Molecular coevolution of a sex pheromone and its receptor triggers reproductive isolation in Schizosaccharomyces pombe

Abstract

The diversification of sex pheromones is regarded as one of the causes of prezygotic isolation that results in speciation. In the fission yeast Schizosaccharomyces pombe, the molecular recognition of a peptide pheromone by its receptor plays an essential role in sexual reproduction. We considered that molecular coevolution of a peptide-mating pheromone, M factor, and its receptor, Map3, might be realized by experimentally diversifying these proteins. Here, we report the successful creation of novel mating-type pairs by searching for map3 suppressor mutations that rescued the sterility of M-factor mutants that were previously isolated. Several strong suppressors were found to also recognize WT M factor. The substituted residues of these Map3 suppressors were mapped to F204, F214, and E249, which are likely to be critical residues for M-factor recognition. These critical residues were systematically substituted with each of the other amino acids by in vitro mutagenesis. Ultimately, we successfully obtained three novel mating-type pairs constituting reproductive groups. These novel mating-type pairs could not conjugate with WT maters. Furthermore, no flow of chromosomally integrated drug-resistance genes occurred between the novel and the WT mating pairs, showing that each experimentally created reproductive group [e.g., M factor(V5H) and Map3(F214H)] was isolated from the WT group. In conclusion, we have succeeded in creating an artificial reproductive group that is isolated from the WT group. In keeping with the biological concept of species, the artificial reproductive group is a new species.fission yeast | mating pheromone | G-protein-coupled receptor | reproductive isolation | speciation S peciation is the most critical step in evolution (1). A new species branches off from an original species when a group of individuals is isolated reproductively (termed "reproductive isolation") (2). Chemical communication between the two sexes is important in both attracting individuals of the opposite sex and the courtship reaction. Pheromone diversification may be a possible mechanism underlying reproductive isolation.Female-attracting peptide pheromones of newts are providing a promising means to explore this mechanism. A decapeptide called sodefrin was first identified during the analysis of a cDNA library of the abdominal gland of the red-bellied newt Cynops pyrrhogaster (3, 4). A closely related newt, the sword-tailed newt Cynops ensicauda, produces a similar peptide pheromone named Silefrin (5). Interestingly, a sodefrin variant, aonirin, was found in the Nara area of Japan; 1 of 10 amino acids in aonirin differs from those in sodefrin, the prototype peptide (Table 1) (6). This variant peptide was found to not be effective in attracting females in the Niigata and Chiba areas of Japan (7). It was, thus, speculated that altering the primary structure of the female-attracting peptide of the red-bellied newt and coevolution of the corresponding receptor protein may lead to reproductive isolation. To verify this speculati...

Experimental Evolution of Species Recognition

“…Haploid cells locate mating partners by polarizing their growth in the direction of the highest pheromone concentration [11,12]. Mutations in either pheromones or receptors can alter mating efficiency [13][14][15], and pheromone-receptor specificity has been proposed as a possible mechanism for mate discrimination between those species whose pheromone peptide sequences differ [3,16]. Attraction to pheromones produced by incompatible partners is particularly costly for yeast because each cell can mate only once; zygote inviability or sterility is equivalent to death for the mating haploids.…”

The asymmetric chemical structures of two mating pheromones reflect their differential roles in mating of fission yeast

“…The quantitative assay was performed as described previously (Seike et al, 2013). Heterothallic haploid strains carrying a different drug-resistance marker (kanMX6, hphMX6, or natMX6) on their chromosomes (Seike et al, 2015;Seike et al, 2019) were mixed and then incubated in SSL−N medium for 2 days to induce mating. The cell suspension was diluted and spread on plates containing the appropriate combinations of drugs.…”

The natural diversity and ecology of fission yeast

“…Natural isolates also vary genetically at mating type regions and in their mating behavior, with some strains mutating more frequently from h + to h − and vice versa (Schlake & Gutz, ). In an interesting demonstration that reproductive isolation could evolve via pre‐zygotic mechanisms, Seike, Nakamura, and Shimoda () created three novel reproductive groups with different pheromone–receptor pairs. Given these changes it is likely that pre‐zygotic reproductive isolation occurs within some populations.…”