Regulation of Mat Responses by a Differentiation MAPK Pathway in Saccharomyces cerevisiae

Abstract

Fungal species exhibit diverse behaviors when presented with extracellular challenges. Pathogenic fungi can undergo cell differentiation and biofilm formation in response to fluctuating nutrient levels, and these responses are required for virulence. In the model fungal eukaryote Saccharomyces cerevisiae , nutrient limitation induces filamentous growth and biofilm/mat formation. Both responses require the same signal transduction (MAPK) pathway and the same cell adhesion molecule (Flo11) but have been studied under different conditions. We found that filamentous growth and mat formation are aspects of a related response that is regulated by the MAPK pathway. Cells in yeast-form mats differentiated into pseudohyphae in response to nutrient limitation. The MAPK pathway regulated mat expansion (in the plane of the XY-axis) and substrate invasion (downward in the plane of the Z-axis), which optimized the mat's response to extracellular nutrient levels. The MAPK pathway also regulated an upward growth pattern (in the plane of the Z-axis) in response to nutrient limitation and changes in surface rigidity. Upward growth allowed for another level of mat responsiveness and resembled a type of colonial chemorepulsion. Together our results show that signaling pathways play critical roles in regulating social behaviors in which fungal cells participate. Signaling pathways may regulate similar processes in pathogens, whose highly nuanced responses are required for virulence.

Cdc42p-Interacting Protein Bem4p Regulates the Filamentous-Growth Mitogen-Activated Protein Kinase Pathway

“…A PCR fragment containing 600 bp of the CDC24 promoter was amplified with 5= BamHI and 3= PstI sites and introduced into YEp351. A second fragment was generated by PCR that introduced a myristoylation site (55,163) into the N terminus of Cdc24p. This PCR fragment was generated by amplification of CDC24-GFP from strain PC1205.…”

“…Biofilm/mat assays were performed as described previously (70). Colony perimeters were examined for filamentous mats as described previously (55). Mats and colonies were photographed using an Evolution MP Color camera (32-0041C-212; MediaCybernetics, Bethesda, MD).…”

“…Bem4p was required for the development of filamentous mats (Fig. 1H), which occurs under nutrient-limiting conditions (55). Therefore, Bem4p regulates filamentous growth and biofilm/mat formation in haploid and diploid cells.…”

The Filamentous Growth MAPK Pathway Responds to Glucose Starvation Through the Mig1/2 Transcriptional Repressors in Saccharomyces cerevisiae

“…Biofilm and mat assays were carried out on YEP or YEPD plates containing 0.3 or 4% agar (Reynolds and Fink 2001). Mat perimeters were screened by microscopy as described (Karunanithi et al 2012). b-Galactosidase assays were performed as described .…”

“…Like other pathway regulators, Opy2 was required for mat formation on low-agar ( Figure 1C, YEPD 0.3% agar) and high-agar media ( Figure 1C, YEPD 4% agar; Supporting Information, Figure S1). Opy2 was required for cell differentiation into pseudohyphae at mat perimeters, which contain densely aggregated pseudohyphal cells ( Figure 1C, YEP 0.3% agar) (Karunanithi et al 2012). Flo11 is the major adhesion molecule that regulates biofilm/mat formation (Reynolds and Fink 2001;Karunanithi et al 2010) and filamentous/ invasive growth (Lambrechts et al 1996;Lo and Dranginis 1998;Guo et al 2000).…”