Cell cycle-dependent and independent mating blocks ensure fungal zygote survival and ploidy maintenance

To ensure genome stability, sexually reproducing organisms require that mating brings together exactly 2 haploid gametes and meiosis occurs only in diploid zygotes. In the fission yeast Schizosaccharomyces pombe , fertilization triggers Mei3-Pat1-Mei2 signaling cascade, which represses subsequent initiates meiosis. Here, we establish a degron system to specifically degrade proteins postfusion demonstrate blocks not safeguard zygote ploidy but also prevent lysis caused by aberrant fusion attempts. Using long-term imaging flow-cytometry approaches, identify previously unrecognized independent roles for Mei3 Mei2 We show promotes premeiotic S-phase independently of cell cycle progression is both necessary sufficient reduce zygotic behaviors. imposes meiotic program cycle, behaviors progression. Thus, find fungi preserve survival at least mechanisms where fate imposed reentry triggered synergize mating.