Evolution of Fungal U3 snoRNAs: Structural Variation and Introns

The fungal snoRNAome

Small nucleolar RNAs (snoRNAs) are essential players in the rRNA biogenesis due to their involvement in the nucleolytic processing of the precursor and the subsequent guidance of nucleoside modifications. Within the kingdom Fungi, merely a few species-specific surveys have explored their snoRNA repertoire. However, the wide range of the snoRNA landscape spanning all major fungal lineages has not been mapped so far, mainly because of missing tools for automatized snoRNA detection and functional analysis. For the first time, we report here a comprehensive inventory of fungal snoRNAs together with a functional analysis and an in-depth investigation of their evolutionary history including innovations, deletions, and target switches. This large-scale analysis, incorporating more than 120 snoRNA families with more than 7700 individual snoRNA sequences, catalogs and clarifies the landscape of fungal snoRNA families, assigns functions to previously orphan snoRNAs, and increases the number of sequences by 450%. We also show that the snoRNAome is subject to ongoing rearrangements and adaptations, e.g., through lineage-specific targets and redundant guiding functions.