Asymmetry in Sexual Pheromones Is Not Required for Ascomycete Mating

BACKGROUND We investigated the determinants of sexual identity in the budding yeast Saccharomyces cerevisiae. The higher fungi are divided into the ascomycetes and the basidiomycetes. Most ascomycetes have two mating types: one (called α in yeasts and MAT1-1 in filamentous fungi) produces a small, unmodified, peptide pheromone, and the other (a in yeasts and MAT1-2 in filamentous fungi) produces a peptide pheromone conjugated to a C-terminal farnesyl group that makes it very hydrophobic. In the basidiomycetes, all pheromones are lipid-modified, and this difference is a distinguishing feature between the phyla. We asked whether the asymmetry in pheromone modification is required for successful mating in ascomycetes. RESULTS We cloned receptor and pheromone genes from a filamentous ascomycete and a basidiomycete and expressed these in the budding yeast, Saccharomyces cerevisiae, to generate novel, alternative mating pairs. We find that two yeast cells can mate even when both cells secrete a-like or α-like peptides. Importantly, this is true regardless of whether the cells express the a- or α-mating-type loci, which control the expression of other, sex-specific genes, in addition to the pheromones and pheromone receptors. CONCLUSIONS We demonstrate that the asymmetric pheromone modification is not required for successful mating of ascomycete fungi and confirm that, in budding yeast, the primary determinants of mating are the specificity of the receptors and their corresponding pheromones.

[1]  T. Fowler,et al.  Multiple sex pheromones and receptors of a mushroom-producing fungus elicit mating in yeast. , 1999, Molecular biology of the cell.

[2]  G. Fink,et al.  Two genes required for cell fusion during yeast conjugation: evidence for a pheromone-induced surface protein , 1987, Molecular and cellular biology.

[3]  S. Michaelis,et al.  Biogenesis of the Saccharomyces cerevisiae Mating Pheromone a-Factor , 1997, The Journal of cell biology.

[4]  J. Becker,et al.  Significance of C-terminal cysteine modifications to the biological activity of the Saccharomyces cerevisiae a-factor mating pheromone , 1991, Molecular and cellular biology.

[5]  Joseph Heitman,et al.  The Evolution of Sex: a Perspective from the Fungal Kingdom , 2010, Microbiology and Molecular Biology Reviews.

[6]  K. Thorn,et al.  Optimized cassettes for fluorescent protein tagging in Saccharomyces cerevisiae , 2004, Yeast.

[7]  A. Vershon,et al.  Localization and Signaling of GβSubunit Ste4p Are Controlled by a-Factor Receptor and thea-Specific Protein Asg7p , 2000, Molecular and Cellular Biology.

[8]  G. Ladds,et al.  The sxa2‐dependent inactivation of the P‐factor mating pheromone in the fission yeast Schizosaccharomyces pombe , 1996, Molecular microbiology.

[9]  Brynne C. Stanton,et al.  Allelic Exchange of Pheromones and Their Receptors Reprograms Sexual Identity in Cryptococcus neoformans , 2010, PLoS genetics.

[10]  J. Thorner,et al.  Saccharomyces cerevisiae STE6 gene product: a novel pathway for protein export in eukaryotic cells. , 1989, The EMBO journal.

[11]  G. Sprague,,et al.  Autocrine activation of the pheromone response pathway in matα2- cells is attenuated by SST2- and ASG7-dependent mechanisms , 2003, Molecular Genetics and Genomics.

[12]  J. Haber.  Mating-type gene switching in Saccharomyces cerevisiae. , 1992, Trends in genetics : TIG.

[13]  D. Redecker,et al.  Glomalean fungi from the Ordovician. , 2000, Science.

[14]  G. Sprague,,et al.  Pheromones and pheromone receptors are the primary determinants of mating specificity in the yeast Saccharomyces cerevisiae. , 1989, Genetics.

[15]  S. Pöggeler,et al.  Pheromones and Pheromone Receptors Are Required for Proper Sexual Development in the Homothallic Ascomycete Sordaria macrospora , 2006, Genetics.

[16]  J. Heitman,et al.  Sex in fungi: molecular determination and evolutionary implications. , 2007 .

[17]  K. Arai,et al.  Common signal transduction system shared by STE2 and STE3 in haploid cells of Saccharomyces cerevisiae: autocrine cell‐cycle arrest results from forced expression of STE2 , 1987, The EMBO journal.

[18]  L. Casselton,et al.  Molecular Genetics of Mating Recognition in Basidiomycete Fungi , 1998, Microbiology and Molecular Biology Reviews.

[19]  J. Heitman,et al.  Sexual reproduction between partners of the same mating type in Cryptococcus neoformans , 2005, Nature.

[20]  J. Heitman,et al.  Same-sex mating and the origin of the Vancouver Island Cryptococcus gattii outbreak , 2005, Nature.

[21]  E. Kothe,et al.  Basidiomycete Mating Type Genes and Pheromone Signaling , 2010, Eukaryotic Cell.

[22]  A. Johnson,et al.  Molecular mechanisms of cell-type determination in budding yeast. , 1995, Current opinion in genetics & development.

[23]  G. Saari,et al.  The Saccharomyces cerevisiae BAR1 gene encodes an exported protein with homology to pepsin. , 1988, Proceedings of the National Academy of Sciences of the United States of America.

[24]  Leland H. Hartwell,et al.  Courtship in S. cerevisiae: Both cell types choose mating partners by responding to the strongest pheromone signal , 1990, Cell.

[25]  R. K. Chan,et al.  Physiological characterization of Saccharomyces cerevisiae mutants supersensitive to G1 arrest by a factor and alpha factor pheromones , 1982, Molecular and cellular biology.

[26]  D. Botstein,et al.  The cost of gene expression underlies a fitness trade-off in yeast , 2009, Proceedings of the National Academy of Sciences.

[27]  F. Lottspeich,et al.  Pheromones trigger filamentous growth in Ustilago maydis. , 1994, The EMBO journal.

[28]  R. Lehmann,et al.  An ABC Transporter Controls Export of a Drosophila Germ Cell Attractant , 2009, Science.

[29]  M. Whiteway,et al.  Barrier Activity in Candida albicans Mediates Pheromone Degradation and Promotes Mating , 2007, Eukaryotic Cell.

[30]  G. Sprague,,et al.  Identification and regulation of a gene required for cell fusion during mating of the yeast Saccharomyces cerevisiae , 1987, Molecular and cellular biology.

[31]  T. Hughes,et al.  Signaling and circuitry of multiple MAPK pathways revealed by a matrix of global gene expression profiles. , 2000, Science.

[32]  R. Bennett,et al.  Homothallic and heterothallic mating in the opportunistic pathogen Candida albicans , 2009, Nature.

[33]  B. Nelson,et al.  Asg7p-Ste3p Inhibition of Pheromone Signaling: Regulation of the Zygotic Transition to Vegetative Growth , 2000, Molecular and Cellular Biology.

[34]  M. Bölker,et al.  The a mating type locus of U. maydis specifies cell signaling components , 1992, Cell.

[35]  A. Burt,et al.  Population genomics of the wild yeast Saccharomyces paradoxus: Quantifying the life cycle , 2008, Proceedings of the National Academy of Sciences.

[36]  M. Nowrousian,et al.  Functional Characterization of MAT1-1-Specific Mating-Type Genes in the Homothallic Ascomycete Sordaria macrospora Provides New Insights into Essential and Nonessential Sexual Regulators , 2010, Eukaryotic Cell.

[37]  J. Heitman,et al.  Transitions in Sexuality: Recapitulation of an Ancestral Tri- and Tetrapolar Mating System in Cryptococcus neoformans , 2008, Eukaryotic Cell.

[38]  S. Pöggeler,et al.  Functional Characterization of an α-Factor-Like Sordaria macrospora Peptide Pheromone and Analysis of Its Interaction with Its Cognate Receptor in Saccharomyces cerevisiae , 2005, Eukaryotic Cell.

[39]  G. Sprague,,et al.  Yeast peptide pheromones, a-factor and α-factor, activate a common response mechanism in their target cells , 1986, Cell.

[40]  Peter Walter,et al.  Prm1p, a Pheromone-Regulated Multispanning Membrane Protein, Facilitates Plasma Membrane Fusion during Yeast Mating , 2000, The Journal of cell biology.

[41]  U. Kües.  Life History and Developmental Processes in the Basidiomycete Coprinus cinereus , 2000, Microbiology and Molecular Biology Reviews.