Genetic disruptions of Hsp90-encoding genes impacted short-term evolutionary trajectories of antifungal resistance in Saccharomyces cerevisiae

Laboratory evolution has been a powerful approach to address questions about evolvability. It has been debated whether the molecular chaperone, heat shock protein 90 (Hsp90), buffers or potentiates the effects of variation, and, consequently, constrains or accelerates evolution. In this study, we experimentally evolved yeast strains carrying mutant alleles of Hsp90-encoding genes under mild clotrimazole selection. We found that knockout of HSC82, which encodes a constitutively expressed Hsp90 chaperone, led to slower evolution of clotrimazole resistance in the short term. However, all strains generally evolved resistance within seven transfers, regardless of Hsp90 status. Through whole-genome sequencing, we identified genetic changes associated with clotrimazole resistance, including prevalent mitochondrial genome loss, as well as chromosomal duplications and point mutations. HSC82 knockout populations specifically showed convergent chromosomal duplications of chrVIII and chrXV. Taken together, our results demonstrate that disruption of Hsp90 in yeast may not alter the overall outcome of evolution but may shape its evolutionary trajectories at both the phenotypic and genotypic levels.