Related Experiment Video
Updated: Jun 21, 2026

Sexual Crosses with the Mucoromycete Phycomyces blakesleeanus
Published on: June 6, 2025
Evolutionary diversification indicated by compensatory base changes in ITS2 secondary structures in a complex fungal
Paavo Ahvenniemi1, Matthias Wolf, Mari J Lehtonen
1Department of Applied Biology, University of Helsinki, Finland.
Abstract:
The rRNA cistron (18S-ITS1-5.8S-ITS2-28S) is used widely for phylogenetic analyses. Recent studies show that compensatory base changes (CBC) in the secondary structure of ITS2 correlate with genetic incompatibility between organisms. Rhizoctonia solani consists of genetically incompatible strain groups (anastomosis groups, AG) distinguished by lack of anastomosis between hyphae of strains. Phylogenetic analysis of internal transcribed spacer (ITS) sequences shows a strong correlation with AG determination. In this study, ITS sequences were reannotated according to the flanking 5.8S and 28S regions which interact during ribogenesis. One or two CBCs were detected between the ITS2 secondary structure of AG-3 potato strains as compared to AG-3 tobacco strains, and between these two strains and all other AGs. When a binucleate Rhizoctonia species related to Ceratobasidiaceae was compared to the AGs of R. solani, which were multinucleate (3-21 nuclei per cell), 1-3 CBCs were detected. The CBCs in potato strains of AG-3 distinguish them from AG-3 tobacco strains and other AGs yielding further evidence that the potato strains of AG-3 originally described as R. solani are a species distinct from other AGs. The ITS1-5.8S-ITS2 sequences were analyzed by direct sequencing of PCR products from 497 strains of AG-3 isolated from potato. The same 10 and 4 positions in ITS1 and ITS2, respectively, contained variability in 425 strains (86%). Nine different unambiguous ITS sequences (haplotypes) could be detected in a single strain by sequencing cloned PCR products indicating that concerted evolution had not homogenized the rRNA cistrons in many AG-3 strains. Importantly, the sequence variability did not affect the secondary structure of ITS2 and CBCs in AG-3.
More Related Videos
08:11Adaptation at the Extremes of Life: Experimental Evolution with the Extremophile Archaeon Sulfolobus acidocaldarius
Published on: June 14, 2024
06:58Isolation, Behavioral Identification, and Pathogenicity Assessment of Entomopathogenic Fungi from a Forest Wood Borer
Published on: September 29, 2023
Related Concept Videos
Diversity of Protists III
Fungal Group Zygomycota
Protein Complexes with Interchangeable Parts
The SCF ubiquitin ligase is a protein complex of five individual proteins. This complex attaches ubiquitin to other target proteins to mark them for degradation. In order to...
Diversity of Protists II
Evolution of New Traits in Microbes
Fungal Phylum Basidiomycota