Identification and Investigation of Dfi1p signaling intermediates and transcriptional targets in Candida albicans
Abstract: The common
human commensal, Candida albicans, is a polymorphic fungus and a medically significant
opportunistic pathogen. C albicans can undergo a morphological shift between a yeast
form and a hyphal form in response to many environmental stimuli, including growth in
contact with an agar matrix. Wildtype levels of filamentation in response to growth in
contact with an agar matrix ... read morerequire the integral membrane protein, Dfi1p, which
transmits a signal to the mitogen activated protein kinase (MAPK) Cek1p. The first goal
of this work was to identify proteins that participate in signaling to Cek1p during
growth in contact with an agar matrix. Activation of Cek1p required proteins predicted
to participate in the classical Cek1p MAPK cascade, as well as the GTPase Rac1p and its
accessory proteins Dck1p and Lmo1p. Constitutive activation of Rac1p bypassed the Cek1p
activation defect of a dfi1 null strain, demonstrating that Rac1p is epistatic to Dfi1p.
The second goal of this work was to identify transcriptional targets of Dfi1p-dependent
Cek1p activation. For this portion we relied upon ionophore activation of Cek1p in a
Dfi1p-dependent manner during liquid growth. Transcriptional targets of Dfi1p-dependent
Cek1p activation include some members of the Sef1p regulon, which responds to iron
starvation. Three genes of interest were chosen for further study: BMT9, SOD4, and OPT1.
Dfi1p is not required for the transcriptional response to low iron, but is important for
the response to ionophore. BMT9 and OPT1 require Dfi1p for a full transcriptional
response during plated growth. SOD4, however, required Sef1p and not Dfi1p during the
same conditions. OPT1 and SOD4 both responded to activation of another transcription
factor, Czf1p, which is known for promoting embedded filamentation. We propose that the
Dfi1p-dependent transcriptional changes we observed rely on both Sef1p and Czf1p working
simultaneously. The connection between iron starvation and embedded growth is a novel
and intriguing finding.
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Molecular Microbiology.
Advisor: Carol Kumamoto.
Committee: Michael Malamy, Joan Mecsas, and Andrew Camilli.
Keyword: Microbiology.read less