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.
Highlights
Microbial species are single-celled organisms that typically grow and divide independently of other cells
The filamentous growth pathway regulates the expression of many genes, including the major yeast cell adhesion molecule, Flo11, which is required for both filamentous growth [42,43,44] and mat expansion [23]
We show that filamentous growth and mat formation are part of an integrated behavior that is regulated by the mitogen activated protein kinase (MAPK) pathway
Summary
Microbial species are single-celled organisms that typically grow and divide independently of other cells. In response to nutrient limitation, S. cerevisiae can undergo filamentous growth, in which cells form pseudohyphae that invade into substrates [22]. The filamentous growth pathway regulates the expression of many genes, including the major yeast cell adhesion molecule, Flo11, which is required for both filamentous growth [42,43,44] and mat expansion [23].
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