evolution, Molecular; D005091:Exons; D022761:Gene Transfer, Horizontal; D054629:Genome, Mitochondrial; D007438:Introns; D007814:Larva / Q000382:microbiology; D024101:Mitochondrial Proteins / Q000235:genetics; D010802:Phylogeny
chemical_list: D024101:Mitochondrial Proteins
keywords: Co-conversion; Cordyceps militaris; Horizontal gene transfer; Intron dynamics; Mitochondrial genome