Structure and Evolution of the uqcrfs1 Gene in Western Palearctic Water Frogs (Genus Pelophylax) and Implications for Systematics of Eastern Mediterranean Species

Abstract

The Rieske protein, encoded by the nuclear uqcrfs1 gene, is an essential subunit of the cytochrome bc1 complex involved in electron transfer. Despite its vital function, studies on the structure and evolution of the uqcrfs1 gene are limited. In particular, data on the fine-scale evolution of the uqcrfs1 in the context of speciation and adaptation are lacking. Eastern Mediterranean water frogs (genus Pelophylax) are an ideal model for studying such evolutionary processes at the molecular level, as they comprise several closely related lineages with different degrees of genetic and organismal divergence. Based on comprehensive sequence data of 137 frogs from 106 populations, including Mediterranean frogs as well as frogs from Europe and Central Asia, the spatial distribution of uqcrfs1 alleles was mapped and their genealogical relationships analyzed. In addition, the structure of the gene was investigated using genomic and transcriptomic data from Pelophylax lessonae. The uqcrfs1 gene consists of two exons. The length of coding sequence and its corresponding protein sequence is 807 nucleotides and 268 amino acids, respectively. The GC content and the G/C-ending codons of the gene are about 59.9% and 75.37%. The uqcrfs1 gene has a core promoter type similar to that of widely expressed housekeeping genes, with GC-rich blocks in the regulatory 5’ region, and contains many dispersed conserved motifs for transcription initiation. Genealogical analysis of the uqcrfs1 sequences revealed 10 allelic groups in the Eastern Mediterranean region. While the position of some allelic groups and the number of subgroups in the uqcrfs1 gene tree are somewhat different, they largely support the results of previous nuclear and mitochondrial genealogical studies. This gene is therefore an effective marker for determining the origin of different water frog species and lineages, including hybrids.