A study on the intron landscape of the cytochrome b gene, and mitochondrial-encoded N-acetyltransferase and ribosomal protein S3 genes of fungi in the subphylum Pezizomycotina
Mitochondrial genomes (mtDNAs) of fungi are highly variable in size. The variability can be partially attributed to the presence/absence of introns/intron-encoded open reading frames (ORFs) and genes. In order to study their effects on fungal mtDNAs, the potential intron insertion sites within the cytochrome b (cytb) gene and the distribution of mitochondrial-encoded N-acetyltransferase (NAT) and ribosomal protein S3 (rps3) genes were examined. The study on intron distribution in the cytb gene resulted in generation of an intron landscape. Many different intron/ORF arrangements were noted, potentially representing introns/ORFs at different stages of their life cycle. Based on the findings, a model of the life cycle of mobile composite elements was proposed. Both NAT and rps3 genes can be freestanding or intron-encoded. Based on phylogenetic analysis, NAT genes may have been imported in the mtDNA whereas the rps3 gene may have been imported into the nucleus in some fungi. The findings of the work suggest that the mtDNA is dynamic and contracts and expands due to factors including mobile introns/intron-encoded ORFs and genes.