A conserved mitogen‐activated protein kinase pathway is required for mating in Candida albicans

Abstract

SummaryCandida albicans had been thought to lack a mating process until the recent discovery of a mating typelike locus and mating between MTLa and MTL a a a a strains. To elucidate the molecular mechanisms that regulate mating in C. albicans , we examined the function of Cph1 and its upstream mitogen-activated protein (MAP) kinase pathway in mating, as they are homologues of the pheromone-responsive MAP kinase pathway in Saccharomyces cerevisiae . We found that overexpressing CPH1 in MTLa , but not in MTLa/ a a a a strains, induced the transcription of orthologues of S. cerevisiae pheromone-induced genes and also increased mating efficiency. Furthermore, cph1 and hst7 mutants were completely defective in mating, and cst20 and cek1 mutants showed reduced mating efficiency, as in S. cerevisiae . The partial mating defect in cek1 results from the presence of a functionally redundant MAP kinase, Cek2. CEK2 complemented the mating defect of a fus3 kss1 mutant of S. cerevisiae and was expressed only in MTLa or MTL a a a a , but not in MTLa/ a a a a cell types. Moreover, a cek1 cek2 double mutant was completely defective in mating. Our data suggest that the conserved MAP kinase pathway regulates mating in C. albicans . We also observed that C. albicans mating efficiency was greatly affected by medium composition, indicating the potential involvement of nutrient-sensing pathways in mating in addition to the MAP kinase pathway.

The Same Receptor, G Protein, and Mitogen-activated Protein Kinase Pathway Activate Different Downstream Regulators in the Alternative White and Opaque Pheromone Responses ofCandida albicans

“…These results were consistent with those obtained with null mutants of KSS1 and FUS3, the respective orthologues of CEK1 and CEK2, in S. cerevisiae (Elion et al, 1991), and they confirm and extend earlier observations by Chen et al (2002) on cek1⌬, cek2⌬, and the cek1⌬ cek2⌬ double mutant of C. albicans strain CAI4, in which complementation was used between auxotrophic a and ␣ strains as an assay for mating.…”

“…The complemented strain cph1⌬/CPH1 reacquired these responses (data not shown). These results support and extend earlier observations by Magee et al (2002) and Chen et al (2002) in which complementation between auxotrophs was used as an assay to demonstrate that mating depends on CPH1 function.…”

“…The pathogenic yeast Candida albicans also uses MAP kinase pathways in the mating process (Chen et al, 2002;Magee et al, 2002), filamentation (Liu et al, 1994;Csank et al, 1998;Navarro-Garcia et al, 1998), and osmoregulation (Alonso-Monge et al, 1999;Smith et al, 2004). But C. albicans has one additional and unique response to mating pheromones that so far has not been identified in other yeast .…”

“…These alternative signals are then transduced through the same heterotrimeric G protein to activate the same MAP kinase pathway, which in turn activates the same downstream regulators that elicit similar mating responses, including G1 arrest, polarization, and shmooing (Sprague et al, 1983;Bender and Sprague, 1986;Leberer et al, 1997). Other fungi, including Magnaporthe grisea (Dixon et al, 1999;Zhao et al, 2005b) Neurospora crassa (Li et al, 2005), and Cryptococcus neoformans (Davidson et al, 2003;Kraus et al, 2003;Bahn et al, 2005) also use MAP kinase pathways for a variety of responses (Kruppa and Calderone, 2006).The pathogenic yeast Candida albicans also uses MAP kinase pathways in the mating process (Chen et al, 2002;Magee et al, 2002), filamentation (Liu et al, 1994;Csank et al, 1998;Navarro-Garcia et al, 1998), and osmoregulation (Alonso-Monge et al, 1999;Smith et al, 2004). But C. albicans has one additional and unique response to mating pheromones that so far has not been identified in other yeast .…”

“…These changes have been demonstrated, at least in vitro, to result in a thicker white cell biofilm that provides a protective environment for spontaneously arising opaque cells to undergo mating Soll and Daniels, 2007). Although mutational studies using complementation of auxotrophic traits as an assay for mating indicated that the ␣-receptor Ste2p; the MAP kinases Cek1p and Cek2p, homologues of S. cerevisiae Kss1p and Fus3p; and a key target transcription factor, Cph1p, the homologue of S. cerevisiae Ste12p, were necessary for mating in C. albicans a/a cells (Chen et al, 2002;Magee et al, 2002;Bennett et al, 2003), the receptors, signal transduction pathways, and downstream transcription factor(s) that mediate the unique white cell response to pheromone remained unknown.There existed at least three possible scenarios for this pathway. First, the same receptor, G protein complex, MAP kinase pathway, and targeted transcription factor could mediate both the opaque cell mating response and the white response.…”