Whole-genome duplications contributed to the expansion of cytochrome b5 genes in Paramecium tetraurelia

Abstract

ABSTRACT. Cytochrome b 5 (cyt b 5 ) genes encode ubiquitous electron transport hemoproteins found in animals, plants, fungi, and purple bacteria. However, little is known about their evolutionary history in genomes so far. Here, we conducted an extensive genome-wide survey of cyt b 5 genes in 20 representative model species and identified 310 of these genes. Both the absolute number and relative proportion of cyt b 5 genes in Paramecium tetraurelia were significantly higher than those in other genomes. Our data also showed that whole-genome duplications (WGDs), especially the recent WGD, contributed to the species-specific expansion of cyt b 5 genes in the Paramecium genome. Furthermore, 24 cyt b 5 genes were identified as the minimal number of ancestral cyt b 5 in the ancestral Paramecium genome, which is also the largest number of these genes encountered in an organism. These results suggest that an excess of cyt b 5 genes were selectively retained in this species even before the three WGDs took place. Although more cyt b 5 genes were retained in P. tetraurelia than in other genomes, more cyt b 5 losses were