ABSTRACT
A 14-mer α-pheromone peptide of
Candida albicans
was chemically synthesized and used to analyze the role of white-opaque switching in the mating process. The α-pheromone peptide blocked cell multiplication and induced “shmooing” in
a/a
cells expressing the opaque-phase phenotype but not in
a/a
cells expressing the white-phase phenotype. The α-pheromone peptide induced these effects at 25°C but not at 37°C. An analysis of mating-associated gene expression revealed several categories of gene regulation, including (i)
MTL
-homozygous-specific, pheromone stimulated, switching-independent (
CAG1
and
STE4
); (ii) mating type-specific, pheromone-induced, switching-independent (
STE2
); and (iii) pheromone-induced, switching-dependent (
FIG1
,
KAR4
, and
HWP1
). An analysis of switching-regulated genes revealed an additional category of opaque-phase-specific genes that are downregulated by α-pheromone only in
a/a
cells (
OP4
,
SAP1
, and
SAP3
). These results demonstrate that α-pheromone causes shmooing, the initial step in the mating process, only in
a/a
cells expressing the opaque phenotype and only at temperatures below that in the human host. These results further demonstrate that although some mating-associated genes are stimulated by the α-pheromone peptide in both white- and opaque-phase cells, others are stimulated only in opaque-phase cells, revealing a category of gene regulation unique to
C. albicans
in which α-pheromone induction requires the white-opaque transition. These results demonstrate that in
C. albicans
, the mating process and associated gene regulation must be examined within the context of white-opaque switching.
