Transcriptome Kinetics of Saccharomyces cerevisiae in Response to Viral Killer Toxin K1

Abstract

The K1 A/B toxin secreted by virus-infected Saccharomyces cerevisiae strains kills sensitive cells via disturbance of cytoplasmic membrane functions. Despite decades of research, the mechanisms underlying K1 toxicity and immunity have not been elucidated yet. In a novel approach, this study aimed to characterize transcriptome changes in K1-treated sensitive yeast cells in a time-dependent manner. Global transcriptional profiling revealed substantial cellular adaptations in target cells resulting in 1,189 differentially expressed genes in total. Killer toxin K1 induced oxidative, cell wall and hyperosmotic stress responses as well as rapid down-regulation of transcription and translation. Essential pathways regulating energy metabolism were also significantly affected by the toxin. Remarkably, a futile cycle of the osmolytes trehalose and glycogen was identified probably representing a critical feature of K1 intoxication. In silico analysis suggested several transcription factors involved in toxin-triggered signal transduction. The identified transcriptome changes provide valuable hints to illuminate the still unknown molecular events leading to K1 toxicity and immunity implicating an evolutionarily conserved response at least initially counteracting ionophoric toxin action.

Yeast Viral Killer Toxin K1 Induces Specific Host Cell Adaptions via Intrinsic Selection Pressure

“…Furthermore, we were interested in comparing the transcriptome adaptations of both strains after the addition of external toxin, as well as the basal differences in expression levels. In contrast to a previously conducted study analyzing transcriptome adaptations of a sensitive strain, only a few genes were found to be significantly deregulated in both K1 killer strains (16). Although the expression of some genes was altered in both strains, the K1-sensitive strain KIM01s showed a generally stronger response when incubated with additional K1.…”

“…This leaky immunity correlates with findings displaying the same phenotype when K1 toxin is expressed via a centromeric plasmid (19). However, we previously were able to demonstrate that the formation of toxin-induced pores takes place considerably before a significant decrease in cell viability of sensitive cells can be observed (16). Based on this observation, a corresponding analysis correlating the percentage of PI-positive and living cells using the killer strains could help to determine whether K1 toxin is able to merely insert into the plasma membrane of its producing host cell or whether the killer yeast is effectively killed during the process.…”

“…Toxin production and concentration were conducted as described before (16). Activity of K1 toxin was analyzed via agar diffusion assay using SC-glucose MBA supplemented with appropriate amino acids and nucleotide supplementation (0.5% ammonium sulfate, 1.92% citrate, 2% glucose, 0.17% yeast nitrogen base, 1.5% agar, and methylene blue [pH 4.7]) as described previously (16). Likewise, the mediation of intrinsic immunity of KIM01 and KIM01s against externally applied K1 toxin was analyzed.…”

“…The current model of K1 action considers both, the possibility of direct insertion of the toxin into plasma membrane structures, as well as interaction with as-yet-unknown primary effectors (11,15). In a recent study, we were able to characterize the transcriptome kinetics of a sensitive strain in response to K1, revealing insights into both the K1 lethal effects and the possible defense mechanisms of the target cell (16).…”

Analysis of Yeast Killer Toxin K1 Precursor Processing via Site-Directed Mutagenesis: Implications for Toxicity and Immunity

“…Cells were grown at 30°C in standard growth medium (1% yeast extract, 2% peptone, 2% glucose). Toxin production and concentration were determined as described before (33).…”