Putative Group I Introns in the Nuclear Internal Transcribed Spacer of the Basidiomycete Fungus Gautieria Vittad

Group I introns are self-splicing ribozymes that insert into protein and RNA coding genes. In ribosomal RNA genes, group I introns can intervene the small subunit (SSU) and large subunit (LSU) of various prokaryotic and lower eukaryotic organisms including protists and fungi. However, it is unusual to encounter them in the nuclear internal transcribed spacer (ITS) region. In this study, exceptionally long ITS regions of the fungal species from the genus Gautieria were analyzed. The unusually long ITS region of a newly isolated Gautireia specimen (ANK Akata and Sahin 001) and ITS sequences of the G. monticola isolates present in GenBank were bioinformatically analyzed. In addition to the presence of tandem repeats, the increased size of the ITS sequences analyzed herein was found to be due to the presence of group I introns in the ITS1 regions of both newly isolated specimen and different isolates of G. monticola. The secondary structures of the identified introns could be formed in accordance with the group I intron models, and they clustered with group I introns in conserved core domain-based phylogeny. The molecular phylogenetic analysis performed based on the ITS sequences of the genus Gautieria revealed the occurrence of at least two independent intron invasion event in the evolutionary process of this genus. This is the first study reporting on the presence of group I introns in the ITS region of a higher fungus.