Premium
RAS1 regulates filamentation, mating and growth at high temperature of Cryptococcus neoformans
Author(s) -
Alspaugh J. Andrew,
Cavallo Lora M.,
Perfect John R.,
Heitman Joseph
Publication year - 2000
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2000.01852.x
Subject(s) - cryptococcus neoformans , biology , mutant , microbiology and biotechnology , virulence , mating type , mating , filamentation , gene , phenotype , signal transduction , population , wild type , mating of yeast , genetics , laser , physics , demography , optics , sociology
Cryptococcus neoformans is a basidiomycete yeast and opportunistic human pathogen of increasing clinical importance due to the increasing population of immunocompromised patients. To further investigate signal transduction cascades regulating fungal pathogenesis, we have identified the gene encoding a RAS homologue in this organism. The RAS1 gene was disrupted by transformation and homologous recombination. The resulting ras1 mutant strain was viable, but failed to grow at 37°C, and exhibited significant defects in mating and agar adherence. The ras1 mutant strain was also avirulent in an animal model of cryptococcal meningitis. Reintroduction of the wild‐type RAS1 gene complemented these ras1 mutant phenotypes and restored virulence in animals. A dominantly active RAS1 mutant allele, RAS1 Q67L , induced a differentiation phenotype known as haploid fruiting, which involves filamentation, agar invasion and sporulation in response to nitrogen deprivation. The ras1 mutant mating defect was suppressed by overexpression of MAP kinase signalling elements and partially suppressed by exogenous cAMP. Additionally, cAMP also suppressed the agar adherence defect of the ras1 mutant. However, the ability of the ras1 mutant strain to grow at elevated temperature was not restored by cAMP or MAP kinase overexpression. Our findings support a model in which RAS1 signals in C. neoformans through cAMP‐dependent, MAP kinase, and RAS‐specific signalling cascades to regulate mating and filamentation, as well as growth at high temperature which is necessary for maintenance of infection.