# Molecular evolution of the members of the Snq2/Pdr18 subfamily of Pdr transporters in the Hemiascomycete yeasts

## TL;DR

This study explores the evolutionary history of drug resistance transporters in yeasts, revealing their origins and patterns of selection.

## Contribution

The study identifies the horizontal transfer origin of Snq2/Pdr18 genes and traces their evolutionary divergence in hemiascomycete yeasts.

## Key findings

- Early-divergent yeast species lack Snq2/Pdr18 homologs, suggesting a horizontal gene transfer origin.
- The PDR18 ortholog has been under strong diversifying selection after gene duplication.
- Strong positive selection was observed in one paralog following a whole genome duplication event.

## Abstract

The transporters of the ATP-Binding Cassette (ABC) Superfamily involved in the Multidrug Resistance (MDR) phenomena are also known as ABC-Pleiotropic Drug Resistance (PDR) proteins. The homologs of the Saccharomyces cerevisiae SNQ2 and PDR18 genes were identified in 171 yeast genomes, representing 68 different hemiascomycetous species. All early-divergent yeast species analyzed in this work lack Snq2/Pdr18 homologs, suggesting that the origin of these ABC-PDR genes in hemiascomycete yeasts resulted from a horizontal transfer event. The evolutionary pathway of the Snq2/Pdr18 protein subfamily in pathogenic Candida species was also reconstructed, revealing a main gene lineage leading to the Candida albicans SNQ2 gene. The results indicate that, after the gene duplication event at the origin of the SNQ2/PDR18 paralogs, the PDR18 ortholog has been under strong diversifying selection and suggest that a small portion of the sequence of the SNQ2 ancestral ortholog might have been under mild positive selection. The results also showed that strong positive selection was exerted over one of the two paralogs generated by the Whole Genome Duplication (WGD) event, corresponding to the duplicate at the origin of a “short-lived” WGD sublineage.

In this study, the transporters of the ATP-Binding Cassette (ABC) Superfamily involved in the multidrug resistance phenomena, also known as ABC- Pleiotropic Drug Resistance proteins, are analyzed from an evolutionary perspective.