Role Of The Mpk1 MAP Kinase And Polarism Components In Yeast Mating

In the yeast Saccharomyces cerevisiae many cellular responses to extracellular signal require the output of more than one signal transduction cascade. The coordination of the mating pheromone response pathway and the cell wall integrety MAP kinase pathway during yeast mating serves as a good example of different signaling pathways regulating same cellular response. The mating pathway stimulates the formation of mating projections oriented toward the gradient of mating pheromone secreted by a mating partner and, during which, the cell wall integrety MAP kinase pathway is activated which is required for new cell wall synthesis during projection formation.The polarity proteins Spa2p, Pea2p and Bni1p were found to participate in crucial steps of bud morphogenesis, septation, and polarized growth to form buds or mating projections. Mating pheromone disfavorise the formation of the neck constriction, promoting shmoo formation. The cell integrity pathway, which controls new cell wall synthesis, was found to be necessary for cell viability during projection formation.The yeast protein kinase C homolog, Pkc1p, acts upstream of the cell wall integrity MAK kinase cascade. Which is composed of Bck1p, the MAPKKK, the functional redundant MAPKK, Mkk1p and Mkk2p, and the Mpk1p MAP kinase. This pathway plays an essential role in regulating cell wall integrity in response to many extracellular stimuli and also participates in growth control and cell cycle regulation. Furthermore, researches in our laboratory demonstrated that during mating Afr1p mediates pheromone-induced activation of the Mpk1p protein, which is required for mating projection formation and efficient mating.This study focused on looking for direct evidence that an adequate level of Mpk1 activation is crucial for mating efficiency. To establish an interrelationship between projection formation and Mpk1p activation in terms of their role in promote efficient mating, we investigated cells deficient in components of the mating and cell integrity pathways, by constructing different strains harboring single deletions in the SPA2, BNI1 and PEA2 genes and double deletions in the SPA2 MKK2, BNI1 MKK2 and PEA2 MKK2 genes. The mating efficiency of these strains was determined. Also, the Mpk1p MAP Kinase pathway activation was analysed by determining the phospho-Mpk1 protein level under mating pheromone induction. Our results demonstrated that the mating defect of the spa2Δ, pea2Δand bni1Δmutants is not only due to their defects in forming acute mating projections, but also to overactivation of the Mpk1p MAP kinase in those mutants under pheromone induction.