Nutrient-regulated adhesion in yeast and its regulation by a MAPK pathway
Karunanithi, Sheela Rani
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Nutrient limitation induces filamentous growth and biofilm formation in S.cerevisiae, among other responses. Both filamentous growth and biofilm formation require Flo11, a cell adhesion molecule regulated by the filamentous growth MAPK pathway along with other pathways. In this study, we show that Flo11 is shed from the cell surface. Flo11 is processed by a furin protease, Kex2 into a mature and functional protein. Shed Flo11 attenuates adhesion and promotes lubrication for mat expansion. Shedding calibrates cell-associated to shed Flo11 thereby optimizing invasion and mat expansion. Further, filamentous growth and mat formation occur together in response to nutrient limitation and is regulated by the MAPK pathway. The MAPK pathway regulates mat expansion (in the plane of the XY-axis) and substrate invasion (downward in the plane of the Z-axis), which optimizes the mat's response to extracellular nutrient levels. Finally, a new connection that directly links nutrient sensing to the regulation of MAPK pathway was identified. The cell surface protein, Opy2, regulates the filamentous growth pathway by recruiting Ste50 to the plasma membrane. Opy2 also associated with glucose-controlled transcriptional repressors, Mig1 and Mig2 which are required for filamentous growth pathway activity. Opy2, through Mig1 and Mig2 lead to a filamentous growth pathway-specific response. Therefore, by regulating Flo11 and also by communicating with the MAPK pathway, nutrient sensing pathways impact the adhesion behaviors in yeast.