Developmentally regulated MAPK pathways modulate heterochromatin in Saccharomyces cerevisiae

Variegated expression of genes contributes to phenotypic variation within populations of genetically identical cells. Such variation plays a role in development and host pathogen interaction and can be important in adaptation to harsh environments. The expression state of genes placed near telomeres shows a variegated pattern of inheritance due to heterochromatin formation, a phenomenon that is called telomere position effect (TPE). We show that in budding yeast, TPE is controlled by the a1/alpha2 developmental repressor, which dictates developmental decisions in response to environmental changes. Two a1/alpha2 repressed genes, STE5, a MAPK scaffold and HOG1, a stress-activated MAPK, are the targets of this heterochromatin regulation pathway. We provide new evidence that link MAPK signaling and heterochromatin formation in yeast. Our results show that the same components that regulate gene expression states in euchromatic regions regulate heterochromatic expression states and that stress can play a part in turning on or off genes placed in heterochromatic regions.