Yeast Dynamically Modify Their Environment to Achieve Better Mating Efficiency

By reshaping the pheromone gradient through proteolysis, yeast find partners of the opposite “sex” for mating. Enhancing Attraction to the Opposite Sex Budding yeast exist as two sexes, MATa and MATα, and the different cell types locate their opposite-sex partners through the release of pheromones; MATα cells secrete the pheromone α-factor, which stimulates growth toward and eventual mating with MATa cells. Jin et al. used simulation and experimental validation to gain insight into the mechanisms by which the secreted protease Bar1, which is produced by MATa cells and degrades α-factor, promotes efficient mating. Their results suggest that Bar1 reshapes the gradient around the MATa cells, enabling them to sharpen the pheromone gradient, move away from other MATa cells to reduce same-sex encounters, and search a larger area to find appropriate mates of the opposite sex. The maintenance and detection of signaling gradients are critical for proper development and cell migration. In single-cell organisms, gradient detection allows cells to orient toward a distant mating partner or nutrient source. Budding yeast expand their growth toward mating pheromone gradients through a process known as chemotropic growth. MATα cells secrete α-factor pheromone that stimulates chemotropism and mating differentiation in MATa cells and vice versa. Paradoxically, MATa cells secrete Bar1, a protease that degrades α-factor and that attenuates the mating response, yet is also required for efficient mating. We observed that MATa cells avoid each other during chemotropic growth. To explore this behavior, we developed a computational platform to simulate chemotropic growth. Our simulations indicated that the release of Bar1 enabled individual MATa cells to act as α-factor sinks. The simulations suggested that the resultant local reshaping of pheromone concentration created gradients that were directed away from neighboring MATa cells (self-avoidance) and that were increasingly amplified toward partners of the opposite sex during elongation. The behavior of Bar1-deficient cells in gradient chambers and mating assays supported these predictions from the simulations. Thus, budding yeast dynamically remodel their environment to ensure productive responses to an external stimulus and avoid nonproductive cell-cell interactions.