Exploratory polarization facilitates mating partner selection inSaccharomyces cerevisiae

Abstract

Yeast decode pheromone gradients to locate mating partners, providing a model for chemotropism. How yeast polarize toward a single partner in crowded environments is unclear. Initially, cells often polarize in unproductive directions, but then they relocate the polarity site until the polarity sites of two partners align, whereupon the cells "commit" to each other by stabilizing polarity to promote fusion. Here we address the role of the early mobile polarity sites. We found that commitment by either partner failed if just one partner was defective in generating, orienting, or stabilizing its mobile polarity sites. Mobile polarity sites were enriched for pheromone receptors and G proteins, and we suggest that such sites engage in an exploratory search of the local pheromone landscape, stabilizing only when they detect elevated pheromone levels. Mobile polarity sites were also enriched for pheromone secretion factors, and simulations suggest that only focal secretion at polarity sites would produce high pheromone concentrations at polarity site of the partner, triggering commitment.

Optogenetic control of pheromone gradients reveals functional limits of mating behavior in budding yeast

“…Thus, our results explain why elongated MATa chemotropism is rarely observed as directed matesearching in mating reactions with sparse populations. Indeed, depending on the levels of Bar1, within environments crowded with α-factor emitters, cells will either restrict pheromone levels to the emitter vicinity and rely on local mechanisms 7,37 or exhibit random elongation due to gradient overlapping (Fig. 6H).…”