Previous Article | Next Article 
Journal of Bacteriology, May 1999, p. 3058-3068, Vol. 181, No. 10
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Role of the Mitogen-Activated Protein Kinase Hog1p
in Morphogenesis and Virulence of Candida albicans
R.
Alonso-Monge,
F.
Navarro-García,
G.
Molero,
R.
Diez-Orejas,
M.
Gustin,
J.
Pla,*
M.
Sánchez, and
C.
Nombela
Departamento de Microbiología II, Facultad de
Farmacia, Universidad Complutense de Madrid, E-28040 Madrid, Spain
Received 9 December 1998/Accepted 11 March 1999
 |
ABSTRACT |
The relevance of the mitogen-activated protein (MAP) kinase Hog1p
in Candida albicans was addressed through the
characterization of C. albicans strains without a
functional HOG1 gene. Analysis of the phenotype of
hog1 mutants under osmostressing conditions revealed that
this mutant displays a set of morphological alterations as the result
of a failure to complete the final stages of cytokinesis, with parallel
defects in the budding pattern. Even under permissive conditions,
hog1 mutants displayed a different susceptibility to some
compounds such as nikkomycin Z or Congo red, which interfere with cell
wall functionality. In addition, the hog1 mutant displayed a colony morphology different from that of the wild-type strain on some
media which promote morphological transitions in C. albicans. We show that C. albicans hog1 mutants are
derepressed in the serum-induced hyphal formation and, consistently
with this behavior, that HOG1 overexpression in
Saccharomyces cerevisiae represses the pseudodimorphic transition. Most interestingly, deletion of HOG1 resulted
in a drastic increase in the mean survival time of systemically
infected mice, supporting a role for this MAP kinase pathway in
virulence of pathogenic fungi. This finding has potential implications
in antifungal therapy.
| |
INTRODUCTION |
Fungi, like all living organisms,
must be able to respond to changes in environmental conditions and
hence develop a response which enables their adaptation to the new
physiological situation. Signal transduction pathways serve as a
molecular mechanism to accomplish this cellular response. In
Saccharomyces cerevisiae, a model eukaryotic cell system,
some of these pathways involve members of the MAP kinase family (from
mitogen-activated protein kinase), a set of enzymes performing
essential functions in cell physiology first discovered in mammalian
cells but later shown to be also present in lower eukaryotes (3,
12). Among these, the high-osmolarity glycerol (HOG) response
pathway (6) allows adaptation to high-osmolarity conditions
and seems to be especially important in terms of ecological adaptation.
This latter route is triggered in response to high external osmolarity
(i.e., low water activity) and results in the accumulation of glycerol
as an intracellular compatible solute in S. cerevisiae.
Several elements of this cascade have been identified in recent years
(see reference 3 for a recent review). The initial
triggering events in the cascade are initiated by at least two
different pathways (43): the first one involves Sln1p
(58), Ypd1 (65), Ssk1, and Ssk2p/Ssk22p kinases
(44), while the second involves Sho1p, a putative membrane protein able to interact with, and activate, the Pbs2p MAP kinase kinase via Ste11p (43, 64) and possibly Ste20p/Ste50p
(57). Both signals converge at the Pbs2p level, which in
turn phosphorylates and activates Hog1p, which mediates the
intracellular accumulation of osmolytes such as glycerol
(4). This response also involves reorganizations of the
cytoskeleton (11) and, presumably, cell wall modifications,
as suggested by the involvement of PBS2 in 
-(1,6)-glucan
assembly (27, 35). Therefore, the HOG pathway participates in a pleiotropic response that enables a correct and rapid
adaptation to osmotic stress. Functionally homologue-related cascades
have been found in other fungal systems such as the fission yeast
Schizosaccharomyces pombe. Interestingly, in this organism, this route not only is restricted to osmoadaptation but also links cell
cycle control and sexual development (70, 71).
Candida albicans is a pathogenic yeast of great clinical
interest in view of the increasing incidence of the infection that it
causes in immunocompromised individuals (55). In addition, its ability to switch between a yeast-like and a hyphal form of growth
has long been suspected to play a role in virulence (13, 30,
56). C. albicans has therefore been chosen as a model of pathogenic dimorphic fungi, although its diploid nature and lack of
a sexual cycle have hampered molecular genetic studies, which have
relied mostly on S. cerevisiae, a nonpathogenic yeast, as a
host organism (62, 68). Knowledge of signal transduction pathways in pathogenic fungi is essential not only to understand their
mechanisms of adaptation to a complex and changing environment such as
the human body (and, therefore, their virulence) but also as a way to
identify potential novel targets in antifungal therapy. In C. albicans, some genes homologous to the mating or pseudohyphal pathway genes (32, 36, 46, 72, 73, 77) or PKC1
pathway (53, 60) have been identified in recent years. We
have previously described the isolation of the C. albicans
gene homologue of the S. cerevisiae HOG1 gene (designated
HOG1Ca, previously) and shown its involvement in
osmoadaptation by increasing the internal glycerol content upon osmotic
stress (67). In the present work, we characterize the
phenotype of C. albicans hog1 mutants, showing their defects in the last stages of cytokinesis and cell wall biogenesis and repositioning certain elements of the budding machinery after osmotic
stress. In addition, we show that the HOG pathway represses the
serum-induced yeast-to-hypha transition in C. albicans and describe its role as a major determinant of virulence. These results suggest an additional role for this MAP kinase pathway in pathogenic fungi.
| |
MATERIALS AND METHODS |
Strains and growth conditions.
The yeast and bacterial
strains used in this study are listed in Table
1. For clarity and unless otherwise
stated, the designation hog1 will always indicate the
homozygous hog1/hog1 Ura+ strain (strain CNC13).
Although the genotypes of the strains were confirmed by Southern blot
analyses, a control strain integrating the HOG1 gene at the
LEU2 locus was constructed by homologous recombination using
the restriction endonuclease KpnI, thus obtaining strain
CNC15-10. Strain CNCH1 was obtained by integrating a p34H derivative
(constructed by inserting a 1.59-kbp SspI-SspI
fragment from YEP-HISX [63] into the
HindII site of p34H [76]) containing the HIS1 marker at the HIS1 locus in the genome
of CNC15-10 by using NruI as the restriction enzyme. Yeast
strains were grown at 37°C (unless otherwise stated) in YED medium
(1% yeast extract, 2% glucose) or SD minimal medium (2% glucose,
0.67% yeast nitrogen base without amino acids) with the appropriate
auxotrophic requirements (50 µg/ml). The ability of cells to undergo
the yeast-to-hypha transition was tested by using Lee's medium at pH
6.7 (38), SD medium plus 10% (vol/vol) fetal bovine serum,
fetal bovine serum, Spider medium (1% mannitol, 1% nutrient broth,
0.2% K2HPO4, 1.35% agar) (39),
SLAD medium (21), or YED medium plus fetal bovine serum at
1, 5, 10, and 20% as well as whole serum. To check the behavior of
C. albicans strains with respect to dimorphic transition,
cells were inoculated at 105 cells/ml in prewarmed liquid
medium. Growth in liquid medium was estimated as the absorbance at 600 nm (A600) or dry weight; in this case, 10 ml of
the culture was filtered with a 0.45-µm-pore-size filter (Millipore)
and dried at 42°C until a stable weight had been attained. Time lapse
photography was performed, with images taken at defined intervals with
cells deposited onto a thermostabilized chamber at 37°C containing
solid yeast extract-peptone-dextrose (YEPD) medium supplemented with
0.75 M NaCl.
Molecular biology procedures and plasmid constructions.
Standard molecular biology procedures were used (2).
C. albicans was transformed as described previously
(31). The plasmid YEp352 (a URA3 2µm-derived
vector), pHOG1c24.2 (the C. albicans HOG1 gene in YEp352),
and pJB30 (the S. cerevisiae HOG1 gene in a 2µm-derived
vector) have been described previously (25, 67). The
pRM-HOG1 plasmid, an episomic plasmid carrying the C. albicans HOG1 gene and the 5' regulatory regions, was obtained by inserting a HindIII fragment from pHOG1c24.2 into the
SmaI site of pRM1 (63).
Confocal microscopy, flow cytometry, and fluorescent staining
methods.
Cells grown in YED medium plus 1 M NaCl were washed twice
with 0.2 M NaCl and stained with primuline (Sigma, St. Louis, Mo.) at
50 ng/ml (final concentration) for 30 min at 37°C or calcofluor white
(Bayer) at 4 ng/ml (final concentration) for 5 min at room temperature.
Cells were briefly sonicated before the fluorescence was quantified
with a Bio-Rad Bryte HS flow cytometer (for calcofluor white) or a
Becton Dickinson (San José, Calif.) FACScan flow cytometer (for
primuline). The same procedure was used for visualization of chitin
under a Bio-Rad MRC 1000 confocal microscope. For analyses of DNA
content, exponentially growing cells were transferred to YED medium
supplemented or not with 1 M NaCl at 37°C. Aliquots were removed at
defined intervals, collected by low-speed centrifugation, washed with
phosphate-buffered saline (PBS), and resuspended in cold 70% ethanol
for 1 min. They were then washed twice with PBS, resuspended in 500 µl of PBS containing 1 mg of RNase/ml, and incubated for 30 min at
37°C. Cells were briefly sonicated, washed twice with PBS, and
stained with propidium iodide (Sigma) at a final concentration of
0.005% in PBS, and the DNA content was analyzed with a flow cytometer.
Cell viability was assessed by staining the cells with propidium iodide
at 0.005% in PBS.
Electron microscopy.
Cells growing in YED medium at 37°C
were transferred to YED medium supplemented with 1 M NaCl, and samples
were taken at different times. Cells for scanning electron microscopy
were prepared as described previously (75, 78) and
visualized with a JEOL JSM-6400 microscope. Transmission electron
microscopy samples were obtained as described previously
(49) and embedded in Epon 812. Eighty-nanometer-thick sections were observed through a Zeiss 902 microscope from the Centro
de Microscopía Electrónica Luis Bru (Universidad
Complutense de Madrid [UCM]).
Antifungal assays.
MICs were determined by the microdilution
method in 96-well plates as described elsewhere (51, 52) by
using SD medium without uridine. Drop tests were used to check
susceptibility to Congo red and calcofluor white. They were performed
by spotting 105, 104, 103, and
102 cells (in a 10-µl volume) onto YEPD solid medium plus
Congo red or calcofluor white at 100, 120, and 150 µg/ml and
incubated for 24 h at 24, 30, and 37°C for S. cerevisiae or at 30, 37, and 42°C for C. albicans.
Chitinase activity assays.
Chitinase assays were carried out
as described before (34). Hydrolysis of the substrate was
determined after 1 h of incubation at 30°C. Units of activity
are defined as nanomoles of 4-methylumbelliferone (the fluorescent
product of hydrolysis of the substrate by chitinase) released per hour.
Virulence assays.
Virulence assays were performed
essentially as described previously (17).
| |
RESULTS |
Structural alterations in C. albicans hog1
mutants.
To characterize the influence of high solute
concentrations on the structure and morphology of C. albicans and the role of the HOG pathway in C. albicans
under these conditions, we performed a detailed characterization of the
alterations of wild-type and hog1 mutants. For this purpose,
exponentially growing cells in YED medium were diluted and transferred
to hyperosmolar conditions (1 M NaCl) and both the optical density (OD)
and dry weight were measured at regular intervals. This shift to higher
osmolarity caused both wild-type and hog1 cultures to arrest
growth (approximately 3 h for the wild type and 5 h for the
mutants). Both wild-type and hog1 strains resumed growth,
with subsequent doubling times of 2 h for the wild type and 5 h for the hog1 mutants (Fig.
1A). Mutant cells achieved a lower final
OD (5.5 versus 10.1) or mass (4.5 versus 8.0 mg/ml) after 48 h of
growth and entry into stationary phase. These results indicate that the
high osmolarity-induced growth arrest is transient and that despite
being osmosensitive and failing to accumulate glycerol intracellularly
(67), hog1 mutants are still able to grow in
mass.
View larger version (66K):
[in this window]
[in a new window]
|
FIG. 1.
Terminal phenotype of hog1 mutants. (A)
Effect of osmostress (1.0 M NaCl) on the growth of wild-type cells
(SC5314) or the hog1 mutant (CNC13) in liquid YED medium.
The OD (estimated as the A600) is plotted versus
time. The y-axis scale is logarithmic. (B) Propidium
iodide-stained cells of the hog1 mutant after 24 h of
growth under restrictive conditions (right panel). Arrows indicate dead
cells in the clusters observed under phase-contrast microscopy (left
panel). (C) Flow cytometric analysis of the DNA content of mutant
cultures grown in parallel on YED medium or YED medium plus 1 M NaCl.
The peaks observed for control cells (labeled YED 0') represent 2n
(left) and 4n (right) DNA content, while the numbers indicate the time
in minutes after the transfer to the restrictive conditions. (D)
Microscopic analysis of hog1 mutant cells under restrictive
conditions (left panel; phase-contrast image), showing nuclei (right
panel; fluorescence image). The arrow indicates a detail of a nucleus
in the process of segregation to the new bud. A representative cluster
of cells is shown. Bars, 1 µm.
|
|
Cell viability was determined by both flow cytometry quantification of
dead cells stained with propidium iodide (a fluorochrome
able to enter
dead cells due to the loss of selective permeability)
(
16)
and direct standard plating (CFU counting) on YED medium
(data not
shown). Visual microscopic examination was also used
to monitor the
behavior of the culture. No obvious differences
were observed in the
morphology of the wild-type or
hog1 cells
at 2 or 4 h
after the change to the 1 M NaCl medium. However,
after 24 h,
individual mutant cells appeared rounder and smaller
than wild-type
cells (as determined by flow cytometry). At the
same time, several
mutant cells remained attached after budding
due to an apparent defect
in cell separation (Fig.
1B, left panel),
a phenotype not observed in
the wild-type strain (data not shown).
Consistent with the previous
data on growth, cell viability in
the
hog1 culture was high
(more than 75% after 24 h under hyperosmotic
conditions). Dead
cells revealed by propidium iodide uptake had
no specific localization
within the clusters of cells (Fig.
1B,
right panel). The DNA content
was also quantified. Under nonrestrictive
conditions (YED medium
alone),
hog1 cells displayed a DNA pattern
characteristic of
an asynchronous culture (Fig.
1C, left panels),
while on YED medium
plus 1 M NaCl, the peak containing a 2n DNA
content disappeared in 60 min, and after this period, only 4n
cells were detected (Fig.
1C, right
panels). After this period,
the DNA content increased as the result of
normal DNA replication
but failure of the cells to segregate, therefore
appearing as
a single cytometric count. Cells under the microscope
appeared
to have a single nucleus (Fig.
1D). The observed increase in
DNA
content therefore seems to be the result of impaired cell division
and not sensitivity to the high osmolarity of normal DNA replication.
This effect was not observed under permissive conditions or in
osmostressed wild-type cells (data not shown). Interestingly,
some of
the
hog1 cells also displayed altered budding patterns
in
which the polarity of bud emergence was lost, some cells budding
away
from the distal poles (Fig.
2A). Scanning
transmission microscopy
showed that daughter cells were apparently
completely formed but
remained attached to the mother cell, unable to
complete cytokinesis
(Fig.
2A). Transmission electron microscopy (Fig.
2B) revealed
that the septum between the mother and daughter cells was
physically
completed and that the outer cell wall still connected both
cells.
Sonication for different periods of time or digestion with
glusulase
[a
-(1,3)-glucanase enriched lytic preparation] did not
result
in segregation of these clusters, but interestingly, treatment
with a commercial preparation of chitinase did (data not shown).
View larger version (82K):
[in this window]
[in a new window]
|
FIG. 2.
Scanning and transmission electron microscopy of
hog1 mutants. (A) Scanning electron microscopy of
hog1 mutant (CNC13) (left panel) or wild-type (SC5314)
(right panel) cells after 24 h of growth under restrictive
conditions. The arrow indicates a characteristic cell with a symmetric
type of division. (B) Transmission electron microscopy of similar
samples. Arrows indicate almost completely separated but still
connected cells with well-formed septa. Bars, 1 µm.
|
|
The influence of osmostressing conditions on polarity was investigated
in more detail. For this purpose, growing cells were
plated onto YEPD
solid medium supplemented with 0.75 M NaCl and
photographs were taken
at different intervals. While the wild-type
strain was able to grow
normally after a short time of adaptation
to the new physiological
situation (data not shown),
hog1 mutant
cells stopped
growing for a prolonged time. In this mutant, a
small percentage of the
population displayed a defect which consisted
in small newly formed
buds ceasing growth while mother cells emitted
a new bud that completed
its growth. By contrast, during the same
period, the first bud did not
resume growth at all (Fig.
3). These
observations are consistent with the idea that certain components
of
the bud positioning or emergence machinery (but not DNA replication)
are dependent on a functional HOG pathway (
7).
View larger version (119K):
[in this window]
[in a new window]
|
FIG. 3.
Defects in bud site selection after osmotic shock. Time
lapse photography of hog1 mutant cells under solid YPD
medium supplemented with 0.75 M NaCl. Numbers indicate the time (in
hours) after the transfer to restrictive conditions. Arrows labeled
"a" indicate small buds, while the arrow labeled "b" indicates
a newly formed bud. Bars, 1 µm.
|
|
C. albicans hog1 mutants are resistant to certain cell
wall inhibitors.
The susceptibility of C. albicans hog1
mutants to antifungals with different structures and mechanisms of
action was determined. No differences were found between wild-type and
hog1 cell susceptibilities to the following antifungals
under nonosmostressing conditions: cilofungine (an inhibitor of
-glucan biosynthesis; MIC, 1 µg/ml), trichodermine (an inhibitor
of protein synthesis; MIC, 1 µg/ml), fluconazole and miconazole
(inhibitors of ergosterol biosynthesis; MICs, 2.5 and 1 µg/ml,
respectively), canavanine (a toxic amino acid analog; MIC, 6.25 µg/ml), 5-fluorocytosine (an inhibitor of nucleic acid synthesis;
MIC, 0.0625 µg/ml), or amphotericin B (inhibitor of membrane
functionality; MIC, 2.9 µg/ml). However, a drastic difference was
observed in the susceptibilities of hog1 and wild-type cells
to nikkomycin Z, an inhibitor of chitin biosynthesis. When assayed at
30°C, both wild-type and mutant cells displayed high levels of
resistance to nikkomycin Z (MIC, >800 µg/ml). However, when
susceptibility was assayed at 37 or 42°C, the wild type became sensitive (nikkomycin Z MICs, 3.12 µg/ml at 37°C and 0.78 µg/ml at 42°C) but the hog1 strain remained resistant to
nikkomycin Z (MIC, >800 µg/ml). The MICs of nikkomycin Z for the
heterozygous HOG1/hog1 mutant and the wild-type strain,
SC5314, were the same. It should be noted that these effects were
observed under normal conditions, i.e., nonosmostressed cells.
In addition,
C. albicans hog1 cells were consistently more
resistant than the corresponding heterozygous or wild-type strains
to
Congo red, a dye which also interacts with the fungal cell
wall (Fig.
4A) at all the temperatures tested, and
very slightly
to calcofluor white (data not shown). These differences
were not
found in
S. cerevisiae hog1 mutants in two
different backgrounds.
Unexpectedly, overexpression of the
C. albicans HOG1 gene (or
the homologous
S. cerevisiae
HOG1 gene) in
S. cerevisiae by using
an episomal vector
also resulted in increased resistance to these
compounds, especially to
calcofluor white (Fig.
4B).
View larger version (54K):
[in this window]
[in a new window]
|
FIG. 4.
Antifungal susceptibility and cell wall architecture.
(A) Different amounts of cells (indicated at the top of the rows) from
the indicated C. albicans strains were spotted onto YEPD
medium (as a control) or YEPD medium supplemented with Congo red at 150 µg/ml and incubated at 37°C. (B) Experiments similar to those
described for panel A were done with the S. cerevisiae
strains indicated; cells were spotted onto YEPD medium supplemented
with a 150-µg/ml final concentration of calcofluor white and
incubated at 30°C for 24 h. (C) Chitinase activity in cell
extracts after 24 and 48 h of growth under nonrestrictive (1 M
NaCl) (left panel) and restrictive (right panel) conditions. Units of
activity (UA) (see Material and Methods) per milligram of dried extract
are given in the y axis. Data are the mean value of two independent
experiments.
|
|
To further explore the relationship between the cell wall and the
HOG1 gene, the chitin levels in both wild-type and mutant
strains under restrictive (1.0 M NaCl) and nonrestrictive conditions
were quantified by flow cytometry with both calcofluor white and
primuline, but no significant variation in the chitin content
was
observed. In addition, confocal microscopy analyses showed
the
predicted chitin accumulation on scars and mother-bud necks
(data not
shown). In view of the presence of a well-formed septum
between mother
and bud but incomplete cytokinesis in mutant cells,
we measured
chitinase activity in osmostressed cells. As shown
in Fig.
4C, a
significant reduction in the enzymatic activity
of chitinase was
observed in total cell extracts. These results
suggest that the cell
separation defects observed in this mutant
could be the result of
defective chitinase activity. Chitinase
activity has been shown, in
fact, to be required for cell separation
in
S. cerevisiae
(
34), although no dependence on the HOG pathway
has been
described. Collectively, our results suggest a link between
cell wall
metabolism and the HOG pathway in
C. albicans.
A role for HOG1 in morphological transitions.
An
important biological question to be addressed in C. albicans
is its ability to undergo the dimorphic transition, a cell differentiation program that allows yeast cells to generate hyphal forms. Dimorphism, which has long been suspected to play a role in
C. albicans pathogenesis (see reference
56 and references therein), can be induced by
environmental factors such as the pH or the temperature or can be
induced in response to serum, proline, or
N-acetylglucosamine. To analyze the role of HOG1
in these transitions, we observed the colony morphology of
hog1 cells under different growth conditions. First, on
normal YED plates, hog1 cells did not show the limited agar
invasion displayed by SC5314 wild-type cells (Fig.
5). A similar difference was also found
when both strains were plated in Spider medium, which has been
described as inducing hyphal formation (39). Mutant
colonies, although able to invade the agar, appeared smooth with small
grains, while wild-type colonies showed clear invasive borders.
However, the mutant strain observed under an optical microscope
appeared as large filaments, similar to the wild type. Most
interestingly, mutant cells grown on a nitrogen limiting medium such as
SLAD medium (which has been shown to induce pseudohyphal formation in
S. cerevisiae [21]) penetrated the agar
medium and were hence more invasive than wild-type cells (Fig. 5),
frequently appearing under the microscope as short filaments or
pseudohyphae. None of these effects were observed in the heterozygous
strain (strain CNC11) or the strain in which the wild-type
HOG1 gene was reintroduced (data not shown).
View larger version (68K):
[in this window]
[in a new window]
|
FIG. 5.
Colony morphology of hog1 mutants. Colony
morphology of wild-type (SC5314) and mutant hog1 (CNC13)
cells on different solid media. Approximately 50 CFU were spread onto
either YED medium, Spider medium, minimal SD medium plus 10% bovine
fetal serum, or SLAD medium on petri dishes and incubated for 7 days at
37°C before photographs were taken. The colony borders are shown for
cells on Spider medium.
|
|
To explore further the filamentation in
hog1 cells, we
analyzed their behavior in the true dimorphic transition. When assayed
on liquid media that induce hyphal formation, such as Lee's medium
at
pH 6.7 or serum, no significant differences were found between
the
mutant (CNC13), the heterozygous (CNC11 and CNC15-10), and
the
wild-type (SC5314) strains. However, we performed experiments
in which
the cells were exposed to limiting serum concentrations.
On 100%
serum, both mutant and wild-type cells generated long
filaments and no
differences could be observed with respect to
the timing of appearance
of the germinative tubes. In contrast,
on YED medium containing 1, 5, and 10% serum,
hog1 mutant cells
(strain CNC13) displayed a
clear filamentous phenotype, with several
cells appearing as long true
polynucleated filaments with several
septa, the frequency of this
occurrence in wild-type cells (data
not shown) or the heterozygous
strain (CNC11) was much lower (Fig.
6A).
Consistent with this, on solid medium containing 10% bovine
fetal
serum,
hog1 cells (strain CNC13) generated wrinkled colonies
(Fig.
5) with frequent invaginations towards the inner regions
of the
colony that were absent in the wild-type cells. This presumably
regulatory (repressive) role of
HOG1 in morphological
transitions
was also evidenced by the suppression of pseudohyphal
growth in
S. cerevisiae. Overexpression of the
C. albicans HOG1 gene from
a multicopy plasmid partially
suppressed the pseudodimorphic transition
(invasion) of the diploid
S. cerevisiae strain L5366 (Fig.
6B)
on nitrogen-deprived
medium (SLAD medium). These results clearly
support the regulatory role
of the HOG pathway in morphogenetic
programs in
C. albicans.
View larger version (58K):
[in this window]
[in a new window]
|
FIG. 6.
Effect of Hog1p on the serum-induced dimorphic
transition. (A) Cells from the indicated strains were inoculated in YED
medium plus bovine fetal serum at different concentrations (20, 10, 5, and 1%), and phase-contrast microphotographs were taken after 6 h
of incubation at 37°C. (B) Border colony morphologies of S. cerevisiae L5366 transformed with vector YEp352 (left picture) or
the multicopy plasmid pHOG1c24.2 (bearing the C. albicans
HOG1 gene) (right picture) are shown. Cells were plated onto SLAD
medium, and pictures were taken after growth for 6 days at 30°C.
Bars, 10 µm.
|
|
Virulence of hog1 cells in a mouse model.
To
analyze the role of the HOG pathway in virulence, we checked the
behavior of hog1 cells by use of a mouse model of fungal infection. Both BALB/c and DBA/2 mice were challenged with different doses of the parental (SC5314) and a hog1 mutant (CNC13)
strain by inoculation into the lateral vein of the tail. These two
mouse strains have been shown to differ in their susceptibility to
fungal infections, BALB/c mice being more resistant than DBA/2
mice (24). Standard death curves were obtained after the
infection, and representative death curves are shown in Fig.
7. In BALB/c mice, a challenge with a
dose of 106 cells resulted in a rapid mortality for the
wild-type strain (mean survival time [MST] of 3 days). In contrast,
mice challenged with hog1 cells showed a drastic decrease in
mortality, being able to survive up to 60 days (Fig. 7A). These
differences were also observed for mice given a larger inoculum
(107 blastospores) (Fig. 7B), with MSTs of 1 day for the
wild-type strain and 30 days for the mutant (see also Table 2). A lower dose (105 blastospores) did not lead to any differences in
the mortality of mice challenged with either yeast strain.
View larger version (18K):
[in this window]
[in a new window]
|
FIG. 7.
Virulence assays. Standard survival curves of BALB/c
mice infected systemically with 106 (A) or 107
(B) cells of the C. albicans strains indicated in the
figure. Since strains CNC15-10, RM100, and CNCH1 at a dose of
107 gave curves similar to the one shown for SC5314 in
panel B, these results are therefore not shown for clarity.
|
|
DBA/2 mice were similarly infected. In this case, as expected,
differences at the 10
7 cell dose were not observed due to
the increased susceptibility
of DBA/2 mice to
C. albicans
infections, both strains producing
a high mortality. However,
differences in MST were observed for
the mutant and wild type at a
challenge dose of 10
6 cells (Table
2), and the use of this mouse strain
allowed us
to detect differences between both
C. albicans
strains when a
small inoculum dose (10
5) was used (Table
2). In all these experiments,
ura3 auxotrophic
strains were
avoided due to the effect that this nutritional requirement
(especially
in certain genetic backgrounds) has on
C. albicans virulence
(
29,
69). However, since the
hog1 knockout
strains
were obtained in a
his1 background (RM1000), it was
confirmed
that
HIS1 did not play a role in the observed
reduction in virulence,
as shown for the control strains RM100 and
CNCH1 (Fig.
7A). In
addition, the
hog1 heterozygous strain
CNC15-10 (a strain obtained
through the reintroduction of the
HOG1 gene in the genome of strain
CNC15 [see Materials and
Methods] to serve as an internal control
of the knockout deletion
scheme used) displayed virulence similar
to that of wild-type (SC5314)
cells (Fig.
7A), indicating that
a single copy of the
HOG1
gene is enough to restore full virulence
in this animal model. The
fungal burden was quantified in the
kidney and brain, representative
organs of
C. albicans infections
(
59). Organs
were recovered at different times postinfection,
and viable cells were
quantified. As shown in Table
3, strain
CNC13 colonizes tissues less efficiently than SC5314 does and
it is
cleared from the brains of BALB/c mice in a few days (i.e.,
7 days,
even with the high dose of 10
6 cells). Collectively, these
data indicate that a functional HOG
pathway is essential for the
maintenance of full virulence in
C. albicans.
| |
DISCUSSION |
In this work, we have addressed the role of the HOG pathway
through the characterization of the phenotype of C. albicans
mutants defective in the central MAP kinase gene of this pathway, the HOG1 gene, under both restrictive and permissive conditions.
DNA replication was insensitive (at least for the period analyzed) to
high osmolarity, and the increased DNA content detected by flow
cytometry was the result of a block in cytokinesis, similar to that in
S. cerevisiae mutants (7). We also found that the defects in cell separation are localized to the last stages of cytokinesis but are, apparently, not due to abnormal septum formation (Fig. 3A and B); instead, we show that chitinase activity is low and
may be limiting under these conditions. This is supported not only by
the enzymatic analysis of osmostressed cells but also by the effect
that externally added chitinase (and not other cell wall lytic enzyme
preparations such as zymolyase or glusulase) exerts on cell separation.
Also, certain components of the bud polarity machinery appear to be
nonfunctional in the mutant cells under restrictive conditions, a
phenomenon similar to that of S. cerevisiae, where transfer
of the cells to high-osmolarity conditions often results in the
selection of a new polarization region for bud emergence to occur
(7).
An interesting conclusion from our studies is the suggestion of a link
between cell wall metabolism and the HOG pathway. This is inferred from
the resistance to compounds which interact with the cell wall of the
mutant strain in ways different from those of the wild type. A possible
explanation for this result is that hog1 mutants are altered
in their permeability by certain compounds. In fact, nikkomycin Z is a
nucleoside-peptide antibiotic inhibitor of chitin synthase (8,
19) which is imported into the cell through a peptide transport
system (48, 61, 79). Alterations in membrane permeability
cannot, in principle, be excluded, although these effects are also
obtained with dyes such as calcofluor white or Congo red, which show
affinity for external cell wall polymers. The HOG pathway could,
therefore, play an as-yet-undefined role in cell wall metabolism. Such
a relationship has, in fact, been postulated to occur in S. cerevisiae, since PBS2 (the HOG1 MAP kinase
kinase gene) may regulate -(1,6)-glucan assembly (27, 35). No defects in chitin synthase activity (35) were
observed in this study in pbs2
mutants, in agreement with
our results on quantification of the chitin content in hog1 mutants.
Another aspect of biological relevance that we investigated is
dimorphism, a long-suspected mechanism of virulence (see references 13 and 30). The repressive effect
that this pathway exerts on pseudohyphal formation is evidenced by the
hyperfilamentous phenotype of C. albicans strains on
different media such as SLAD medium (21) (a similar
phenotype has been observed for S. cerevisiae hog1 mutants
[cited in reference 42]) as well as by the
suppression of the pseudodimorphic transition in S. cerevisiae when the C. albicans HOG1 gene is
overexpressed. Alterations in the colony morphology on different solid
media may also support this observation, although the apparently
contradictory results observed could be explained by the involvement of
different signal transduction pathways in these processes. Alterations
in colony morphology are also observed in response to serum, and the
conditions used in this assay (1 to 20% serum versus 100% serum) may
better reflect the complex environmental conditions that a pathogen
finds inside the human body, where different locations may have
different concentrations of an inducer(s). Our results indicate the
repression that the HOG pathway exerts on the serum-induced dimorphic
transition in C. albicans. Given our current knowledge of
signal transduction pathways mediated through MAP kinases, it is
tempting to speculate about the final targets of this cascade. In
C. albicans, hyphal formation seems to be a complex process
in which both positive and negative signals do play a role (see
reference 45 for an elegant model). For example, the
HOG pathway could be involved in the repression of the pathway that
leads to a pseudofilamentous or filamentous growth pathway in C. albicans, interacting with those elements of the mating-hyphal
pathway presumably involved in dimorphic transition. In fact, in
S. cerevisiae, elements of the mating pathway are used for
pseudofilamentous growth (32, 36, 40), and it has been shown
that the HOG pathway represses the activity of the mating pathway in
S. cerevisiae (22). Furthermore, recent studies
in S. cerevisiae (57) reveal that HOG1
prevents cross talking between both the mating and HOG pathways. The
repressive role of the HOG pathway in C. albicans hyphal
formation could be its involvement in the activation of
RBF1, a transcription factor whose deletion generates hyphal
forms (26), or, alternatively, a putative
SSN6-TUP1 complex in C. albicans. In fact, it has
been recently shown that the S. cerevisiae Ssn6-Tup1
repressor complex (28) plays a role in the repression of
different osmolarity-inducible genes in S. cerevisiae (some
of which are HOG1 dependent) and that ssn6 or
tup1 mutants partially suppress the characteristic osmotic
sensitivity associated with hog1 mutants (47).
More interestingly, the C. albicans TUP1 gene has been shown
to play a role in hyphal formation in C. albicans since
deletion of this gene results in a gene dosage-dependent filamentous
growth (5). A possible explanation for our results would be
the HOG1-dependent expression or activation of a DNA binding
protein able to recruit the Ssn6-Tup1 complex for the repression of
specific hyphal genes. In any case, these similarities must be analyzed
carefully because of the pleiotropic role of transcription factors like
TUP1 in fungal cell physiology and the fact that phenotypes
associated with S. cerevisiae and C. albicans
mutants may clearly diverge, as occurs with tup1 mutants
(5).
It is noteworthy that other elements of this pathway have been found to
play a role in hyphal development. For example, deletion of the
nik-1+ gene, a Neurospora crassa
homologue of the SLN1 gene (58), results, in
addition to osmotic sensitivity, in restricted mycelial growth, the
loss of conidiophore development, and in aberrant hyphal structures
under restrictive conditions (1). Recently, two-component
C. albicans kinase gene homologues of SLN1 have been identified (10, 50, 74) and effects on the efficiency of the transition process have been observed (74).
Our results also demonstrate that the HOG pathway plays a major role in
C. albicans virulence. The genes involved in virulence currently identified are functionally diverse, probably reflecting the
character of a commensal opportunistic pathogen instead of a primary
pathogen of C. albicans. Dimorphism provides a morphological switch that has been related to certain features undoubtedly related to
pathogenicity, such as adhesion, escape from phagocytic cells, and
invasion (9, 30, 56, 66). It is therefore not surprising that strains defective in hyphal formation (under certain conditions) should display a reduced virulence, as has been shown for some signal
transduction protein kinases (15, 36, 37). However, although
the role that hyphal formation must play in virulence is evident, our
results clearly demonstrate that this trait is not enough for
virulence, since a functional (and even enhanced) in vitro hyphal
development does not necessarily correlate with virulence in this
animal model, as suggested recently (14). It should be
emphasized that both the dose of cells used in the virulence
experiments and the length of the period in which mice infected were
followed up indicate the complete avirulence of the mutant strain, in
comparison with the standard defined in other recent studies (14,
41), and suggest that the HOG pathway participates in other
as-yet-unraveled cellular processes which are essential for virulence.
Although it is difficult to define what this role is at this stage, it
is tempting to speculate that Hog1p behaves like a general stress
kinase, similar to the S. pombe homologue, and that this
cellular response is essential for the successful establishment of an
infection in the host. In conclusion, we show in this work that the
pathway(s) controlling osmotic sensitivity in C. albicans
also plays a role in differentiation programs and virulence in this
pathogenic fungus, a result which identifies this route of primary
importance in the search for novel antifungal targets.
| |
ACKNOWLEDGMENTS |
We thank Alistair J. P. Brown for generously providing
strain L5366. Calcofluor was a generous gift from Bayer. The excellent assistance of A. Vázquez and A. Álvarez from the Centro de
Citometría de Flujo y Microscopía Confocal of the UCM
and M. J. Asensio Vela is acknowledged. Electron microscopy was
carried out at the Centro de Microscopía Electrónica
"Luis Bru" of the UCM. We also thank M. Molina for critical reading
of the manuscript.
R. Alonso Monge is recipient of a fellowship from the Comunidad
Autónoma de Madrid. This work was supported by FIS grant SAF96-1540 and by grant FISS97/0047-01.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Departamento de
Microbiología II, Facultad de Farmacia, Universidad Complutense
de Madrid, Plaza de Ramón y Cajal s/n, E-28040 Madrid, Spain.
Phone: 34 91 3941617. Fax: 34 91 3941745. E-mail:
jesuspla{at}eucmax.sim.ucm.es.
Present address: Department of Biochemistry & Cell Biology, Rice
University, Houston, TX 77005-1892.
| |
REFERENCES |
| 1.
|
Alex, L. A.,
K. A. Borkovich, and M. I. Simon.
1996.
Hyphal development in Neurospora crassa: involvement of a two-component histidine kinase.
Proc. Natl. Acad. Sci. USA
93:3416-3421[Abstract/Free Full Text].
|
| 2.
|
Ausubel, F. M.,
R. E. Kingston,
R. Brent, et al. (ed.).
1993.
Current protocols in molecular biology.
Wiley Interscience, New York, N.Y.
|
| 3.
|
Banuett, F.
1998.
Signalling in the yeasts: an informational cascade with links to the filamentous fungi.
Microbiol. Mol. Biol. Rev.
62:249-274[Abstract/Free Full Text].
|
| 4.
|
Blomberg, A., and L. Adler.
1992.
Physiology of osmotolerance in fungi.
Adv. Microb. Physiol.
33:145-212[Medline].
|
| 5.
|
Braun, B. R., and A. D. Johnson.
1997.
Control of filament formation in Candida albicans by the transcriptional repressor TUP1.
Science
277:105-109[Abstract/Free Full Text].
|
| 6.
|
Brewster, J. L.,
T. de Valoir,
N. D. Dwyer,
E. Winter, and M. C. Gustin.
1993.
An osmosensing signal transduction pathway in yeast.
Science
259:1760-1763[Abstract/Free Full Text].
|
| 7.
|
Brewster, J. L., and M. C. Gustin.
1994.
Positioning of cell growth and division after osmotic stress requires a MAP kinase pathway.
Yeast
10:425-439[Medline].
|
| 8.
|
Cabib, E.
1991.
Differential inhibition of chitin synthetases 1 and 2 from Saccharomyces cerevisiae by polyoxin D and nikkomycins.
Antimicrob. Agents Chemother.
35:170-173[Abstract/Free Full Text].
|
| 9.
|
Calderone, R. A.
1993.
Recognition between Candida albicans and host cells.
Trends Microbiol.
1:55-58[Medline].
|
| 10.
|
Calera, J. A.,
G. H. Choi, and R. A. Calderone.
1998.
Identification of a putative histidine kinase two-component phosphorelay gene (CaHK1) in Candida albicans.
Yeast
14:665-674[Medline].
|
| 11.
|
Chowdhury, S.,
K. W. Smith, and M. C. Gustin.
1992.
Osmotic stress and the yeast cytoskeleton: phenotype-specific suppression of an actin mutation.
J. Cell Biol.
118:561-571[Abstract/Free Full Text].
|
| 12.
|
Cid, V. J.,
A. Durán,
F. del Rey,
M. P. Snyder,
C. Nombela, and M. Sánchez.
1995.
Molecular basis of cell integrity and morphogenesis in Saccharomyces cerevisiae.
Microbiol. Rev.
59:345-386[Abstract/Free Full Text].
|
| 13.
|
Corner, B. E., and P. T. Magee.
1997.
Candida pathogenesis: unravelling the threads of infection.
Curr. Biol.
7:R691-R694[Medline].
|
| 14.
|
Csank, C.,
C. Makris,
S. Meloche,
K. Schröppel,
M. Röllinghoff,
D. Dignard,
D. Y. Thomas, and M. Whiteway.
1997.
Derepressed hyphal growth and reduced virulence in a VH1 family-related protein phosphatase mutant of the human pathogen Candida albicans.
Mol. Biol. Cell
8:2539-2551[Abstract/Free Full Text].
|
| 15.
|
Csank, C.,
K. Schröppel,
E. Leberer,
D. Harcus,
O. Mohamed,
S. Meloche,
D. Y. Thomas, and M. Whiteway.
1998.
Roles of the Candida albicans mitogen-activated protein kinase homolog, Cek1p, in hyphal development and systemic candidiasis.
Infect. Immun.
66:2713-2721[Abstract/Free Full Text].
|
| 16.
|
de la Fuente, J. M.,
A. Alvarez,
C. Nombela, and M. Sánchez.
1992.
Flow cytometric analysis of Saccharomyces cerevisiae autolytic mutants and protoplasts.
Yeast
8:39-45[Medline].
|
| 17.
|
Díez-Orejas, R.,
G. Molero,
F. Navarro-García,
J. Pla,
C. Nombela, and M. Sánchez-Pérez.
1997.
Reduced virulence of Candida albicans MKC1 mutants: a role for a mitogen-activated protein kinase in pathogenesis.
Infect. Immun.
65:833-837[Abstract].
|
| 18.
|
Fonzi, W. A., and M. Y. Irwin.
1993.
Isogenic strain construction and gene mapping in Candida albicans.
Genetics
134:717-728[Abstract].
|
| 19.
|
Gaughran, J. P.,
M. H. Lai,
D. R. Kirsch, and S. J. Silverman.
1994.
Nikkomycin Z is a specific inhibitor of Saccharomyces cerevisiae chitin synthase isozyme Chs3 in vitro and in vivo.
J. Bacteriol.
176:5857-5860[Abstract/Free Full Text].
|
| 20.
|
Gillum, A. M.,
E. Y. H. Tsay, and D. R. Kirsch.
1984.
Isolation of the Candida albicans gene for orotidine-5'-phosphate decarboxylase by complementation of S. cerevisiae ura3 and E. coli pyrF mutations.
Mol. Gen. Genet.
198:179-182[Medline].
|
| 21.
|
Gimeno, C. J.,
P. O. Ljungdahl,
C. A. Styles, and G. R. Fink.
1992.
Unipolar cell divisions in the yeast S. cerevisiae lead to filamentous growth: regulation by starvation and RAS.
Cell
68:1077-1090[Medline].
|
| 22.
|
Hall, J. P.,
V. Cherkasova,
E. A. Elion,
M. C. Gustin, and E. Winter.
1996.
The osmoregulatory pathway represses mating pathway activity in Saccharomyces cerevisiae: isolation of a FUS3 mutant that is insensitive to the repression mechanism.
Mol. Cell. Biol.
16:6715-6723[Abstract].
|
| 23.
|
Hanahan, D.
1988.
Techniques for transformation of E. coli, p. 109-135.
In
D. M. Glover (ed.), DNA cloning. IRL Press, Oxford, United Kingdom.
|
| 24.
|
Hector, R. F.,
J. E. Domer, and E. W. Carrow.
1982.
Immune responses to Candida albicans in genetically distinct mice.
Infect. Immun.
38:1020-1028[Abstract/Free Full Text].
|
| 25.
|
Hill, J. E.,
A. M. Myers,
T. J. Koerner, and A. Tzagoloff.
1986.
Yeast/E. coli shuttle vectors with multiple unique restriction sites.
Yeast
2:163-167[Medline].
|
| 26.
|
Ishii, N.,
M. Yamamoto,
F. Yoshihara,
M. Arisawa, and Y. Aoki.
1997.
Biochemical and genetic characterization of Rbf1p, a putative transcription factor of Candida albicans.
Microbiology
143:429-435[Abstract/Free Full Text].
|
| 27.
|
Jiang, B.,
A. F. J. Ram,
J. Sheraton,
F. M. Klis, and H. Bussey.
1995.
Regulation of cell wall beta-glucan assembly: PTC1 negatively affects PBS2 action in a pathway that includes modulation of EXG1 transcription.
Mol. Gen. Genet.
248:260-269[Medline].
|
| 28.
|
Keleher, C. A.,
M. J. Redd,
J. Schultz,
M. Carlson, and A. D. Johnson.
1992.
Ssn6-Tup1 is a general repressor of transcription in yeast.
Cell
68:709-719[Medline].
|
| 29.
|
Kirsch, D. R., and R. R. Whitney.
1991.
Pathogenicity of Candida albicans auxotrophic mutants in experimental infections.
Infect. Immun.
59:3297-3300[Abstract/Free Full Text].
|
| 30.
|
Kobayashi, G. S., and J. E. Cutler.
1998.
Candida albicans hyphal formation and virulence: is there a clearly defined role?
Trends Microbiol.
6:92-94[Medline].
|
| 31.
|
Köhler, G. A.,
T. C. White, and N. Agabian.
1997.
Overexpression of a cloned IMP dehydrogenase gene of Candida albicans confers resistance to the specific inhibitor mycophenolic acid.
J. Bacteriol.
179:2331-2338[Abstract/Free Full Text].
|
| 32.
|
Köhler, J., and G. R. Fink.
1996.
Candida albicans strains heterozygous and homozygous for mutations in mitogen-activated protein kinase signaling components have defects in hyphal development.
Proc. Natl. Acad. Sci. USA
93:13223-13228[Abstract/Free Full Text].
|
| 33.
|
Kron, S. J.,
C. A. Styles, and G. R. Fink.
1994.
Symmetric cell division in pseudohyphae of the yeast Saccharomyces cerevisiae.
Mol. Biol. Cell
5:1003-1022[Abstract].
|
| 34.
|
Kuranda, M. J., and P. W. Robbins.
1991.
Chitinase is required for cell separation during growth of Saccharomyces cerevisiae.
J. Biol. Chem.
266:19758-19767[Abstract/Free Full Text].
|
| 35.
|
Lai, M. H.,
S. J. Silverman,
J. P. Gaughran, and D. R. Kirsch.
1997.
Multiple copies of PBS2, MHP1 or LRE1 produce glucanase resistance and other cell wall effects in Saccharomyces cerevisiae.
Yeast
13:199-213[Medline].
|
| 36.
|
Leberer, E.,
D. Harcus,
I. D. Broadbent,
K. L. Clark,
D. Dignard,
K. Ziegelbauer,
A. Schmidt,
N. A. R. Gow,
A. J. P. Brown, and D. Y. Thomas.
1996.
Signal transduction through homologs of the Ste20p and Ste7p protein kinases can trigger hyphal formation in the pathogenic fungus Candida albicans.
Proc. Natl. Acad. Sci. USA
93:13217-13222[Abstract/Free Full Text].
|
| 37.
|
Leberer, E.,
K. Ziegelbauer,
A. Schmidt,
D. Harcus,
D. Dignard,
J. Ash,
L. Johnson, and D. Y. Thomas.
1997.
Virulence and hyphal formation of Candida albicans require the Ste20p-like protein kinase CaCla4p.
Curr. Biol.
7:539-546[Medline].
|
| 38.
|
Lee, K. L.,
H. R. Buckley, and C. C. Campbell.
1975.
An amino acid liquid synthetic medium for the development of mycelial and yeast forms of Candida albicans.
J. Med. Vet. Mycol.
13:148-153.
|
| 39.
|
Liu, H.,
J. Köhler, and G. R. Fink.
1994.
Suppression of hyphal formation in Candida albicans by mutation of a STE12 homolog.
Science
266:1723-1726[Abstract/Free Full Text].
|
| 40.
|
Liu, H.,
C. A. Styles, and G. R. Fink.
1993.
Elements of the yeast pheromone response pathway required for filamentous growth of diploids.
Science
262:1741-1744[Abstract/Free Full Text].
|
| 41.
|
Lo, H. J.,
J. R. Kohler,
B. DiDomenico,
D. Loebenberg,
A. Cacciapuoti, and G. R. Fink.
1997.
Nonfilamentous C. albicans mutants are avirulent.
Cell
90:939-949[Medline].
|
| 42.
|
Madhani, H. D.,
C. A. Styles, and G. R. Fink.
1997.
MAP kinases with distinct inhibitory functions impart signaling specificity during yeast differentiation.
Cell
91:673-684[Medline].
|
| 43.
|
Maeda, T.,
M. Takekawa, and H. Saito.
1995.
Activation of yeast PBS2 MAPKK by MAPKKKs or by binding of an SH3-containing osmosensor.
Science
269:554-558X[Abstract/Free Full Text].
|
| 44.
|
Maeda, T.,
S. M. Wurgler-Murphy, and H. Saito.
1994.
A two-component system that regulates an osmosensing MAP kinase cascade in yeast.
Nature
369:242-245[Medline].
|
| 45.
|
Magee, P. T.
1998.
Which came first: the hypha or the yeast?
Science
277:52-53[Free Full Text].
|
| 46.
|
Malathi, K.,
K. Ganesan, and A. Datta.
1994.
Identification of a putative transcription factor in Candida albicans that can complement the mating defect of Saccharomyces cerevisiae ste12 mutants.
J. Biol. Chem.
269:22945-22951[Abstract/Free Full Text].
|
| 47.
|
Márquez, J. A.,
A. Pascual-Ahuir,
M. Proft, and R. Serrano.
1998.
The Ssn6-Tup1 repressor complex of Saccharomyces cerevisiae is involved in the osmotic induction of HOG-dependent and -independent genes.
EMBO J.
17:2543-2553[Medline].
|
| 48.
|
McCarthy, P. J.,
P. F. Troke, and K. Gull.
1985.
Mechanism of action of nikkomycin and the peptide transport system of Candida albicans.
J. Gen. Microbiol.
131:775-780[Abstract/Free Full Text].
|
| 49.
|
Miret, J. J.,
A. J. Solari,
P. A. Barderi, and S. H. Goldemberg.
1992.
Polyamines and cell wall organization in Saccharomyces cerevisiae.
Yeast
8:1033-1041[Medline].
|
| 50.
|
Nagahashi, S.,
T. Mio,
N. Ono,
T. Yamada-Okabe,
M. Arisawa,
H. Bussey, and H. Yamada-Okabe.
1998.
Isolation of CaSLN1 and CaNIK1, the genes for osmosensing histidine kinase homologues, from the pathogenic fungus Candida albicans.
Microbiology
144:425-432[Abstract/Free Full Text].
|
| 51.
|
National Committee for Clinical Laboratory Standards.
1992.
Reference method for broth dilution antifungal susceptibility testing of yeast. Proposed standard M27-P.
National Committee for Clinical Laboratory Standards, Villanova, Pa.
|
| 52.
|
Navarro-García, F.,
R. Alonso-Monge,
H. Rico,
J. Pla,
R. Sentandreu, and C. Nombela.
1998.
A role for the MAP kinase gene MKC1 in cell wall construction and morphological transitions in Candida albicans.
Microbiology
144:411-424[Abstract/Free Full Text].
|
| 53.
|
Navarro-García, F.,
M. Sánchez,
J. Pla, and C. Nombela.
1995.
Functional characterization of the MKC1 gene of Candida albicans, which encodes a mitogen-activated protein kinase homolog related to cell integrity.
Mol. Cell. Biol.
15:2197-2206[Abstract].
|
| 54.
|
Negredo, A.,
L. Monteoliva,
C. Gil,
J. Pla, and C. Nombela.
1997.
Cloning, analysis and one-step disruption of the ARG5,6 gene of Candida albicans.
Microbiology
143:297-302[Abstract/Free Full Text].
|
| 55.
|
Odds, F. C.
1988.
Candida and candidosis.
Bailliére Tindall, London, United Kingdom.
|
| 56.
|
Odds, F. C.
1994.
Candida species and virulence.
ASM News
60:313-318.
|
| 57.
|
O'Rourke, S. M., and I. Herskowitz.
1998.
The Hog1 MAPK prevents cross talk between the HOG and pheromone response MAPK pathways in Saccharomyces cerevisiae.
Genes Dev.
12:2874-2886[Abstract/Free Full Text].
|
| 58.
|
Ota, I. M., and A. Varshavsky.
1993.
A yeast protein similar to bacterial two-component regulators.
Science
262:566-569[Abstract/Free Full Text].
|
| 59.
|
Papadimitriou, J. M., and R. B. Ashman.
1986.
The pathogenesis of acute systemic candidiasis in a susceptible inbred mouse strain.
J. Pathol.
150:257-265[Medline].
|
| 60.
|
Paravicini, G.,
A. Mendoza,
B. Antonsson,
M. Cooper,
C. Losberger, and M. Payton.
1996.
The Candida albicans PKC1 gene encodes a protein kinase C homolog necessary for cellular integrity but not dimorphism.
Yeast
12:741-756[Medline].
|
| 61.
|
Payne, J. W., and D. A. Shallow.
1985.
Studies on drug targetting in the pathogenic fungus C. albicans: peptide transport mutants resistant to polyoxins, nikkomycins and bacilysin.
FEMS Microbiol. Lett.
28:55-60.
|
| 62.
|
Pla, J.,
C. Gil,
L. Monteoliva,
F. Navarro-García,
M. Sánchez, and C. Nombela.
1996.
Understanding Candida albicans at the molecular level.
Yeast
12:1677-1702[Medline].
|
| 63.
|
Pla, J.,
R. M. Pérez-Díaz,
F. Navarro-García,
M. Sánchez, and C. Nombela.
1995.
Cloning of the Candida albicans HIS1 gene by direct complementation of a C. albicans histidine auxotroph using an improved double-ARS shuttle vector.
Gene
165:115-120[Medline].
|
| 64.
|
Posas, F., and H. Saito.
1997.
Osmotic activation of the HOG MAPK pathway via Ste11p MAPKKK: scaffold role of Pbs2p MAPKK.
Science
276:1702-1705[Abstract/Free Full Text].
|
| 65.
|
Posas, F.,
S. M. Wurgler-Murphy,
T. Maeda,
E. A. Witten,
T. C. Thai, and H. Saito.
1996.
Yeast HOG1 MAP kinase cascade is regulated by a multistep phosphorelay mechanism in the SLN1-YPD1-SSK1 "two-component" osmosensor.
Cell
86:865-875[Medline].
|
| 66.
|
Ryley, J. F., and N. G. Ryley.
1990.
Candida albicans do mycelia matter?
J. Med. Vet. Mycol.
28:225-239[Medline].
|
| 67.
|
San José, C.,
R. Alonso,
R. M. Pérez-Díaz,
J. Pla, and C. Nombela.
1996.
The mitogen-activated protein kinase homolog HOG1 gene controls glycerol accumulation in the pathogenic fungus Candida albicans.
J. Bacteriol.
178:5850-5852[Abstract/Free Full Text].
|
| 68.
|
Scherer, S., and P. T. Magee.
1990.
Genetics of Candida albicans.
Microbiol. Rev.
54:226-241[Abstract/Free Full Text].
|
| 69.
|
Shepherd, M. G.
1985.
Pathogenicity of morphological and auxotrophic mutants of Candida albicans in experimental infections.
Infect. Immun.
50:541-544[Abstract/Free Full Text].
|
| 70.
|
Shiozaki, K., and P. Russell.
1995.
Cell-cycle control linked to extracellular environment by MAP kinase pathway in fission yeast.
Nature
378:739-743[Medline].
|
| 71.
|
Shiozaki, K., and P. Russell.
1996.
Conjugation, meiosis, and the osmotic stress response are regulated by Spc1 kinase through Atf1 transcription factor in fission yeast.
Genes Dev.
10:2276-2288[Abstract/Free Full Text].
|
| 72.
|
Singh, P.,
K. Ganesan,
K. Malathi,
D. Ghosh, and A. Datta.
1994.
ACPR, a STE12 homologue from Candida albicans, is a strong inducer of pseudohyphae in Saccharomyces cerevisiae haploids and diploids.
Biochem. Biophys. Res. Commun.
205:1079-1085[Medline].
|
| 73.
|
Singh, P.,
S. Ghosh, and A. Datta.
1997.
A novel MAP-kinase kinase from Candida albicans.
Gene
190:99-104[Medline].
|
| 74.
|
Srikantha, T.,
L. Tsai,
K. Daniels,
L. Enger,
K. Highley, and D. R. Soll.
1998.
The two-component hybrid kinase regulator caNIK1 of Candida albicans.
Microbiology
144:2715-2729[Abstract/Free Full Text].
|
| 75.
|
Tiedt, L. R.,
W. R. Jooste, and V. L. Hamilton-Attwell.
1987.
Technique for preserving aerial fungus structure for scanning electron microscopy.
Trans. Br. Mycol.
88:420-422.
|
| 76.
|
Tsang, T.,
V. Copeland, and G. T. Bowden.
1991.
A set of cassette cloning vectors for rapid and versatile adaptation of restriction fragments.
Biotechniques
10:330[Medline].
|
| 77.
|
Whiteway, M.,
D. Dignard, and D. Y. Thomas.
1992.
Dominant negative selection of heterologous genes: isolation of Candida albicans genes that interfere with Saccharomyces cerevisiae mating factor-induced cell cycle arrest.
Proc. Natl. Acad. Sci. USA
89:9410-9414[Abstract/Free Full Text].
|
| 78.
|
Williams, S., and C. Veldkamp.
1974.
Preparation of fungi for scanning electron microscopy.
Trans. Br. Mycol.
63:409-412.
|
| 79.
|
Yadan, J. C.,
M. Gonneau,
P. Sarthou, and F. Le Goffic.
1984.
Sensitivity to nikkomycin Z in Candida albicans: role of peptide permeases.
J. Bacteriol.
160:884-888[Abstract/Free Full Text].
|
Journal of Bacteriology, May 1999, p. 3058-3068, Vol. 181, No. 10
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
This article has been cited by other articles:
-
Rodaki, A., Bohovych, I. M., Enjalbert, B., Young, T., Odds, F. C., Gow, N. A.R., Brown, A. J.P.
(2009). Glucose Promotes Stress Resistance in the Fungal Pathogen Candida albicans. Mol. Biol. Cell
20: 4845-4855
[Abstract]
[Full Text]
-
Bamford, C. V., d'Mello, A., Nobbs, A. H., Dutton, L. C., Vickerman, M. M., Jenkinson, H. F.
(2009). Streptococcus gordonii Modulates Candida albicans Biofilm Formation through Intergeneric Communication. Infect. Immun.
77: 3696-3704
[Abstract]
[Full Text]
-
Roman, E., Cottier, F., Ernst, J. F., Pla, J.
(2009). Msb2 Signaling Mucin Controls Activation of Cek1 Mitogen-Activated Protein Kinase in Candida albicans. Eukaryot Cell
8: 1235-1249
[Abstract]
[Full Text]
-
Ko, Y.-J., Yu, Y. M., Kim, G.-B., Lee, G.-W., Maeng, P. J., Kim, S., Floyd, A., Heitman, J., Bahn, Y.-S.
(2009). Remodeling of Global Transcription Patterns of Cryptococcus neoformans Genes Mediated by the Stress-Activated HOG Signaling Pathways. Eukaryot Cell
8: 1197-1217
[Abstract]
[Full Text]
-
Kayingo, G., Martins, A., Andrie, R., Neves, L., Lucas, C., Wong, B.
(2009). A permease encoded by STL1 is required for active glycerol uptake by Candida albicans. Microbiology
155: 1547-1557
[Abstract]
[Full Text]
-
Alonso-Monge, R., Carvaihlo, S., Nombela, C., Rial, E., Pla, J.
(2009). The Hog1 MAP kinase controls respiratory metabolism in the fungal pathogen Candida albicans. Microbiology
155: 413-423
[Abstract]
[Full Text]
-
Bahn, Y.-S.
(2008). Master and Commander in Fungal Pathogens: the Two-Component System and the HOG Signaling Pathway. Eukaryot Cell
7: 2017-2036
[Full Text]
-
Ramsdale, M., Selway, L., Stead, D., Walker, J., Yin, Z., Nicholls, S. M., Crowe, J., Sheils, E. M., Brown, A. J.P.
(2008). MNL1 Regulates Weak Acid-induced Stress Responses of the Fungal Pathogen Candida albicans. Mol. Biol. Cell
19: 4393-4403
[Abstract]
[Full Text]
-
Legrand, M., Chan, C. L., Jauert, P. A., Kirkpatrick, D. T.
(2008). Analysis of base excision and nucleotide excision repair in Candida albicans. Microbiology
154: 2446-2456
[Abstract]
[Full Text]
-
Lin, X., Nielsen, K., Patel, S., Heitman, J.
(2008). Impact of Mating Type, Serotype, and Ploidy on the Virulence of Cryptococcus neoformans. Infect. Immun.
76: 2923-2938
[Abstract]
[Full Text]
-
Yi, S., Sahni, N., Daniels, K. J., Pujol, C., Srikantha, T., Soll, D. R.
(2008). The Same Receptor, G Protein, and Mitogen-activated Protein Kinase Pathway Activate Different Downstream Regulators in the Alternative White and Opaque Pheromone Responses of Candida albicans. Mol. Biol. Cell
19: 957-970
[Abstract]
[Full Text]
-
Bahn, Y.-S., Geunes-Boyer, S., Heitman, J.
(2007). Ssk2 Mitogen-Activated Protein Kinase Kinase Kinase Governs Divergent Patterns of the Stress-Activated Hog1 Signaling Pathway in Cryptococcus neoformans. Eukaryot Cell
6: 2278-2289
[Abstract]
[Full Text]
-
Cheetham, J., Smith, D. A., da Silva Dantas, A., Doris, K. S., Patterson, M. J., Bruce, C. R., Quinn, J.
(2007). A Single MAPKKK Regulates the Hog1 MAPK Pathway in the Pathogenic Fungus Candida albicans. Mol. Biol. Cell
18: 4603-4614
[Abstract]
[Full Text]
-
Vylkova, S., Jang, W. S., Li, W., Nayyar, N., Edgerton, M.
(2007). Histatin 5 Initiates Osmotic Stress Response in Candida albicans via Activation of the Hog1 Mitogen-Activated Protein Kinase Pathway. Eukaryot Cell
6: 1876-1888
[Abstract]
[Full Text]
-
Gregori, C., Schuller, C., Roetzer, A., Schwarzmuller, T., Ammerer, G., Kuchler, K.
(2007). The High-Osmolarity Glycerol Response Pathway in the Human Fungal Pathogen Candida glabrata Strain ATCC 2001 Lacks a Signaling Branch That Operates in Baker's Yeast. Eukaryot Cell
6: 1635-1645
[Abstract]
[Full Text]
-
Biswas, S., Van Dijck, P., Datta, A.
(2007). Environmental Sensing and Signal Transduction Pathways Regulating Morphopathogenic Determinants of Candida albicans. Microbiol. Mol. Biol. Rev.
71: 348-376
[Abstract]
[Full Text]
-
Enjalbert, B., MacCallum, D. M., Odds, F. C., Brown, A. J. P.
(2007). Niche-Specific Activation of the Oxidative Stress Response by the Pathogenic Fungus Candida albicans. Infect. Immun.
75: 2143-2151
[Abstract]
[Full Text]
-
Hernandez-Lopez, M. J., Randez-Gil, F., Prieto, J. A.
(2006). Hog1 Mitogen-Activated Protein Kinase Plays Conserved and Distinct Roles in the Osmotolerant Yeast Torulaspora delbrueckii.. Eukaryot Cell
5: 1410-1419
[Abstract]
[Full Text]
-
Bahn, Y.-S., Kojima, K., Cox, G. M., Heitman, J.
(2006). A Unique Fungal Two-Component System Regulates Stress Responses, Drug Sensitivity, Sexual Development, and Virulence of Cryptococcus neoformans. Mol. Biol. Cell
17: 3122-3135
[Abstract]
[Full Text]
-
Monge, R. A., Roman, E., Nombela, C., Pla, J.
(2006). The MAP kinase signal transduction network in Candida albicans.. Microbiology
152: 905-912
[Abstract]
[Full Text]
-
Hernandez-Lopez, M. J., Panadero, J., Prieto, J. A., Randez-Gil, F.
(2006). Regulation of Salt Tolerance by Torulaspora delbrueckii Calcineurin Target Crz1p. Eukaryot Cell
5: 469-479
[Abstract]
[Full Text]
-
Eisman, B., Alonso-Monge, R., Roman, E., Arana, D., Nombela, C., Pla, J.
(2006). The Cek1 and Hog1 Mitogen-Activated Protein Kinases Play Complementary Roles in Cell Wall Biogenesis and Chlamydospore Formation in the Fungal Pathogen Candida albicans. Eukaryot Cell
5: 347-358
[Abstract]
[Full Text]
-
Enjalbert, B., Smith, D. A., Cornell, M. J., Alam, I., Nicholls, S., Brown, A. J.P., Quinn, J.
(2006). Role of the Hog1 Stress-activated Protein Kinase in the Global Transcriptional Response to Stress in the Fungal Pathogen Candida albicans. Mol. Biol. Cell
17: 1018-1032
[Abstract]
[Full Text]
-
Roman, E., Nombela, C., Pla, J.
(2005). The Sho1 Adaptor Protein Links Oxidative Stress to Morphogenesis and Cell Wall Biosynthesis in the Fungal Pathogen Candida albicans. Mol. Cell. Biol.
25: 10611-10627
[Abstract]
[Full Text]
-
Kayingo, G., Wong, B.
(2005). The MAP kinase Hog1p differentially regulates stress-induced production and accumulation of glycerol and D-arabitol in Candida albicans. Microbiology
151: 2987-2999
[Abstract]
[Full Text]
-
Prasad, T., Saini, P., Gaur, N. A., Vishwakarma, R. A., Khan, L. A., Haq, Q. M. R., Prasad, R.
(2005). Functional Analysis of CaIPT1, a Sphingolipid Biosynthetic Gene Involved in Multidrug Resistance and Morphogenesis of Candida albicans. Antimicrob. Agents Chemother.
49: 3442-3452
[Abstract]
[Full Text]
-
Navarro-Garcia, F., Eisman, B., Fiuza, S. M., Nombela, C., Pla, J.
(2005). The MAP kinase Mkc1p is activated under different stress conditions in Candida albicans. Microbiology
151: 2737-2749
[Abstract]
[Full Text]
-
Arana, D. M., Nombela, C., Alonso-Monge, R., Pla, J.
(2005). The Pbs2 MAP kinase kinase is essential for the oxidative-stress response in the fungal pathogen Candida albicans. Microbiology
151: 1033-1049
[Abstract]
[Full Text]
-
Ferreira, C., van Voorst, F., Martins, A., Neves, L., Oliveira, R., Kielland-Brandt, M. C., Lucas, C., Brandt, A.
(2005). A Member of the Sugar Transporter Family, Stl1p Is the Glycerol/H+ Symporter in Saccharomyces cerevisiae. Mol. Biol. Cell
16: 2068-2076
[Abstract]
[Full Text]
-
Imai, K., Noda, Y., Adachi, H., Yoda, K.
(2005). A Novel Endoplasmic Reticulum Membrane Protein Rcr1 Regulates Chitin Deposition in the Cell Wall of Saccharomyces cerevisiae. J. Biol. Chem.
280: 8275-8284
[Abstract]
[Full Text]
-
Noble, S. M., Johnson, A. D.
(2005). Strains and Strategies for Large-Scale Gene Deletion Studies of the Diploid Human Fungal Pathogen Candida albicans. Eukaryot Cell
4: 298-309
[Abstract]
[Full Text]
-
Li, D., Gurkovska, V., Sheridan, M., Calderone, R., Chauhan, N.
(2004). Studies on the regulation of the two-component histidine kinase gene CHK1 in Candida albicans using the heterologous lacZ reporter gene. Microbiology
150: 3305-3313
[Abstract]
[Full Text]
-
Hobson, R. P., Munro, C. A., Bates, S., MacCallum, D. M., Cutler, J. E., Heinsbroek, S. E. M., Brown, G. D., Odds, F. C., Gow, N. A.R.
(2004). Loss of Cell Wall Mannosylphosphate in Candida albicans Does Not Influence Macrophage Recognition. J. Biol. Chem.
279: 39628-39635
[Abstract]
[Full Text]
-
Smith, D. A., Nicholls, S., Morgan, B. A., Brown, A. J.P., Quinn, J.
(2004). A Conserved Stress-activated Protein Kinase Regulates a Core Stress Response in the Human Pathogen Candida albicans. Mol. Biol. Cell
15: 4179-4190
[Abstract]
[Full Text]
-
Brand, A., MacCallum, D. M., Brown, A. J. P., Gow, N. A. R., Odds, F. C.
(2004). Ectopic Expression of URA3 Can Influence the Virulence Phenotypes and Proteome of Candida albicans but Can Be Overcome by Targeted Reintegration of URA3 at the RPS10 Locus. Eukaryot Cell
3: 900-909
[Abstract]
[Full Text]
-
Mizutani, O., Nojima, A., Yamamoto, M., Furukawa, K., Fujioka, T., Yamagata, Y., Abe, K., Nakajima, T.
(2004). Disordered Cell Integrity Signaling Caused by Disruption of the kexB Gene in Aspergillus oryzae. Eukaryot Cell
3: 1036-1048
[Abstract]
[Full Text]
-
Ullmann, B. D., Myers, H., Chiranand, W., Lazzell, A. L., Zhao, Q., Vega, L. A., Lopez-Ribot, J. L., Gardner, P. R., Gustin, M. C.
(2004). Inducible Defense Mechanism against Nitric Oxide in Candida albicans. Eukaryot Cell
3: 715-723
[Abstract]
[Full Text]
-
Nobile, C. J., Bruno, V. M., Richard, M. L., Davis, D. A., Mitchell, A. P.
(2003). Genetic control of chlamydospore formation in Candida albicans. Microbiology
149: 3629-3637
[Abstract]
[Full Text]
-
Chauhan, N., Inglis, D., Roman, E., Pla, J., Li, D., Calera, J. A., Calderone, R.
(2003). Candida albicans Response Regulator Gene SSK1 Regulates a Subset of Genes Whose Functions Are Associated with Cell Wall Biosynthesis and Adaptation to Oxidative Stress. Eukaryot Cell
2: 1018-1024
[Abstract]
[Full Text]
-
Wojda, I., Alonso-Monge, R., Bebelman, J.-P., Mager, W. H., Siderius, M.
(2003). Response to high osmotic conditions and elevated temperature in Saccharomyces cerevisiae is controlled by intracellular glycerol and involves coordinate activity of MAP kinase pathways. Microbiology
149: 1193-1204
[Abstract]
[Full Text]
-
Alonso-Monge, R., Navarro-Garcia, F., Roman, E., Negredo, A. I., Eisman, B., Nombela, C., Pla, J.
(2003). The Hog1 Mitogen-Activated Protein Kinase Is Essential in the Oxidative Stress Response and Chlamydospore Formation in Candidaalbicans. Eukaryot Cell
2: 351-361
[Abstract]
[Full Text]
-
Hohmann, S.
(2002). Osmotic Stress Signaling and Osmoadaptation in Yeasts. Microbiol. Mol. Biol. Rev.
66: 300-372
[Abstract]
[Full Text]
-
Van Dijck, P., De Rop, L., Szlufcik, K., Van Ael, E., Thevelein, J. M.
(2002). Disruption of the Candida albicans TPS2 Gene Encoding Trehalose-6-Phosphate Phosphatase Decreases Infectivity without Affecting Hypha Formation. Infect. Immun.
70: 1772-1782
[Abstract]
[Full Text]
-
Zhang, Y., Lamm, R., Pillonel, C., Lam, S., Xu, J.-R.
(2002). Osmoregulation and Fungicide Resistance: the Neurospora crassa os-2 Gene Encodes a HOG1 Mitogen-Activated Protein Kinase Homologue. Appl. Environ. Microbiol.
68: 532-538
[Abstract]
[Full Text]
-
Singh, P., Ghosh, S., Datta, A.
(2001). Attenuation of Virulence and Changes in Morphology in Candida albicans by Disruption of the N-Acetylglucosamine Catabolic Pathway. Infect. Immun.
69: 7898-7903
[Abstract]
[Full Text]
-
Goldstein, A. L., McCusker, J. H.
(2001). Development of Saccharomyces cerevisiae as a Model Pathogen: A System for the Genetic Identification of Gene Products Required for Survival in the Mammalian Host Environment. Genetics
159: 499-513
[Abstract]
[Full Text]
-
Santos, J. L., Shiozaki, K.
(2001). Fungal Histidine Kinases. Sci Signal
2001: re1-re1
[Abstract]
[Full Text]
-
Jong, A. Y., Stins, M. F., Huang, S.-H., Chen, S. H. M., Kim, K. S.
(2001). Traversal of Candida albicans across Human Blood-Brain Barrier In Vitro. Infect. Immun.
69: 4536-4544
[Abstract]
[Full Text]
-
Richard, M., Quijano, R. R., Bezzate, S., Bordon-Pallier, F., Gaillardin, C.
(2001). Tagging Morphogenetic Genes by Insertional Mutagenesis in the Yeast Yarrowia lipolytica. J. Bacteriol.
183: 3098-3107
[Abstract]
[Full Text]
-
Chen, J., Zhou, S., Wang, Q., Chen, X., Pan, T., Liu, H.
(2000). Crk1, a Novel Cdc2-Related Protein Kinase, Is Required for Hyphal Development and Virulence in Candida albicans. Mol. Cell. Biol.
20: 8696-8708
[Abstract]
[Full Text]
-
Bruckmann, A., Künkel, W., Härtl, A., Wetzker, R., Eck, R.
(2000). A phosphatidylinositol 3-kinase of Candida albicans influences adhesion, filamentous growth and virulence. Microbiology
146: 2755-2764
[Abstract]
[Full Text]
-
Ernst, J. F.
(2000). Transcription factors in Candida albicans - environmental control of morphogenesis. Microbiology
146: 1763-1774
[Full Text]
-
Odds, F. C., Van Nuffel, L., Gow, N. A. R.
(2000). Survival in experimental Candida albicans infections depends on inoculum growth conditions as well as animal host. Microbiology
146: 1881-1889
[Abstract]
[Full Text]
-
Calera, J. A., Zhao, X.-J., Calderone, R.
(2000). Defective Hyphal Development and Avirulence Caused by a Deletion of the SSK1 Response Regulator Gene in Candida albicans. Infect. Immun.
68: 518-525
[Abstract]
[Full Text]
-
Thomason, P, Kay, R
(2000). Eukaryotic signal transduction via histidine-aspartate phosphorelay. J. Cell Sci.
113: 3141-3150
[Abstract]
-
Calera, J. A., Zhao, X.-J., De Bernardis, F., Sheridan, M., Calderone, R.
(1999). Avirulence of Candida albicans CaHK1 Mutants in a Murine Model of Hematogenously Disseminated Candidiasis. Infect. Immun.
67: 4280-4284
[Abstract]
[Full Text]
Top
Abstract
Introduction
