Abstract
Mating pheromone signaling is essential for conjugation between haploid cells of P-type (P-cells) and haploid cells of M-type (M-cells) in Schizosaccharomyces pombe. A peptide pheromone, M-factor, produced by M-cells is recognized by the receptor of P-cells. An M-factor-less mutant, in which the M-factor-encoding genes are deleted, is completely sterile. In liquid culture, sexual agglutination was not observed in the mutant, but it could be recovered by adding exogenous synthetic M-factor, which stimulated expression of the P-type-specific cell adhesion protein, Map4. Exogenous M-factor, however, failed to recover the cell fusion defect in the M-factor-less mutant. When M-factor-less cells were added to a mixture of wild-type P- and M-cells, marked cell aggregates were formed. Notably, M-factor-less mutant cells were also incorporated in these aggregates. In this mixed culture, P-cells conjugated preferentially with M-cells secreting M-factor, and rarely with M-factor-less M-cells. The kinetics of mating parameters in liquid culture revealed that polarized growth commenced from the contact region of opposite mating-type cells. Taken together, these findings indicate that M-factor at a low concentration induces adhesin expression, leading to initial cell-cell adhesion in a type of “distal pheromone action”, but M-factor that is secreted directly in the proximity of the adhered P-cells may be necessary for cell fusion in a type of “proximal pheromone action”.
Highlights
Mating pheromones in ascomycete fungi play an important role in conjugation [1]
Conjugation of S. pombe in liquid medium starts with sexual cell agglutination in response to mating pheromone secreted by cells of the opposite mating type [21]
To investigate the biological roles of M-factor pheromone in the conjugation process, we used an M-factor-less mutant, FS55 (Table 1) [16], in a cell agglutination assay. This homothallic strain showed no cell agglutination, suggesting that M-factor is essential for cell-cell adhesion between P- and M-cells
Summary
Mating pheromones in ascomycete fungi play an important role in conjugation [1]. A partner cell senses a gradient of pheromone and extends a mating projection towards the center of the pheromone source [7]. Another function of pheromones is to choose the most favorable partner who produces the pheromone in abundance [8]. Mating pheromones are recognized by cognate receptors. Specific molecular recognition between a peptide pheromone and its cognate receptor serves as a barrier preventing interspecific hybridization, and plays an important role in reproductive isolation
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