A MAPK cascade containing at least the Kss1 MAP kinase. It starts with the activation of Ste20, a MAP4K, which activates Ste11, a MAP3K, which in turn activate Ste7, a MAP2K, which activates Kss1. The kinases in each tier phosphorylate and activate the kinases in the downstream tier. The filamentous growth MAPK cascade is activated as a result of partial nutrient deprivation and  results in filamentous growth.
filamentous growth MAPK cascade