The G-Protein β Subunit GPB1 Is Required for Mating and Haploid Fruiting in Cryptococcus neoformans

Abstract

Cryptococcus neoformans is an opportunistic fungal pathogen with a defined sexual cycle. The gene encoding a heterotrimeric G-protein β subunit, GPB1, was cloned and disrupted.gpb1 mutant strains are sterile, indicating a role for this gene in mating. GPB1 plays an active role in mediating responses to pheromones in early mating steps (conjugation tube formation and cell fusion) and signals via a mitogen-activated protein (MAP) kinase cascade in both MATα and MATa cells. The functions of GPB1 are distinct from those of the Gα protein GPA1, which functions in a nutrient-sensing cyclic AMP (cAMP) pathway required for mating, virulence factor induction, and virulence.gpb1 mutant strains are also defective in monokaryotic fruiting in response to nitrogen starvation. We show thatMATa cells stimulate monokaryotic fruiting of MATα cells, possibly in response to mating pheromone, which may serve to disperse cells and spores to locate mating partners. In summary, the Gβ subunit GPB1 and the Gα subunit GPA1 function in distinct signaling pathways: one (GPB1) senses pheromones and regulates mating and haploid fruiting via a MAP kinase cascade, and the other (GPA1) senses nutrients and regulates mating, virulence factors, and pathogenicity via a cAMP cascade.

ACKNOWLEDGMENTS

We thank Cristl Arndt, Lora Cavallo, and Wiley Schell for assistance; Maria Cardenas for advice; Andy Alspaugh, Maria Cardenas, Cristina Cruz, Rob Davidson, Danny Lew, and Rey Sia for comments; and Andy Alspaugh, Rob Davidson, Don Nuss, and Brian Wickes for reagents and strains.

This work was supported by NIAID R01 grants AI39115 and AI42159 and program project grant P01 AI44975 from NIAID to the Duke University Mycology Research Unit. Joseph Heitman is an associate investigator of the Howard Hughes Medical Institute and a Burroughs Wellcome Scholar in Molecular Pathogenic Mycology.