Parallel Nonfunctionalization of CK1δ/ε Kinase Ohnologs Following a Whole-Genome Duplication Event

Area of Science:

• Evolutionary biology
• Genomics
• Yeast genetics

Background:

• Whole-genome duplication (WGD) events create ohnolog pairs, offering insights into parallel gene evolution.
• The HRR25 gene in Saccharomycetaceae yeast is a rare example of maintained ohnolog pairs post-WGD.
• In Saccharomyces cerevisiae, HRR25 is essential and encodes casein kinase 1δ/ε, involved in diverse cellular functions.

Purpose of the Study:

• To investigate the hypothesis that duplicated HRR25 ohnologs were maintained through subfunctionalization.
• To functionally assess the evolutionary trajectories of HRR25 ohnologs across Saccharomycetaceae species.

Main Methods:

• Functional complementation assays using Saccharomyces cerevisiae as a model system.
• Comparative analysis of 25 HRR25 orthologs, including 7 post-WGD ohnolog pairs.
• Assessment of protein evolution rates, protein-protein interactions (PPIs), and cellular localization.

Main Results:

• No evidence of pair-dependent complementation supporting subfunctionalization was observed.
• Most post-WGD HRR25 ohnologs failed to complement, suggesting nonfunctionalization or neofunctionalization.
• Non-complementing ohnologs exhibited accelerated protein evolution, reduced PPIs, and altered cellular localization, indicative of functional decline.

Conclusions:

• The HRR25 gene family in Saccharomycetaceae is undergoing gradual nonfunctionalization of ohnologs post-WGD.
• Contrary to subfunctionalization, one copy of HRR25 appears to be losing function and becoming nonessential in some species.