Fig 7.

Model of Ste20 and Vma13 functions during filamentous growth. Low nutrient levels in cells growing on a solid surface trigger the PKA and filamentous-growth MAPK pathways. This results in cell elongation, increased adhesion, and growth into the substratum. We propose that, in addition to these signaling events, Ste20 activates V-ATPase, possibly via Vma13. This leads to a lower vacuolar pH, allowing optimal storage and mobilization of nutrients that are required for cell growth. Therefore, filamentous growth and allocation of nutrients complement each other.