Gene regulation during cold acclimation in plants

Cold acclimation involves precise signaling and regulation of the transcriptome. The plasma membrane may be the primary cold-stress sensor, and FRY1/HOS2 inositol polyphosphate 1-phosphatase regulates cytosolic inositol-1,4,5-triphosphate levels, which in turn control cytosolic Ca2+ signatures and cold acclimation. Cold-induced reactive oxygen species may activate a mitogen-activated protein kinase cascade (AtMEKK1-AtMKK2-AtMPK4/6) that regulates tolerance to freezing and other abiotic stresses. Cold acclimation induces the expression of the C-repeat binding transcription factors (CBF), which in turn activate many downstream genes that confer chilling and freezing tolerance to plants. The constitutively expressed myelocytomatosis-type basic helix-loop-helix transcription factor inducer of CBF expression 1 (ICE1) regulates the transcription of CBFs and other cold-induced regulons and freezing tolerance. ICE1 is probably negatively regulated by ubiquitination, which may be mediated by the HOS1 RING finger protein. The ICE1-CBF pathway positively regulates the expression of cysteine-2 and histidine-2 zinc finger transcriptional repressors, which are under the negative control of LOS2, a bi-functional enolase. In a CBF-independent pathway, the transcription factors HOS9 (a homeodomain type) and HOS10 (a R2R3 myeloblastosis type) play pivotal roles in the regulation of cold-responsive genes and freezing tolerance. The signaling process from sensors to transcription factors and to cellular responses needs further understanding. Also, cold-stress signaling in reproductive tissues is still largely unknown.