The memory of hyperosmotic stress response in yeast is modulated by gene-positioning

Cellular memory is a critical ability displayed by microorganisms in order to adapt to potentially detrimental environmental fluctuations. In the unicellular eukaryote S. cerevisiae cellular memory can take the form of a faster or a decreased response following repeated stresses in cell population. Using microfluidics and fluorescence time-lapse microscopy, we studied how yeasts respond to short-pulsed hyperosmotic stresses at the single-cell level by analyzing the dynamical behavior of the stress responsive STL1 promoter fused to a fluorescent reporter. We established that pSTL1 shows variability in its successive activations following two repeated short stresses. Despite this variability, most cells displayed a memory of past stresses through a decreased activity of pSTL1 upon repeated stress. Notably, we showed that genomic location is important for the memory effect since promoter displacement to a pericentromeric chromatin domain leads to a decreased transcriptional strength of pSTL1 and to the loss of memory. This study provides a quantitative description of a cellular memory that includes single-cell variability and points towards the contribution of the chromatin structure in stress memory.