Poster Annual Conference of the Genetics Society of Australasia with the NZ Society for Biochemistry & Molecular Biology

Independent loss of introns during evolution across multiple fungal clades (680)

Chun Shen Lim 1 , Christopher Brown 1
  1. Department of Biochemistry, University of Otago, Dunedin, New Zealand

Most eukaryotic genes are interrupted by introns. Intron removal requires an expensive, complex splicing mechanism. Since discovery, introns have been shown to have multiple roles in transcription and translation. Here, we used over 600 fungal genomes to investigate the evolution of introns in fungi. Current evolutionary models propose that the genes in the last eukaryotic common ancestor have a density of introns of ~4 intron/kb. Intron density varies widely in fungal kingdom, ranging from 0.1 intron/kb in the Saccharomyces cerevisiae (less than 5% of genes have introns) to over 4 intron/kb in other ascomycetes. Some distantly related basidiomycetes also have low intron density, e.g., below 0.5 intron/kb in Ustilago maydis (only 28% genes have introns). This raises the question — why do fungi retain introns when most can be dispensed with? To address this question, over 1000 fungal orthologous genes were identified and patterns of intron distribution examined. We found that the introns that are independently retained during evolution are enriched in some classes of genes, e.g., ribosomal protein genes. Whereas introns are depleted in others, e.g., base-excision repair genes. Analysis of publicly available ribosome profiling datasets for intron-poor S. cerevisiae, Candida albicans, Schizosaccharomyces pombe, and Neurospora crassa suggest that the remaining introns are associated with genes with higher translation efficiency. These findings suggest that one reason for the retention of introns during evolution relates to a role in translation.