Figure 4.

Cold stress sensing and signaling. Cold stress is sensed by membrane proteins such as COLD1, leading to a cytosolic Ca²⁺ signal. CPKs and CBLs-CIPKs may mediate the Ca²⁺ signal to activate a MAP kinase cascade. The activated MPKs are postulated to phosphorylate TFs such as CAMTAs and ICE1/2, which then activate cold responsive genes. Through an unknown mechanism, cold stress also activates OST1 (SnRK2.6), which inhibits HOS1, and phosphorylates and activates ICE1. Arrows indicate activation, bars indicate inhibition, and dashed lines indicate postulated regulation.