FIGURE 2.

Proposed pathway of stalk cell induction by DIF-1. DIF-1 triggers an increase in cytosolic Ca²⁺, a process dependent on IplA, a protein related to the mammalian IP₃ receptor, which triggers Ca²⁺ release from the endoplasmic reticulum (Traynor and Kay, 2017) and may also induce Ca²⁺ entry into the cell via a store-operated calcium channel. The concentration of Ca²⁺/calmodulin in turn increases, binding to and activating the calmodulin-dependent protein kinase CaMKK2. This then phosphorylates and activates AMPK, which phosphorylates various target proteins, activating some (including calcineurin and inhibiting others (Sugden et al., 2015) and initiating the prestalk/stalk (ST) pathway.