Alternative splicing (AS) is a cellular process that increases a cell's coding capacity from a limited set of genes. Although AS is common in higher plants and animals, its prevalence in other eukaryotes is mostly unknown. In fungi the involvement of AS in gene expression and its effect on multi-cellularity and virulence is of great medical and economic interest. We present a genome-wide comparative study of AS in 23 informative fungi of different taxa, based on alignments of public transcript sequences. Random sampling of expressed sequence tags allows for robust and comparable estimations of AS rates. We find that a greater fraction of fungal genes than previously expected is associated with AS. We estimate that on average, 6.4% of the annotated genes are affected by AS, with Cryptococcus neoformans showing an extraordinary rate of 18%. The investigated Basidiomycota show higher average AS rates (8.6%) than the Ascomycota (6.0%), although not significant. We find that multi-cellular complexity and younger evolutionary age associate with higher AS rates. Furthermore, AS affects genes involved in pathogenic lifestyle, particularly in functions of stress response and dimorphic switching. Together, our analysis strongly supports the view that AS is a rather common phenomenon in fungi and associates with higher multi-cellular complexity.
Keywords: alternative splicing; fungal genomes; multi-cellular complexity; retained intron; transcriptome analysis.